|Late Blight Advice - September 22|
Fall is here and the days are short and the nights are long and the dew is on the crops for many more hours than it was back in July. All of that means that late blight spores can travel further with less risk of sun or heat killing them, and germinate if they get lucky and land on a tomato or potato plant. We were lucky this summer with weather that was very unfavorable to late blight and there was very little of it around the state.
Really only a small pocket of the state was hit hard and I feel sorry for those folks, many of them are reading this email.
For the rest of us it has been a fabulous tomato harvest, but now I am getting more calls and hearing more reports about late blight finds. I think it is so late in the season that we just accept it. We frosted the night before last here on my farm. A light frost that did not kill anything, but it is a sign that the plants are going to die and probably soon.
Remember, the fungus that causes late blight is an obligate parasite that only can live on living tissue. So, when the frost kills our plants, the late blight fungus will die too. That is going to happen soon so I would not worry too much if you find late blight. The tomatoes are still fine to eat, and those that are not infected will probably ripen up just fine.
Killing and bagging or burying the plants will prevent spread and that is why that was recommended through the season.
The concern now is about next year. Since late blight only survives on living tissue, the only place it survives winter here in New England is in potato tubers. Protecting tubers from infection, managing cull potatoes so any that are infected do not sprout next year and release spores, and scouting next spring for volunteer potato plants that may sprout from culls or potatoes missed during harvest are the three key activities.
Potatoes are at risk of getting infected. Of course, the leaves are infected first. Then, especially with a heavy rain, the spores may be washed down and infect the tubers. Or, tubers may be infected when harvested through diseased foliage. It may be worth your while to top kill potatoes and wait a week so there are not living spores at the time you harvest. This practice is also better for the potatoes too because the tubers cure after the tops are dead. Some folks wait until there is a good frost to kill the tops before harvesting. Actually, most potatoes are dead already thanks to the potato leafhopper.
Cull potatoes are the single most likely source of late blight infection each year. If they were just laying on the ground that would be best because they would freeze, die and thus the late blight dies with them. But many people make piles of culls, throw them in compost piles that get warm but not hot, let them get buried in the field, i.e., all sorts of things that keeps them from freezing. Then next spring they sprout and a sprout from an infected potato will be infected and release spores to start the disease spread again.
Please do not let any late blight infected potatoes sprout next year. Scouting for volunteer potato sprouts next year is the last and important practice you have available to protect you and your neighbors from late blight. If you see any volunteer sprouting potatoes next spring, kill them.
Pest Report - August 23, 2010
In this issue:
- Corn Smut
- Some common summer disorders of vegetables
- When is my winter squash ready to harvest?
Late Blight Update
There is quite a bit in Knox and Lincoln county but very little elsewhere in the state. If you think you may have late blight in your crops, please contact Eric Sideman, MOFGA's Organic Crops Specialist, at firstname.lastname@example.org
Corn smut often occurs in fields but usually losses are very small. Rarely does one find more than an infected ear here or there. Once you see it you will never forget it. Roundish galls that are from a half inch to an inch and a half in diameter and range from glistening white to green form in the ears. As they grow they burst the ear open and the ear is filled with these galls. The disease is favored by dry conditions and poor fertility. I have seen more than usual this year. The organism that causes smut is in the group of fungi that include mushrooms. It is not surprising that some people consider the smut gall delicious gently fried in butter. Similar to the other fungi in this group, there are a few different kinds of spores produced. The spores released from the galls (teliospores) overwinter on the soil and germinate in the spring to release another kind of spore (basidiospores). These spring-produced spores blow in the wind and if they land on corn they germinate and can infect the ear through the silk. Proper fertility and irrigation help. If you find an ear full of galls, pick the ear and burn it before the galls rupture and release spores.
SOME SUMMER DISORDERS
(Reprinted and modified a bit from an article by Becky Sideman in the August University of New Hampshire Vegetable, Berry and Tree Fruit Newsletter)
While pests and diseases are troublesome, it is often disorders caused by abiotic stresses that cause the most aggravation for growers. With the high heat we have experienced this summer, growers have reported seeing some of the following disorders. Understanding the causes of some of these issues may help you prevent them in the future, or at the very least, might help reduce your frustrations!
Tomato Physiological Leaf Roll
Physiological leaf roll starts with upward cupping of leaf margins and eventual inward rolling of the leaves. This phenomenon has been associated with heat and prolonged periods of wet soil; conditions that are common in well irrigated high tunnels. High-yielding indeterminate varieties seem to be more prone to leaf roll, and the problem is more pronounced on heavily pruned plants. While plant growth, fruit yield, and fruit quality are not believed to be affected by physiological leaf roll, in extreme cases, sunscald could be more likely when leaves are strongly curled.
|Pruned tomato plants in a high tunnel showing physiological leaf curl.
Management tactics: plant determinate cultivars, maintain adequate but not excessive soil moisture, do not overfertilize, provide adequate levels of phosphorus, avoid severe pruning, and maintain cool temperatures through the use of ventilation, shading.
Tomato Internal White Tissue
In fruits with this disorder, portions of fruits remain hard and white while the rest of the fruit ripens normally. The hard white tissue may be spread throughout the pericarp or, more commonly, may be concentrated in the outer wall of ripe fruit. The white tissue can range from a few white fibers to a solid white mass. Fruits within a cluster may not be evenly affected. This disorder has been shown to be caused by poor potassium nutrition and heat stress; though other factors may also be involved.
Management tactics: Provide adequate levels of potassium, maintain cool temperatures through the use of ventilation or shading.
Waxy Breakdown of Garlic
This disorder is a physiological degradation of the garlic cloves after harvest. It begins as small, sunken, light yellow areas appear on the clove tissue. These areas enlarge and the affected cloves eventually turn deep yellow amber. The tissue becomes translucent and sticky or waxy. The problem may be obscured by the coverings of the cloves, until the cloves shrink and the dark amber color is visible through the outer coverings. This disorder is poorly understood. High temperatures during growth and/or after harvest, and poor ventilation and/or low oxygen during storage, have been proposed as causes of this disorder, but these have not been confirmed.
Sunscald or White Drupelet Disorder of Raspberry
The raspberry fruit is an aggregate fruit that contains many individual fruits called ‘drupelets’. As the raspberry ripens fruits with white drupelet disorder have some drupelets that turn white and never ripen completely. Stinkbug damage is similar in that it causes a random pattern of white spots on mature fruit, however, in the case of white drupelet disorder and/or sunscald, the cooler side of the fruit will appear normal. Varieties vary in their susceptibility to sunscald.
Management tactics: Avoid planting in sites with strong summer winds, which can promote sunscald. Orient planting rows north-south. Shading after pollination, using a shift-trellis system, and installing overhead irrigation for mid-day (not late afternoon) evaporative cooling) can all help to minimize sunscald.
Acknowledgements: Damicone and Brandenberger, Oklahoma State Univ. Bull. EPP7627: Common diseases of tomato part III: Noninfectious diseases; Pacific Northwest Vegetable Extension Team Bulletin PNW616: Physiological leaf roll of tomato; New York Berry News Vol.4 No.8 August 18, 2005; and Cantwell, Garlic Recommendations for Maintaining Postharvest Quality, UC Davis Postharvest Technology Research & Information Center.
PUMKIN AND WINTER SQUASH HARVEST AND STORAGE
(Reprinted and modified a bit from an article in the U Mass Vegetable Notes by Ruth Hazzard)
Winter squash and pumpkin fruit sitting in the field face a daunting list of diseases and insects – not to mention possible passing hurricanes -- that could threaten fruit quality. Early harvest and careful storage is often preferable to leaving fruit in the field. This is especially true if you know that your pumpkins or squash are in fields that are infected with Phytophthora blight.
Since the pumpkin market lasts from Labor Day to Halloween, pumpkins may need to be held for several weeks before they can be marketed. When is it best to bring then in, and when to leave them in the field? If the vines are in good condition, the foliage can protect the fruit from sunscald. If foliage is going down from powdery mildew or downy mildew, this may help with ripening and make harvesting easier, but also increases the risk of sunscald or injury to pumpkin handles. There can be extra work involved in bringing fruit in early, especially for growers who normally have pick-your-own harvest, but we recommend that growers harvest as soon as crops are mature and store under proper conditions, if it is feasible. Attention to curing and handling will go a long way toward improving the life of winter squash and pumpkin fruit.
What about pumpkin stems, i.e., handles? In some cases, it’s the handle that sells the pumpkin. Pumpkins may not be marketable if the handle is broken off or dried up. Ideally, if the timing is right, pumpkins would be cut one to two weeks prior to marketing. However, if they are harvested now they may sit much longer before being sold. The discussion of how early to cut handles is an old one with many different opinions. One view is that it is advisable to cut the handles from the vine to save them from advancing powdery mildew and reduce shrinkage. Whether or not handles shrink and shrivel after cutting is affected by plant stress, genetics (variety), moisture and temperature conditions, and disease. There are many diseases that can affect handles, including Plectosporium, Fusarium, Black Rot, and Alternaria. Again, proper curing and storage conditions are key.
Ideally, pumpkins should be harvested when fully mature, with a deep orange color and hardened rind. However, as long as pumpkins have started to turn color, they will ripen off the vine if held under the proper conditions. While not ideal, this may be preferable to leaving them in the field if conditions are not favorable. If necessary, pumpkins can be ripened in a well-ventilated barn or greenhouse. The best temperatures for ripening are 80-85 degrees Fahrenheit with a relative humidity of 80-85%. Night temperatures should not drop below the sixties. Even if pumpkins are ripe, a period of curing can improve storage life. The curing period should be about 10 days. During this process, the fruit skin hardens, wounds heal and immature fruit ripens – all of which prolongs the storage life.
Pumpkins should be stored in a cool, dry place. Ideal temperatures are between 50¡ and 60¡ F and relative humidity of 50 - 70%. Higher humidity allows condensation on the fruit with risk of disease, and lower humidity can cause dehydration. Higher temperatures increase respiration and can cause weight loss. Temperatures lower than 50 F cause chilling injury (see squash, below). In a greenhouse, temperature can be managed with ventilation on sunny days. Unless it is quite cool, heat is not likely to be needed if the house is closed up at night.
Often it is not feasible to harvest pumpkins early and store them until they can be marketed, and so they must be ‘stored’ in the field. If vines and fruit are healthy, storage in the field can be successful for a few weeks. If the vines die back, damage to the fruit from sun, disease and insects is more likely. In any case, it is important to scout for insects feeding on the fruit and handles, which may include squash bug nymphs or adults, or striped cucumber beetle. Control them if damage is evident. In fields that have a history of Phytophthora blight, Fusarium fruit rot, or black rot, field storage may increase the incidence of these problems, particularly if we have a period of wet weather or a major storm while fruit is sitting in the field. This has been one of the causes of significant losses in recent years, and one reason that we recommend bringing fruit in as soon as it is mature.
Growers often plan to store winter squash for much longer than eight weeks. Fruit that are free from disease and haven’t been subject to much chilling (below 50¡F ) should be selected for long-term storage. Many years the challenge is to harvest the winter squash before it is subject to much chilling, but waiting long enough for it to be ripe. This year much of the winter squash began to look ripe in early August, but it was not. Even though it had the right color and a tough rind, it did not have the sugars yet for good taste. It is quite a challenge to tell when winter squash is ripe. To learn more about this see Blanchard, Chris. 2000. Harvest timing critical for winter squash. Growing for Market. September. p. 1, 4–5.
Storage life depends on the condition of the crop when it comes in and your ability to provide careful handling and a proper storage environment. All fruit placed in storage should be free of disease, decay, insects, and unhealed wounds. When harvesting squash and pumpkins, it is important to handle the fruit with care to avoid bruising or cutting the skin. Despite its tough appearance, squash and pumpkin fruit are easily damaged. The rind is the fruit’s only source of protection. Once that rind is bruised or punctured, decay organisms will invade and quickly break it down. Place fruit gently in containers and move bins on pallets. Use gloves to protect both the fruit and the workers. Removal of the stem from squash (butternut, Hubbard, etc.) will also decrease the amount of fruit spoilage because the stems frequently puncture adjacent fruit, facilitating infection.
A period of curing after harvest can help extend storage life of squash. This may be done in windrows in the field -- especially with a series of warm, dry days -- or by placing squash in a warm dry atmosphere (70-80¡F) with good air circulation, such as a greenhouse, for up to two weeks. This pre-storage treatment permits rapid drying of the outer cell layers, and when combined with a dry atmosphere for storage inhibits infections that can take place at this time. Any clean cuts during harvest a likely to heal over and are no longer a source for injury or infection.
Take care to avoid subjecting squash to chilling injury. Chilling hours accumulate when squash or pumpkin is exposed to temperatures below 50¡F in the field or in storage. Injury increases as temperature decreases and/or length of chilling time increases. Chilling injury is of particular concern with squash intended for storage because it increases the likelihood of breakdown. If squash has been exposed to chilling injury it should be marketed first and not selected for long-term storage. Remove squash from the field if temperatures likely to drop below fifty degrees for any length of time.
After curing, move squash or pumpkins to a dry, well-ventilated storage area. Pressure bruises can also reduce storage life, so avoid rough handling, tight packing, or piling fruit too high. Fruit temperature should be kept as close to the temperature of the air as possible to avoid condensation, which can lead to rot. Ideally, the storage environment should be kept at 55-60¡F with a relative humidity of 50-70%. Lower relative humidity increases water loss, resulting in reduced weight, and if excessive, shriveling of fruit. High relative humidity provides a favorable environment for fungal and bacterial decay organisms. Under ideal conditions, disease-free pumpkins should have a storage life of 8-12 weeks and butternut squash up to three or four months. Even if it is difficult to provide the ideal conditions, storage in a shady, dry location, with fruit off the ground or the floor, is preferable to leaving fruit out in the field.
As you plan for storage and marketing, keep in mind that the market for pumpkins seems to get earlier every year. Fall decorative displays include pumpkins, and those displays begin showing up as Labor Day approaches. One of the best solutions to early-maturing pumpkins may be finding an early market.
--R. Hazzard; many thanks to the following sources: J. Howell, A. Carter, and Robert Wick. University of Massachusetts; Dale Riggs & Robert Rouse, Pumpkin Production Guide, NRAES; Maurice Ogutu, University of Illinois Extension, in Vegetable Growers News, August 2004; and Liz Maynard, Purdue University; Andy Wyendandt, Rutgers Univ.
Pest Report - August 9, 2010
LATE BLIGHT UPDATE
Late blight is still being reported only in a handful of sites in Maine, in gardens and a few market farms. At this point I have confirmed reports from the Waldoboro area, Appleton, Stockton Springs, and a new site in Dixmont. I am fielding many, many pictures of things that are not late blight. The most common of these are leafhopper damage, early blight, Septoria leaf spot and Botrytis. I am getting the question often whether or not to spray, and to be safe I would be spraying, but at this point I still think the spread is going to be minimal so many folks may want to take the risk of not spraying. I hope I am not wrong.
POTATO LEAFHOPPER UPDATE
|Potato Leaf Hopper Damage. Photo by Eric Sideman.
The potato leaf hopper is wide spread in central and southern Maine. I am seeing lots of potatoes that have gone down and look like they died from a disease. I am also seeing the symptoms on beans (pale, yellowing leaves) and cucurbits (narrow yellow to browning edge on leaves). As I mentioned in earlier Pest Reports (ex. June 24), spraying for this pest must happen based on scouting and finding the insect. By the time you see symptoms on the plant, it is too late.
IMPORTED CABBAGE WORM
The white butterflies are flying all around the cabbage family plants now and laying eggs, and the larvae (green caterpillars) are chewing holes in the leaves. If you have heading broccoli you must know your customers because some folks are really turned off by the critters floating to the top of the water in the cooking pot. You may want to spray even though the crop is beyond risk.
This pest overwinters as a pupa and there are 3-4 generations per year. This means that once you start seeing the butterfly you should start scouting for the caterpillar in about a week. Bt (Dipel 2X or Dipel DF) or Entrust work very well in controlling the caterpillar. None of these materials lasts in the field and so should only be sprayed when the caterpillars are there in large enough numbers to warrant it.
|Imported cabbage worm. Photo by Eric Sideman.
Destroy or bury crop residue after harvest so as not to allow the caterpillars to continue to feed and complete their life history and thus a larger second generation.
NOTE: Diamondback moth is also very common (see Pest Report July 7).
SCARAB BEETLE UPDATE: JAPANESE, ORI¬ENTAL AND ASIATIC GARDEN BEETLES ARE ACTIVE
(Modified from a Report in the U Mass Vegetable Newsletter)
Japanese Beetles widespread and showing up in various crops and non-crop habitats, even though the numbers are down from years past. Oriental Beetles are also active and, though less damaging, may appear in vegetable fields as well. Asiatic Garden Beetles is evident mostly through their damage, because they feed at night. There are four species of scarab beetles that are common in New England turf, fruit and vegetable crops. These were all introduced to the US. Japanese beetles are the most common and widely distributed, but Oriental and Asiatic Garden beetles are expanding their range and activity. Below are brief descriptions.
LIFE CYCLE . The life cycle of the Japanese beetle fits most of the spe¬cies of grubs we encounter in New England, with minor varia¬tions depending on the species and the location. They have a one-year life cycle, with adults emerging from the soil in July to feed and mate. The females burrow into the soil (often in or near wide expanses of grass or sod) to lay eggs, usually beginning in late July and August. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads). The first grubs usually appear around mid-August and begin feeding on roots of grasses and other plants (especially corn). After about two weeks of feeding, the grubs molt to a second “instar”, and feed for another three weeks. The grubs molt once more, to the “third instar” (or large grub) around the middle of September, and continue feeding until the soils begin to cool down. In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding for about six weeks. By the middle of June, most grubs have completed their feeding requirements and pupate (still in the soil) for about a week before emerging as new young adults.
- JAPANESE BEETLE adults are about half an inch long, with a metallic green head. The wings are shiny copper or bronze color, and there are a few tufts of white “fur” along the side of each wing when it is folded back over the body. The adults are active in daylight and feed on many different kinds of trees, fruit and flower crops. Fruit and ornamental plants are preferred, but beetles can congregate in vegetables also. In vegetables, adults can cause silk clipping in corn, and leaf damage in sweet basil, collards, other greens, green beans, eggplant, asparagus, rhubarb, and peppers. Though numbers may be high, there is no need to treat unless actual feeding damage is significant. In corn, if there are more than two Japanese beetles per ear and corn is less than 50% pollinated, an application may be warranted to reduce clip¬ping and ensure adequate pollination.
|Asiatic garden beetle. Photo by Eric Sideman.
- ASIATIC GARDEN BEETLES are about half as long as a Japanese beetle adult, and somewhat more “plump” or domed in appearance. They are reddish-brown or dark copper-colored. They often are found near roots of plants when one is weeding. Adults tend to cause more damage to vegetable crops than Oriental Beetle, but less than Japanese beetles. Because they feed at night, one may find damage without seeing the beetles. During the day they hide in the loose soil or mulch around the base of the plants. Scout with a flashlight at night, or sift through soil to find them. Larvae feed on beet, carrot, corn, lettuce, onion, Swiss chard and strawberry. Adults feed on carrot, beet, parsnip, pepper and turnip. One grower reported heavy beetle feeding on peppers that were held under row cover through the end of June: this could be the result of Asiatic garden beetles that emerged under the cover. He could not find beetles, only damage. Beware the events that occur under row cover while unsuspecting farmers are looking the other way!
- ORIENTAL BEETLES fly at night, but are very active during the day as well. The beetles are smaller than Japanese beetles, and usually are a rather mottled gray with black splotches. The pattern and color varies. Occasionally an individual will be al¬most all black or almost all gray. The antennae are branched and are quite striking if you take a close look. Oriental beetles have a long flight period – through early August – and are very mobile. Adults tend not to feed heavily in vegetable crop foliage. Grub damage may be worse in drought years and in weedy fields, but is not commonly a problem in vegetable fields and crops, though this is not well studied.
- A fourth species may also be found: EUROPEAN CHAFERS, which are slightly larger than Japanese beetles and are a fairly dull brown or tan in color. They are night fliers but can be seen in large numbers just at sunset, when they congregate in large numbers in favorite trees (such as locust or willow). Adults are not foliage feeders and grubs are mostly a turf problem.
CONTROLS. There are not many controls for organic growers to choose from. Beneficial nematodes work fairly well on the grubs if there before the population explodes, but for vegetable grower the adults are the critters that cause most damage and they are good fliers so your control of grubs in your sod fields will not likely reduce the damage. Neem and pyrethrum offer fair control of the adults.
R. Hazzard, adapted from Pat Vittum, Turf Entomologist, UMass, Beth Bishop, Michigan State University, Michael Seagraves, Cornell Cooperative Extension, and Ann Hazelrig, University of Vermont
SPIDER MITES ON CUCUMBERS
Usually, natural enemies keep spider mites in check, but this year either the very dry weather or broad spectrum insecticides sprayed for leafhoppers or something else have lead to two spotted spider mite populations causing lots of damage. Spider mites puncture the cells of the leaves and extract juice. This results in the cell dying and the leaf getting a stippled appearance where the mites are feeding. As the feeding progresses the leaves become pale, mottled and then leather and then shriveled and desiccated. If you use a good magnifying glass (better yet, a hand lens) you can see the webbing caused by the mite, and the mites running around. They are very, very tiny. They are not insects (class Insecta) but are in the same class of Arthropods as spiders (class Arachnida) and have so 8 legs.
|Spider mite damange on cucumber plants. Photo by Eric Sideman.
Scouting for mites should begin early in the season. They are more commonly a problem in greenhouse cucumber production than field production. In greenhouse production the release of predators is the best means of control. In field production one hopes for, and usually gets plenty of natural predators. Avoid spraying broad spectrum insecticides such as pyrethrum. If they build and it is early enough in the season to warrant control, neem oil and insecticidal soaps may help if the mites are spotted early.
Hornworms are probably the most destructive insect attacking tomatoes and they are showing up now in hoophouse tomatoes. They are giant caterpillars that can do a vast amount of eating in a very short time. Sometimes it seems that overnight healthy looking tomato plants are striped of their leaves leaving bare stems. The hornworms will also attack the fruit eating gouges out so large that they look more like bites of a furry animal than an insect. Look now for the damage and the frass, which is black pellets lying all around plants hosting hornworms. The frass may be your first sign there is a problem.
The adults are large, fast flying hawk moths, which in flight may look like a hummingbird. At dusk they hover over flowers sucking nectar. Eggs are laid on tomato leaves and hatch in 5 days.
Hand picking is a bit frightening but does work and chickens enjoy fighting with the challenging pest. The problem with hand picking is that they blend in very well and it is easy to overlook one or two caterpillars that can do significant damage in a day or two.
Bt works very well on this caterpillar, especially when they are small.
WHAT ARE THOSE WHITE THINGS ON TOMATO HORNWORMS?
Tomato hornworm larvae are parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as many small white projections protruding from the hornworm‚s body. Parasitized hornworms should be left in the field to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize. (Reprinted from 2005 Vermont Veg and Berry News by Vern Grubinger)
|Braconid wasp parasites on tomato hornworm. Photo by Eric Sideman.
Pest Report - July 26, 2010
LATE BLIGHT (Phytophthora infestans)
At this time late blight is only in one location in Maine. The center of it seems to be the western part of the Waldoboro area. Similar to the other occurrences this year in PA, CT and NY, it seems to be an isolated breakout. The good weather of this week should support that. But continue to be vigilant and out there scouting. If you are within 50 miles of there, you should consider spraying one of the approved copper fungicides. Check your email at least once a day for updates and don't hesitate to ask questions.
|Powdery mildew damage on a cucumber plant (above). The first symptoms of powdery mildew on underside leaf surfaces are white, powdery fungal patches (below). Photos by Eric Sideman.
POWDERY MILDEW (Podosphaera xanthii)
Powdery mildew is a common disease of pumpkins and winter squash. All cucurbits are susceptible, but many common cucumber and melon varieties are resistant. The disease can cause infected leaves to die prematurely, reducing yields and lowering fruit quality, especially taste. Winter squash from diseased plants won’t store as long as fruits from healthy plants. The fungus that causes the disease does not overwinter in Maine. Spores blow up every year from southern overwintering sites. If they arrive late in the season, you may not need any control; but if they arrive in early to midsummer, exercise some control or you may have no leaves by mid-August.
Powdery mildew reports are now coming in to me. This may warrant attention. Go out and scout.
Check upper and lower surfaces of leaves of older plants every few days starting now. The first symptoms usually are white, powdery fungal patches on the undersides of older leaves. Yellow spots may form opposite these, on the upper leaf surfaces.
No products with systemic activity (products that move through the plant) are approved for organic production, and applying fungicide to the lower leaf surface is difficult. In experiments, foliar applications of sulfur have been more effective than most other organic products for powdery mildew, apparently because sulfur deposited on the upper leaf surface can volatilize and be redistributed to the lower surface. Sulfur can be phytotoxic on melons, especially if applied when temperatures are hot.
ATTRA (National Sustainable Agriculture Information Service, www.attra.ncat.org) reports that a single spray application (to runoff) of 0.5 percent (wt./vol. of water) baking soda, plus 0.5 percent (vol./vol. of water) SunSpray UFP® horticultural oil almost completely inhibited powdery mildew on heavily infected pumpkin foliage; while baking soda without the oil was ineffective, and a 2 percent (wt./vol. of water) solution of baking soda damaged the leaves. But, remember if you are a commercial grower then you must be using EPA registered pesticides and not homemade concoctions.
LEAFHOPPERS (Empoasca Fabae)
The report I presented on leafhoppers a few weeks ago (Pest Report June 24, 2010) warned that they were taking down potatoes, and they did. In my travels last week I saw potatoes on their way down. If leafhoppers where into your beans or potatoes back then, I suspect you see the crop dying now with the edges of the leaves turning brown then crisp and the plant getting weaker and weaker. I have received numerous calls confusing this (or damage from the tarnished plant bug, Pest Report from July 7, 2010) with late blight. Once you see the damage, it is too late to spray.
|Symptoms of black rot of brassicas are irregular, dull, yellow areas along the margins of the leave that expand in a "V" shape. Photo by Eric Sideman.
BLACK ROT OF BRASSICAS (Xanthomonas campestris)
Black rot is one of the most important diseases of brassicas world wide and is much more of a problem in warm, humid climates than in the cool northeast. Still, it is very common here and does result in crop loss. The disease is caused by a bacterium called Xanthomonas campestris. The initial infection is most often through seeds and infected crop debris. The bacteria are spread by rain splash, insects, workers, and equipment. The symptoms are irregular, dull yellow areas along the margins of the leaves that expand in a "V" shape (see picture on MOFGA website). The veins in the lesions often look dark. Sanitation is the key to avoiding this disease, but the problem is that sanitation is most important during seed production. Buy seeds from a reputable source. Begin sanitation when raising seedlings. Any yellowing seedlings or plants with "V" shaped lesions should not be planted in the field as they will serve as a source of bacteria that may spread to the whole field. There are resistant varieties. Crop rotation (3 years) is important so if you have this problem pay attention to which fields and clean equipment so you do not drag crop debris to new fields. Avoid overhead irrigation, but of course this year that would make no difference. Do not use manure from livestock that have been fed diseased Brassicas on fields intended from Brassica crops. Hot water treated seed is recommended. For cabbage and Brussels sprouts soak seed for 25 minutes in 122 F water, and for broccoli and cauliflower soak for 20 minutes. Precise time and temperature control is essential to minimize damage to the seed.
|Purple blotch lesions begin as whitish sunken areas that elongate and develop purplish centers. Photo by Eric Sideman.
PURPLE BLOTCH (Alternaria porri)
Purple is a very common and sometime destructive disease that effects onions, garlic, shallots and leeks. Lesions begin as whitish sunken areas that elongate and develop purplish centers. Under favorable conditions (warm with wet leaves) the purple blotch lesions grow large and oval with concentric rings. The lesions may merge and take down whole leaves, and may become covered with brownish spores. The older leaves are more susceptible than the younger leaves.
Onion residue is the source of the disease in the spring. The fungal mycelium and conidia spores persist as long as the onion debris in the field or in cull piles. New conidia are produce on infected tissue in the spring and wind blown or carried in water to the new crop. The leaves have to have liquid water on them for the spores to germinate, but germination is very quick, less than an hour. Symptoms may appear in less than a week after germination and new conidia spores are quickly produced.
Sanitation is very important to limiting spread. Infected crop debris should be destroyed or buried after harvest. Cull piles should not be kept near the new onion field. Onions should be grown in rotation with non host crops.
Materials Approved for Organic Production
Serenade has been shown to be effective against purple blotch.
The latest update on late blight is not good news. It has been found by scouts on a few more farms in the Waldoboro region. These have not been confirmed yet in the lab, but the field observations were on tomatoes and potatoes on commercial farms.
This means that growers in that area should be very vigilant scouting, and seriously consider applying copper as a protectant even if no signs are found.
Organic growers must use a formulation of copper that is approved for organic production. Champ WG, NuCop 50 WP, and Cueva Fungicide Concentrate are approved for organic production. BUT, NuCop 50 does not seem to be registered in Maine. If your supplier has only that, then you should ask them to call the Board of Pesticide Control Office (287-2731) and talk to them about getting it registered. It must be registered for use as a pesticide. Also, farmers are not permitted to use formulations of pesticides that are only registered with the EPA for gardener use. Any pesticide registered for farm use will have Worker Protection Standards on the label.
Eric Sideman, MOFGA's Organic Crop Specialist will provide more information as it develops. Stay tuned and direct any questions to Eric at email@example.com.
The first confirmed report of late blight in Maine just came today.
A gardener in Waldoboro, Maine has late blight on tomatoes.
At this time we have no more details but will surely post them all as they develop.
Please go out now and scout your potatoes and tomatoes for signs. Get back to Eric Sideman <firstname.lastname@example.org> if you suspect it. There are a lot of problems out there that can be confusing. For example, as noted in Eric's Pest Reports, blackleg, early blight and tarnished plant bug feeding all can be mistaken for late blight.
If you don’t know what to look for, take a look at these fact sheets.
Pest Report - July 7, 2010
WHITE ROT OF GARLIC (Sclerotium cepivorum): It is only a month or so before it is time to harvest the garlic and growers should be aware of any diseases they have because a sure way to infect next year's crop is to use diseased seed. Of all the problems white rot is the most horrible. It is a horrible problem because it may spread fast, and once in a field it can take many, many years to get rid of. Inspect your crop now, and inspect your crop when you harvest it. Do not use or sell or buy any infected seed. If you have white rot, then you should not grow garlic in that field for many, many years.
White rot is one of the most destructive fungal diseases that affect the onion family. It is only a problem in the onion family. [It is not the same pathogen as white mold, which attacks many other crops such as beans, carrots, lettuce, tomato, pepper and more]. Symptoms of white rot on the leaves include premature yellowing and dying of the older leaves and then death of the plant. That is not much different than many other garlic problems, but the white, fluffy fungal growth (mycelia) on the root end of the bulb is the give away. Eventually this fungal growth moves around the bulb and inward between the storage leaves of onion and cloves of garlic. Small, black sclerotia (tiny hard, black bodies of dormant mycelia) form in the decaying tissue and throughout the white fluffy mycelia. Secondary infections by other fungi may occur.
There are no known spores. This fungus reproduces only by the sclerotia, and it spreads by direct contact. The sclerotia can lie dormant in the soil for many years until roots of a host plant grows nearby and the sclerotia are stimulated to germinate. Germination is optimum between 57 and 64 degrees and fungus growth optimum in soil is in the mid 70s with good soil moisture, but growth slows with warmer temperatures. The fungal growth spreads away from the infected plant and if it makes contact with a new plant it infects that one. So, the disease quickly spreads down rows of onions and garlic. Restricted areas of a field may be effected and other areas not. That is, until you drag the pathogen around on your boots or tiller or other equipment, or it flows with soil in heavy rains.
The pathogen spreads commonly by movement of infested soil on equipment and boots and by planting infected garlic seed, onion sets and transplants. Animals feeding on diseased bulbs can defecate viable sclerotia.
I have come across an interesting idea for speeding up the eradication of white rot sclerotia from the soil. Remember that the sclerotia will sit waiting in the soil for 20 or more years until a signal is received that onions or garlic are growing nearby. The growing allium releases a chemical that the sclerotia can sense. Over the past decade or so researchers have been playing with this knowledge trying to come up with a system that gets the sclerotia to germinate but, of course, have no alliums growing for the pathogen to complete its life cycle, thus reducing the number of sclerotia. I don't have a specific recommendation but a few things I have heard about that can reduce sclerotia in the soil include: 1) growing scallions which stimulate the sclerotia but are harvested before the disease spreads and new sclerotia are formed, 2) making compost out of onion waste and spreading that in the spring or fall repeated for a bunch of years before trying to grow an allium again, 3) making a concoction from ground up onion or garlic waste, or using garlic powder as a soil amendment for a few years before trying to go back to an allium. I wish I had a solid recommendation, but science is slow and this is a very complex problem. For now, pay attention to the stuff below.
Disinfectant Guidelines to Prevent the Spread of White Rot: The fungus that causes white rot is capable of surviving for many years as dry sclerotia on the surfaces of storage crates and bins and on harvesting and tillage equipment. In order that the fungus is not spread MOFGA recommends that all surfaces that may have been in contact with the disease, including boots, be sanitized with an appropriate disinfectant. Seed producers should execute extra diligence and may want to regularly disinfect any surface in contact with garlic.
Equipment, storage bins, etc should be effectively pressure-washed and then disinfested for ten minutes with sodium or calcium hypochlorite, (for example, 1:10 dilution of a household bleach such as Clorox, which is 5.25% NaOCl). Then rinse with potable water.
Since organic matter stuck on boots will inactivate chlorine materials, quaternary ammonium compounds may be used as boot dips inside storage areas and packing sheds, and before and after leaving fields. Quaternary should not be used on any apparatus that is in direct contact with the garlic or onions. Disposal of the dip solution must be in a manner that does not contaminate the soil, water or crop. Note: not all quaternary ammonium products are labeled for boot washes so read the label.
Best control is by good sanitation. Use clean seed for garlic and clean onion sets and transplants. If the infection is low, which is usually the case the first year it is found on a farm, pull the infected plants and destroy.
LATE BLIGHT UPDATE: At this time there is no late blight reported in northern New England. I am getting lots of emails and pictures of things that are not late blight and it is great to know that so many farmers and gardeners are being vigilant in their scouting.
The two most common culprits that are being thought of as a possible late blight symptom are blackleg (covered in the June 24, 2010 issue of the Pest Report), and feeding done by the tarnished plant bug (TPB).
TARNISHED PLANT BUG: The tarnished plant bugs, and other plant bugs, are rampant this year. I have never seen such numbers as in the clouds that rise out of my potatoes when disturbed.
|Tarnished plant bug - note damage in upper right corner of picture. Photo by Eric Sideman.
Generally TPB is not a serious pest of potatoes. Even with the clouds this year the damage is minimal. But some leaflets are wilting and turning brown (see the picture in the web version of this report), and being mistaken for late blight.
The tarnished plant bug is a small (6 mm), bronze, brown and black bug that feeds on a very wide variety of plants. They overwinter as adults under debris and become active early in the spring. There are three or more generations per season. They are serious pests on strawberries (causing cat faced berries), lettuce (browning of midrib), flowers (destroying buds), eggplant and pepper (destroying buds), broccoli (brown beads in the head), and much more. But in potato they basically kill flowers (who cares?) and damage some of the leaflets (minor problem). It is pretty easy to kill them with pyrethrum, but not worth it because their numbers are so great in all the fields of hay and weeds surrounding you that what you kill will be replaced in a day or two. Weed and neighboring field management is about all you can do to keep the numbers low.
CATERPILLARS IN BRASSICA CROPS: There are three common caterpillars that feed on our broccoli family crops. Keep an eye out for them.
Quick ID Cues:
Diamondback moth caterpillar: very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons, with a green full-grown caterpillar or a brown pupa inside. They eat wholes in the leaves.
|Diamondback moth caterpillar. Photo by Eric Sideman.
Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow. They eat large chunks out of leaves
Cabbage looper: light green, smooth, loops up like an inchworm as it moves, grows 1 1/2 to 2 inches. Eats big holes in leaves.
Scout undersides of leaves to look for fresh damage and notice and get control of caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.
For organic growers both Bt and Spinosad are very effective (Bt products are a lot cheaper), but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying.
Destroy crop after harvest so it does not act as a harbor for the pests all season.
MEASURING INSECTICIDES FOR BACKPACK SPRAYERS AND SMALL PLANTINGS: (Modified, short version of an article by Ruth Hazzard in the U Mass. Veg. Newsletter. For the complete article with examples go to http://www.umassvegetable.org/newsletters/current_news.html and look at the June 17, 2010 issue)
Growers with diverse crops and small plantings often need to be able to apply pesticide to beds or plots of several hundred square feet rather than acres, and the pesticide labels often only give rates on per acre basis. It is important to use the correct amount of insecticide in your backpack sprayer when spraying a small area. Calibration and mixing require some basic math, as do a lot of aspects of farming! The methods for backpack sprayers and tractor sprayers are essentially the same. Figure out the area to be sprayed and how much pesticide is needed for that area. Measure the amount of water you need to cover a known area, using the same equipment and walking or driving speed that you will use when spraying. Then ‘do the math’ so that the insecticide and the water rates both match your target area. Why does it matter? Why do you need to be careful about these rates? 1. Effective control of the pest depends on correct rates. 2. You are legally responsible for following the label instructions. This is especially important when you are selling the crop to the public. 3. The safety of the applicator, workers and the public depends upon correct rates and using pesticides according to instructions on the label.
Read the label. Find and follow the following instructions: --Personal protective equipment (PPE) – what you must wear when mixing and spraying. --Agricultural Use Requirements – this tells what protective equipment you should wear. --Crops and pests listed. The pesticide MUST be labeled for the target crop. --Restricted Entry Interval (REI) – during this time, no one should work in the sprayed area unless they are wearing protective equipment. --Days to Harvest (DH) – how long you must wait after a spray before harvesting (note: days to harvest may be less than REI; it is not a misprint) --Rate per acre or concentration per gallon (for backpack sprayer) --Mixing instructions.
The label often uses inconvenient measures. Conversions are key to your calculations. Here are some conversion ratios: 16 dry oz (by wt) = 1 lb One ounce (dry weight) equals 28.45 grams. 32 fl oz = 1 qt. 128 fl oz = 1 gal Liquid measure in (fluid) ounces is already a volume so it is easier to measure. One fluid ounce equals 6 teaspoons (tsp) or 29.6 milliliters (ml). An inexpensive measuring device for ml can be found in the children’s medicine section of drug stores. 43560 sq ft = 1 acre.
Entrust, for example- Based on repeated samples, we have found that there is 1.7 gm per teaspoon (shaved level and tamped slightly). So for Entrust the recommendation is 1.3 grams (3/4 teaspoon) in 3 gallons of water for 1,000 sq. ft.
ANTS: I used to consider ants my friend. They aerate the soil, play a big role in decomposition and recycle nutrients, and for the most part do little damage out in the fields.
|Ants girdling base of stem of Brussels sprouts seedling. Photo by Eric Sideman.
But this year they have girdled my Brussels sprouts and broccoli, wiping out entire rows. In the past I have seen them take down pepper plants and beans too, but usually only small numbers of them in a field. I have been told by Frank Drummond and Ellie Groden that they are looking for water or trying to get rid of plants I may have placed on top of their nests. I wish they would move elsewhere.
SQUASH BUGS: (Modified from article in U Mass Veg. Newsletter by Andy Cavanagh) Squash bugs are serious pests of pumpkins and squash. Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Large populations can cause partial wilting, and later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable. Adults are 0.5 to 0.75 of an inch long, flattened and grayish-brown. They overwinter and search for egg laying sites in late spring-early summer.
Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch.
Wingless nymphs hatch from the eggs and are similar in appearance to adults, are whitish when small, with a brown head, and grayish white when larger.
Squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense.
|Squash bug eggs. Photo by Eric Sideman.
In small plantings it is very important to scout for and squash the first adults that are appearing now.
In larger plantings clean cultivation, crop rotation and sprays for cucumber beetle generally control squash bugs.
Rotate cucurbit crops between fields as far apart as possible.
Neem products (AZA-Direct for example) have shown promise as a chemical control (see the Resource Guide to Organic Insect and Disease Management).
Pyganic 5.0 may work too. However, this is a tough pest to control with accepted organic materials.
Scout undersides of leaves for squash bug adults and eggs and get ready to treat if the copper-colored egg masses exceed one per plant.
Time squash bug sprays to kill young nymphs, which are easiest to control.
|Squash bug nymphs. Photo by Eric Sideman.
Thorough coverage is necessary.
Treat very late in the day when the flowers are closed to reduce risk to bees.
Keep headlands mowed and free of trash to reduce overwintering sites.
Clean cultivation helps reduce populations, while use of mulches and reduced tillage favors squash bug survival.
Bugs favor certain winter squash (Hubbard or marrow) over other cucurbits. One way to control adult colonization of fields in the spring is by planting a perimeter trap crop (Hubbard or marrow) 1 or 2 weeks before the main crop, and treating the trap crop just prior to main crop emergence or prior to transplanting, and 5 to 10 days later.
Pest Report - June 24, 2010
LEAFHOPPERS: Potato Leafhoppers (PLH) have made it to Maine. They are in big numbers in some fields, which may be very bad news. They are likely to be moving north so be on the lookout. They primarily feed on beans, potatoes, eggplants, strawberries and alfalfa. PLH do not overwinter anywhere near here. They overwinter way down south and leapfrog up here in mass migrations. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. Then there are a few generations over the growing season before the cold north winterkills them.
The damage from leafhopper is catastrophic. The bug sucks the juice out of the plant and injects a toxin that clogs the food conducting tissue. The symptoms look like a disease after a while, rather than insect damage, and is frequently mistaken as such. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn.
The adult PLH is very light green and wedge shaped and tiny (an eighth of an inch long). The best way to find them is to brush the plant and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are even smaller and live on the underside of the leaves. If you disturb a nymph you will see it run and it can run sideways as fast as forward. This is a clue that you have PLH and not some other less harmful leafhopper.
The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud of them, you are in trouble. Researchers have developed a threshold before treatment is recommended. Thresholds vary but here is one that is typical: Treat potatoes if 5 adults or 15 large larvae are found on 50 leaves.
Crop rotation does nothing for you since they are coming from far away. Covering your crops with a row cover would work, but these crops are not the type that is usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work as well as a pyrethrum with PBO, BUT PBO is not permitted in organic production. If you market crops as organic, be sure to use an approved brand. Use the most concentrated mix allowed. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late.
COLORADO POTATO BEETLE: Colorado potato beetle (CPB) adults are showing up in potato and eggplant crops. They have overwintered as hibernating adults and awoke in the spring to look for potatoes or eggplants, and lay eggs. The bright yellow eggs are laid in clumps with about 30-35 eggs each, generally on the undersides of leaves. As with most other insects and plants, there is a direct relationship between higher temperatures (in the range between about 55 and 90 degrees F) and faster rate of development. That includes egg laying, egg hatch, larval growth, and feeding rates. A period of cold, rainy weather slows everything down, but we can expect a surge of adults and shiny yellow eggs to appear with the next hot spell.
Scouting and Thresholds: Walk your fields NOW and look for CPB adults and eggs. A treatment should be considered for adults when you find 25 beetles per 50 plants and defoliation has reached the 10% level. The spray threshold for small larvae is 4 per plant; for large larvae, 1.5 per plant (or per stalk in midseason), based on a count of 50 plants or stalks.
Controls are needed on eggplants when there are 2 small or 1 large larva per plant (if plants are less than six inches) and 4 small larvae or 2 large per plant (if plants are more than six inches).
Potatoes can tolerate 20% defoliation without reduction in yield (or even more, late in the season). Damage to eggplant seedlings from adult feeding is often severe enough to warrant control of the adults. In potato, adult damage in rotated fields is usually not significant, so you may be able to wait until after egg hatch to kill both adults and larvae.
Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag a few of the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch.
Hatched larvae go through four stages before they become adults. In the first stage, the larvae are about the same size as the eggs and in the second stage they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the feeding damage. It’s a good idea to prevent beetles from ever reaching the fourth instar!
After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. About ten days later the next generation of adults emerges – ready to feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites. Good control in June prevents problems with CPB in August.
Crop Rotation. The single most important tactic for CPB management is to rotate potatoes or eggplant to a field that is at least 200 yards from the previous year’s fields. Since the adult that comes out of winter cannot fly well, barriers such as roads, rivers, woodlands, and fields with other crops are helpful. Rotated fields tend to be colonized 1-4 weeks later in the season. Also, the total population of adult beetles is lower, producing fewer larvae to control.
Perimeter treatments or perimeter trap cropping can be applied to potato. One approach is to plant a barrier crop between overwintering sites and this year’s crop and get it in earlier than the main crop; then control early arriving beetles.
Early planting. Green sprouting, also know as chitting, prepares whole seed potatoes to emerge rapidly, gaining about 7-10 days to harvest. This early start makes it easier for the crop to put on growth and size before CPB adults and larvae arrive. It can be combined with raised beds and plasticulture. While it won’t avoid damage altogether, it may reduce the need for insecticides. Refer to the New England Vegetable Management Guide (online at www.nevegetable.org) for more details.
Late planting. Another strategy for beating the beetle is to plant late. CPB adults that do not find food leave the field in search of greener pastures. Planting after mid- June, using a short season variety, often avoids CPB damage and eliminates the need for controls.
Straw mulch. It has been well documented that when potato or eggplants are mulched with straw, fewer Colorado potato beetle adults will settle on the plants and fewer eggs will be laid. This can be accomplished on larger plantings by strip planting in rye mulch, followed by mowing and pushing the rye straw over the plants after they emerge. For smaller plots, straw may be carried in.
Biological Control. There are numerous predators and parasitoids that attack CPB adults (a tachinid fly), larvae (12-spotted ladybeetle, spined soldier bug, ground beetles), and eggs.
Organic controls. Spinosad (Entrust) and azadiractin (AZA-Direct) are two options. Recent studies have shown very good results with spinosad, but please use reluctantly because resistance will build up in populations of CPB. The azadiractin has shown some efficacy, but neem works slowly. Generally it is used to reduce overall damage and reduce numbers but it is not a rescue treatment like spinosad is. NOTE: There is no longer a registered product for agricultural use in organic crops in the US that contains Bt tenebrionis as the active ingredient. Beauvaria bassiana (Mycotrol O) has been shown to suppress CPB populations though does not provide immediate control. And, using Beauvaria bassiana does not jive well with using crop rotation because you need the overwintered adult that remain infected with the fungus to eliminate buying the product new every year.
(Modified from the U Mass Vegetable Notes, an article by - R Hazzard; (sources include: D Ferro (UMass Amherst), J. Mishanec (NYS), J Boucher (CT), J. Whalen (DE), T. Kuhar (VA), G Ghidhu (NJ), New England Vegetable Management Guide, Ohio Vegetable Production Guide)
BLACKLEG OF POTATO (not late blight): I am getting reports of Blackleg and of course the farmers are worried it is late blight. At this time there are not any reported late blight infections in northern New England.
|Blackleg photo by David Buchanan.
Blackleg typically causes the stem of the potato to turn inky black from the potato seed piece up the stem. The leaves may then turn yellow and leaflets roll upwards and eventually the plant will wilt and die. (See the web version for a picture)
The disease is caused by a bacterium (Erwinia carotovora subsp. Atroseptica). This bacterium does not survive well in soil or really anywhere outside of the potato tuber. The chief source of the problem is planting infected seed. Warm, moist conditions favor disease development. Planting into cool, moist soil followed by warmer conditions favors Blackleg, while planting infected seed pieces into warmer soil favors seed rotting.
Managing Blackleg clearly centers on using clean seed. The level of infected seed in a lot plays a large roll, however even a low level may be a problem because the bacteria can be spread from seed piece to seed piece by seed cutting. Crop rotation is also important, as is sanitation. Rogue out any diseased plants you find.
LATE BLIGHT: As reported earlier in the week, late blight has been found in Connecticut. That still makes only isolated reports in a handful of states, but no major outbreak. Let's hope that the weather cooperates. Remember from earlier discussions, the late blight spores are killed by dry, sunny weather (see the spring issue of the MOFGA newspaper for the whole story about late blight). Last year the materials that performed the best for organic growers who kept late blight away were the copper based fungicides. Remember, if you are an organic farmer you must use a brand that meets the USDA organic standards. A few of these are Champ-WG, Cueva Fungicide Concentrate, and NuCop 50-WP.
SQUASH VINE BORER: The squash vine borer (SVB) is being caught now in high numbers in New Hampshire. If this has been a serious problem for you it is time to do some thing about it. The SVB is much more of a problem in gardens than large plantings, and much more a problem in the southern part of our region than up north.
|Diagram from University of Nebraska-Lincoln Department of Entomology.
The squash vine borer is a moth, but unlike most moths it is a daytime flyer. It is a clear-winged moth with a wingspan a bit more than an inch and has a black body. The larvae are wrinkled, whitish caterpillars with brown heads. The female moths lay eggs at the base of squash, pumpkins and gourds and the larvae burrow into the stems. They feed in the stem for about a month and the branch of the plant where they are feeding wilts and dies. With bush type squash the whole plant dies. To distinguish the damage of the squash vine borer from diseases that cause wilting, e.g., Fusarium Wilt or Bacterial Wilt, you should look for frass (caterpillar poop).
The squash vine borer overwinters as pupae or mature larvae in the soil. Adults emerge in the late spring or early summer. The warmer it is the earlier they emerge (they emerge around the time that 1000 base 50 degree days have accumulated).
Disturbing overwintering sites is the first line of defense. Till in crop debris soon after harvest. This is important for summer squash too where the early plantings of squash could be harboring larvae that may lead to a second generation of SVB that will head for your later squash.
Controlling the SVB with insecticidal materials is complicated because once the larvae borrow into the stem it is very hard to manage them. Here is a piece written by Abby Seaman, and entomologist with Cornell University, about using insecticides for managing the SVB:
Before applying any pest control product, make sure to include what you might want to use and how you intend to use it in your organic system plan and get your certifier's approval. (Caution: the use of an unapproved material can result in the loss of certification. Always check with your certifier before purchasing or using a new product or material to ensure that it is permitted for use in your organic farming system. For more information, read the related article, Can I Use This Input On My Organic Farm? http://www.extension.org/article/18321).
Spray timing is critical for effective chemical control because the larvae begin to tunnel into the stem within hours of hatching from eggs, and once inside are protected from the application. Insecticide residues must be present at egg hatch so larvae contact or feed on residues as they enter the stem. Moth flights (and egg-laying) may be predicted by degree-day accumulations as described above or monitored by pheromone traps. Small wire cone traps, nylon mesh Heliothis traps, and Unitrap bucket traps have been found to me most successful for monitoring squash vine borer (Jackson et al. 2005). Traps and lures may be purchased from Great Lakes IPM (www.greatlakesipm.com/) or Gemplers (www.Gemplers.com).
Several insecticide active ingredients approved for organic production are labeled for use against squash vine borer including azadirachtin (neem), neem oil, kaolin clay, geraniol, thyme oil, pyrethrins, and spinosad. Of these, efficacy information is currently available only for spinosad. Trials in Connecticut showed that four weekly applications of spinosad applied during the moth flight resulted in control levels similar to a conventional pyrethroid insecticide.
Stem injections of Bacillus thuringiensis (Bt) are frequently recommended for squash vine borer management, especially for organic gardeners. Trials in South Carolina compared spray application and stem injection of commercial formulations of Bt with a conventional insecticide and an untreated control (Canhalil and Carner 2006). The injection and spray application methods produced similar results, and the Bt treatments provided control similar to that of the conventional insecticide. Note that Bt does not appear on the list of active ingredients currently labeled for use against squash vine borer.
Good morning growers,
I just received news that late blight was found in Connecticut. Here is what I know:
Late blight has been confirmed for the first time in New England (Thursday morning, 17 June 2010), on tomato plants in a backyard garden in Cheshire, CT (New Haven County). The tomato plants were grown from seed and the grower actually did not have late blight last year. Thoughts are that it could have been infected from nearby greenhouse, bedding plants or market farm neighbors. I am sure we will hear more.
Cooler, moist conditions over the past week produced favorable conditions for late blight to spread. The hot, sunny days yesterday and today put a stop to any spreading (sunlight kills the LB spores). But, U Mass reports conditions warrant starting preventative fungicides in the Connecticut Valley, and in eastern and southeastern MA, although north central and Berkshire locations down there are ok for now. I have not heard that yet about northern New England, but I will if we reach those conditions. Given a confirmed case in southern New England, we should raise our alert level and continue to watch for and rogue out potato volunteers, and continue to scout potato and tomato fields for symptoms. It is time to start scouting the market for formulations of copper that are allowed (Champ WG, and NuCop 50 WP, for example) just to be ready. I am not worried yet.
MOFGA Organic Crop Specialist
Pest Report - June 18, 2010
ONION THRIPS (Thrips tabaci). Onion thrips are active now and if they have been a problem for you in years past it is time to start scouting for them. They are very tiny and easily overlooked until the onion plants start showing leaves that look as if they have been rasped. In fact they have. The thrips feed by using their moth parts to rasp and pierce the onion leaves, releasing juices for them to feed upon. If the population of thrips is large you will see silvery patches on all the young leaves and when really bad the whole field will look white and silvery and the leaves wither. Obviously onion yields can be greatly reduced because the onion plants lose food and water through the damaged tissue.
|Illustration from NC State University.
Onion thrips hide between the leaves at the base of the onion plant. I find the best way to find them is to pull up a plant and hold it upside down over a white sheet of paper and pull apart the leaves as you shake gently. Even when they are walking about on the paper you will still need to look hard to see the thrips. My eyes are not that good and I need a hand lens to even spot them. The immature thrips are white to a pale yellow, elongated with very short antennas and dark eyes. Remember, tiny. The adult is tiny too, but it has wings. Thrips' wings are unique. They are fringed with hairs. Thrips are very poor fliers, but they do fly when disturbed and get blown in the wind easily. Keep in mind that this means thrips will be blown to new fields downwind. Adults are pale yellow to dark brown.
There are many generations per season and they can be very quick in warm weather. Also, parthenogenesis is common, meaning females that cannot find males produce progeny all by themselves. Each female can produce up to 80 eggs, which tells you that the population can explode quite quickly under good conditions. Good conditions are warm and without heavy rains. Heavy rains wash the weak insect off the plant.
Growers can simulate heavy rains with heavy overhead irrigation. As well as disturbing the insect the extra water will help the rasped onions. Extra fertilization will help too.
Thrips survive in onion debris so clean up after harvest. I have heard that inter-cropping with carrots confuses thrips.
If the natural enemies or the cultural practices fail to keep thrips populations down then you may need to turn to a pesticide. Remember, thrips are often around in small numbers that can be tolerated. IPM practices recommend an economic threshold of an average of 3 thrips per green leaf. When scouting, sample about 50 plants around the field from at least 10 different locations in the field and then figure the average per leaf. Entrust is the most common recommended material. Follow the label instructions and be sure to spray into the leaf axis.
FOUR-LINED PLANT BUG (Poecilocapsus lineatus). The four-lined plant bug is a general feeder that attacks many kinds of crops and weeds. Basil and mint are favorites but it will also feed on hundreds of other species. The damage is sometimes confused with disease symptoms. Both the nymphs and adults suck plant sap. Their feeding leaves tiny spots about the size and shape of flea beetle feeding holes but the plant bug does not completely puncture the leaf and so there is a sort of window look to the spot. There is a toxin in the saliva of the plant bug that is meant to digest the leaf tissue. This leads to, in addition to the spots, distorted leaves that may turn dark brown and curl up and eventually fall off, hence the confusion with disease. Also, since the plant bug is very flighty and drops off and falls to the ground quickly when disturbed it is common that the pest is not seen, i.e., just the damage is seen.
|Image from University of Minnesota.
The four-lined plant bug adult is greenish yellow with four black lines running longitudinally down its back. The nymphs are bright red with tiny black beginnings of wings. For some good pictures of adults, nymphs and damage see:
The four-lined plant bug lays banana shaped eggs in the fall in slits in the plant stem. The eggs overwinter and hatch in mid spring and the nymphs begin feeding. It takes about a month and a half for the nymphs to develop into adults. The adults feed for a month or so and then lay eggs. The adults do not overwinter and there is just one generation per year.
For most vegetable crops the damage is tolerable. Herbs may be ruined. Insecticidal soap and summer oils have proven useful. Some fact sheets say you can scout for and destroy the eggs in the fall, but that seems unreasonable. I've never even have seen them.
CUTWORMS. Cutworms are still a real challenge for some growers, especially for small transplants and carrots and onions. Cutworms are the caterpillars of a few different species of night flying moths. Some of the species fly in very early in the spring and others arrive in the fall. They lay eggs at the base of plants (weeds and cover crops as well as your cash crop). The eggs hatch into tiny, dark gray, greasy caterpillars that feed at night. Some species just simply cut off your plants just about at ground level. Other species climb up and cut off leaves or eat notches out of them. The caterpillars can be found in the soil by digging around near the damaged plants. They curl up into a "c" shape when you handle them.
|Image from University of Minnesota.
The big problem is you never know whether it will be a problem or not. On a small scale, Dixie cups with the bottoms cut out placed around a transplant make a good barrier.
One method that works on a large scale but is usually not practical is to starve them out. If you can keep a field completely free of ANY growing plants (weeds or crops) for a few weeks after they hatch then they will starve and die.
I have received good reports about making bait from wheat bran, a Bt solution and molasses and then sprinkling it or making patties and putting the patties along the row of effected crops. This year I tried using alfalfa meal instead of bran and I really think it works. No, I don't have a specific recipe. This idea is a copy of baits that were recommended fifty years ago, but then with toxins way to frightening to mention. I suggest you make the most concentrated solution of the Bt allowed on the label. A solution of Entrust would work too. Make the solution of Bt and molasses and then add the bran or alfalfa meal to make it damp. Put it out in the evening because the cutworms feed at night and the Bt breaks down quickly in sunlight.
I have also heard very good reports from folks who have used parasitic nematodes. The best results for cutworms is achieved when a combination of two types of nematodes are applied in a mixture because the different species work different levels in the soil and attack the cutworms both while they hide deeper in the soil during the day and when they move up at night. A mixture of Heterorhabditis bacteriophorea (Hb) and Steinernema carpocapsae (Sc) has essentially eliminated cutworm problems for some of our growers. The nematodes are usually shipped on a sponge ready to mix with water and apply to the soil. It is important not to let the soil surface dry out after application. A few suppliers of these insect-attacking nematodes are The Green Spot (www.greenmethods.com), IPM Laboratories (www.ipmlabs.com), and ARBICO (www.arbico.com). It may be too late this year for nematodes to help, but remember for next year.
Pest Report - June 8, 2010
STRIPED CUCUMBER BEETLE (Modified from article in Mass. Veg. Notes written by Ruth Hazzard & Andrew Cavanagh, University of Massachusetts, updated for 2010.) Striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris in field edges, and with the onset of warm days and emergence of cucurbit crops, move rapidly into the field. I am just receiving reports that the pest is appearing in south/central Maine. Densities often are very high, especially in non-rotated fields or close to last year’s cucurbit crops. Management cannot wait because adult beetle feeding on seedlings (cotyledons and young leaves) is the most serious, and can cause stand reduction and delayed plant growth. Also, the striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt, and this may be more damaging than direct feeding injury. Crop rotation, transplants, and floating row cover are cultural controls that help reduce the impact of cucumber beetles. By far, floating row covers offer the best results. You must get the row cover on at transplanting or seeding. Early management is important to avoid early season infection with wilt. Cucurbit plants at the cotyledon and first 1-4 leaf stage are more susceptible to infection with bacterial wilt than older plants.
|Striped cucumber beetles are our most serious early-season pest in vine crops.
Perimeter trap cropping gives excellent control with dramatic reduction in pesticide use (see following short article).
Beetle numbers should be kept low, especially before the 5-leaf stage. Scout frequently (at least twice per week for two weeks after crop emergence) and treat after beetles colonize the field. Early spot treatments of field edges can be helpful. The threshold depends on the crop. To prevent bacterial wilt in highly susceptible crops, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants. Less wilt-susceptible crops (butternut, most pumpkins) will tolerate 1 or two beetles per plant without yield losses. Spray within 24 hours after the threshold is reached. Proper timing is key.
OMRI-listed insecticides available for use in striped cucumber management include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). In 2009 spray trials comparing these three products at the UMass Research Farm, kaolin was the most effective in reducing beetle numbers and feeding damage. There was a trend toward Surround WP being more effective when Pyganic or Entrust was mixed with it, but never significantly better than Surround alone. Other studies have shown more efficacy from pyrethrin and spinosad. Remember, Surround should be applied before beetles arrive because it acts as a repellent and protectant -- beetles do not “recognize” the plant and so do not feed -- not a contact poison. With direct-seeded crops, apply as soon as seedlings emerge if beetles are active. Transplants can be sprayed before setting out in the field.
I just heard from a grower who tried out a vacuum yesterday and reported that it seemed to work well. He suggests using a vac with a low setting and/or a broad nozzle so that you don't damage plants. Also, do this earlier in the morning when they are sleepy and slow and be sure to look in their hiding places under the plants.
PERIMETER TRAP CROPPING FOR CUCUMBER BEETLE MANAGEMENT (Reprinted from Umass Veg. Notes)
Over the past years, you have probably heard a lot from us about perimeter trap cropping to manage striped cucumber beetle in cucurbit crops. The system has proven itself as an effective, cost-saving method for managing this pest. Systemic or foliar insecticides in the trap crop border are effective in halting the beetles in the border and protecting the main crop. PTC systems can reduce insecticide use by over 90% if implemented correctly, but this is not the only benefit. By spraying only the border of your crop you’re leaving the main part of the field as a refuge for pollinators and natural enemies of insect pests. Leaving the main crop unsprayed may also help to delay the development of insecticide resistance in the striped cucumber beetles – a few beetles will always bypass the border, and thereby escape selection for resistance. The first trap crop that we looked at was Blue Hubbard, but many growers told us that Blue Hubbard is difficult to market and other border trap crops were needed. We evaluated buttercup and kabocha squash as alternative border crops, and they worked just as well as Blue Hubbard. Markets for these crops are strong. Any Cucurbita maxima variety is likely to be very attractive. This species includes many giant and specialty pumpkin varieties; the only one we do not recommend as a border crop is Turk’s Turban because unlike most C. maxima varieties it is highly susceptible to bacterial wilt which is vectored by the beetles. You can even plant a border of mixed C. maxima around your butternut squash, acorn squash, and other winter squashes that are C. pepo, or C. moschata types. This will provide you a wide variety of interesting squash to market. We’ve tested this system extensively and found that as long as the trap crop border is planted on good land and remains intact the system works remarkably well. In most cases, growers who use this system never need to apply insecticides to their main butternut crop at all. In Connecticut, they’ve found the system to work equally well with cucumbers and summer squash. Zucchini tends to be more attractive than summer squash, and some varieties such are so attractive that they could be used as a trap crop. We’ve also seen PTC work well in pumpkin crops, as long as the pumpkins in the main crop are C. pepo and not C. maxima. Remember, many giant and specialty pumpkins are actually C. maxima species, and would make good trap crops. On organic farms, growers often treat the main crop with kaolin clay (Surround WP) which serves as a repellent. For transplants, using this before planting is very efficient and lasts for a week or so if there are not heavy rains. Spinosad or pyrethrin could be used in the border. Every year we talk to more growers who adopt this system. The reduction in pesticide costs can be dramatic, and more than offset the small amount of time and care it takes to plant and treat a solid perimeter trap crop. If you would like to try this system and have any questions, or just want to find out more about how it works, please call Andy Cavanagh at 413-577-3976.
MEXICAN BEAN BEETLE: PLAN AHEAD FOR BIOLOGICAL CONTROL (Reprinted from Mass. Veg. Notes, written by Ruth Hazzard). If Mexican bean beetles have historically been a problem on your farm, you will very likely see them again this year. They may be pests on snap beans, soybeans, and lima beans. While they are not a pest on every farm, some farms report significant damage from these pests and have to take action to prevent crop loss. Using biological control can reduce the need for insecticides. Mexican bean beetle (MBB) adults are coppery brown with black spots. They look very much like large ladybeetles and in fact are closely related – but unlike lady beetles they feed on leaves, not other insects. Adults lay yellow-orange egg masses on the underside of bean leaves. These hatch into bright yellow, spiny oval larvae, which feed, molt several times as they grow, and pupate on the underside of leaves. Feeding damage from adults and larvae can reduce yield and injure pods if numbers are high. There are several generations per season, often with increasing populations in each generation. Pediobius foveolatus is a commercially available biological control agent for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among New England growers who have tried it. (Pediobius is pronounced “pee-dee-OH-bee-us”). It is mass-reared and sold by the New Jersey Dept of Agriculture and is also available from other beneficial insect suppliers. This small (1-3 mm), non-stinging parasitic wasp lays its eggs in Mexican bean beetle larvae. Wasp larvae feed inside the MBB larva, kill it, and pupate inside it, forming a brownish case or ‘mummy’. About twenty five adult wasps emerge from one mummy. Control continues and in fact gets better as the season progresses and successive generations of the wasp emerge and search out new bean beetle larvae. Planning 2-3 releases at 7-10 day intervals will help ensure good timing. and coverage on several plantings. This makes it well suited to our succession-planted snap bean crops. After a release in the first plants, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies. As with any biological control, make releases as soon as the pest is present – not after it has built up to damaging numbers. The New Jersey Dept of Agriculture Beneficial Insect Rearing Laboratory recommends two releases, two weeks in a row, coinciding with the beginning of Mexican bean beetle egg hatch. Wasps will lay their eggs in larvae of any size, but it is best to target the newly-hatched young MBB larvae. This will give control before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for the first hatch of eggs into larvae. If in doubt about the timing of the hatch, release as soon as you see the eggs – if you wait for the larvae you may be playing catch-up. The release rate should be at least 2000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more. The 2009 cost from NJDA is $40 plus shipping for 1000 adults, or $20 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge. Order adults if you already have MBB larvae in the field. Ship for overnight delivery. Instructions for handling and release will come with the wasps. Wasps reproduce in the field and will still be around when the second generation of MBB hatches out. Thus, it should not be necessary to make more than two releases. Like beans, Pediobius wasps are killed by frost. Plan ahead by contacting a supplier to inform them of your expected release dates and acreage. Contact information for New Jersey source: Tom Dorsey, 609-530-4192; address; NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Trenton, NJ 08628. http://nj.gov/agriculture/divisions/pi/prog/beneficialinsect.html. Pediobius is also available from the following suppliers: Green Spot Ltd., NH., www.greenmethods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Network (TN), 615-370-4301, http://www.biconet.com/. If you would like assistance in using these biocontrols in your bean crops please call the UMass Extension Vegetable Program at 413-577-3976 or 413-545-3696 or email at email@example.com. --
|Mexican bean beetle larva (above) and adult (below).
CUCUMBER BEETLES ON MY POTATOES? No. Those are not cucumber beetles. Potatoes, tomatoes and sometimes eggplants are attacked by this pest that only superficially looks like a cucumber beetle. This is the Three-Lined Potato Beetle. The adult of this pest is about the same size as a cucumber beetle but has a reddish head and a thorax with two dark spots. The wing covers are dark yellow with three black stripes. Its favorite food in my experience is tomatillo.
The Three-Lined Potato Beetle overwinters as an adult and wakes early in the spring. They are there waiting for you to plant your solanaceous crops. The females soon begin laying eggs that hatch in about two weeks to larvae that look a bit like Colorado potato beetle larvae, except these critters have the endearing practice of carrying a small pile of their own excrement on their back. The larvae mature in about two weeks. There are probably two generations per year.
On most crops the level of the pest does not warrant control. If this pest has been a problem in the past, floating row covers will help you avoid the overwintering adults and that should get you by. Hand picking will work on small plantings. Pyganic and Entrust may offer some relief. Rotenone works well, BUT REMEMBER THAT THERE ARE NO ROTENONE FORMULATIONS THAT MEET ORGANIC STANDARDS.
LATE BLIGHT UPDATE/TOMATO SPOTS. At this time late blight is not reported in New England. There were reports in more southern locations, e.g., PA, but that seemed to be a localized event and not related to anything that is moving towards us. There have been no new reports recently. Of course, I will immediately get the word out when I hear about anything.
|Photo by Cheryl Smith, University of New Hampshire.
In the mean time, you should learn to recognize some other tomato problems. I have not heard about or seen these here yet either, but these are regular problems that will be here soon. Be ready and don't jump to the conclusion that you have late blight. Learn to recognize that too. If you are reading this as an email, you may want to go to the on-line version that has pictures. That is posted a few days later than the email goes out.
The three most common problems with tomatoes grown in the field in Maine are Early Blight, Bacterial (Spot and Speck) and Septoria Leaf Spot. It is early, but it is time to start looking if you want to get some control on them.
-Bacterial Speck starts as dark brown to black spots on leaves that later develop yellow halos around the area effected. On the fruit black specks develop that rarely get larger than 1 mm . Bacterial Spot starts as brownish, circular spots that may become as large as 3mm and irregular. The diseases may be seed borne and may be carried over in weeds. High humidity and low temperatures favor bacterial speck.
|Early blight on tomato plant (above). Septoria leaf spot on tomato plants (below).
-Early blight of tomato is caused by fungi and starts on the lower leaves as small circular spots that have a target appearance of concentric rings. Leaves develop yellow blighted areas as the spots enlarge. Later the tomato fruit may rot on the stem end. The disease is carried over on tomato residue in the soil and can be seed borne.
-Septoria Leaf Spot is a fungal disease that starts as spots on the lower leaves that have a dark brown margin and a tan center, and no target appearance. Rapid defoliation can occur.
Crop rotation is the first line of defense from these problems. Sanitation is important. Do not grow tomatoes near cull piles of last year's crops. Trellising, staking, cages, etc help but remember to disinfect if they were used last year (a 12X dilution of household bleach is effective). Prune off diseased lower leaves, but it is especially important to disinfect tools if the problem is one of the bacterial diseases. Avoid working in the crops when they are wet. Scouting is going to be important this year. With wet weather, start early and if you decide to use a material, copper is probably the one most effective for us organic growers. If you decide to do it, start at the first sign of problems and you need to keep the new tissue covered. Still, because of problems with the way inert ingredients are regulated in the NOP Rule and the changes in the way EPA categorizes inert ingredients, Champ WG is one of the very few permitted formulations of copper for certified growers. Be sure to check with your certifier if using something other than that.
Late Blight Update - May 25, 2010
Late blight has been confirmed south of us in PA and MD. MOFGA Organic Crop Specialist Eric Sideman does not believe this raises risk for us in Maine because the weather has been very warm and dry, and the late blight spores could not make it this far in this kind of weather. With luck, we will not experience damp cloudy weather that is so good for late blight spore travel. The source of the late blight in PA and MD has not been confirmed. It seems like a local problem, unlike last year. Let's take it as a warning and keep our eyes open. Be vigilant but not full of panic. Please scout sprouting potatoes, and young tomato plants for any signs of late blight. Pull volunteer potatoes. If you see something suspicious you can send a picture to Eric via email at firstname.lastname@example.org, or contact your local Cooperative Extension office.
Pest Report - May 20, 2010
COLD-THEN HOT-THEN VERY COLD: This season has been a challenge for growers of fruits and other perennial crops. The very warm weather early in the spring pushed all these crops ahead by at least two weeks. That could be good, but more likely is bad; and it was bad.
Crops that normally can tolerate the typically cold weather of early May were not able to handle it at this advanced stage of development. And it was very cold. The week after Mothers day, I saw 24 degrees F here in the south, and heard 21 degrees F in central Maine. That killed much of the apple crop and most of the strawberries that were not protected with covers or irrigation.
That problem is a bad memory now and most of us want to move on. Of course, the best approach would be to learn from it before moving on. Learn how frost kills, what temperatures are killers, and methods of protection. Learn for next year, but also, in reality, we are not out of the woods yet. Frosts in Maine are not uncommon even now and into the first week of June.
Download a great article about frost and fruit with a table of killing temperatures for different fruits at different stages:
FLEA BEETLES IN BRASSICAS: Flea beetles are busy feeding in spring plantings of brassica crops in Massachusetts. Numbers are likely to rise in coming weeks here in Maine as beetles move out of field borders where they spent the winter. Crucifer and striped flea beetles feed on Brassica crops as well as weeds that are in the same family, such as yellow rocket or wild mustard. [It is a different species of flea beetles that feeds on the tomato family of crops. This is important information when planning rotations of potatoes, tomatoes with Brassica crops or cover crops].
The crucifer flea beetle (Phyllotreta cruciferae) is uniformly black and shiny, about 2 mm in length, while the striped flea beetle (Phyllotreta striolata) has two yellow stripes on its back. Flea beetle adults feed on leaves and stems, resulting in numerous small holes, or ‘shot-holes’. Eggs are laid in the soil starting in late May, and beetle larvae feed on roots. The non-waxy greens (arugula, bok choi, tatsoi, mustard, Chinese cabbage, komatsuna) are preferred to the waxy cabbage, kale and collard types of brassicas. In brassica greens, beetles feed on the whole surface of the leaf, and will continue feeding from the seedling stage until harvest. Waxy crops are most susceptible at the cotyledon and seedling stage and feeding is more limited to leaf margins on older plants. Some crops simply out grow the beetle pressure and the damage can be tolerated. No damage can be tolerated in crops such as arugula.
To reduce and delay flea beetle invasion of spring crops, move them as far away from the fields that were used for fall Brassica crops as possible. Beetles overwinter in field borders near last year’s crop. Planting the same crop close by to where it was last year ensures a high population in the spring. The same could be true if you have fields full of mustard weeds.
One of the best ways to protect Brassica crops from flea beetles is to place a floating row cover over the bed or row. It is critical to seal the edges immediately after seeding or transplanting, because Brassica seeds germinate quickly and beetles rapidly find the cotyledons. Flea beetles can fit through extremely tiny cracks. Edges of the cover must be sealed on all sides using soil, plastic bags filled with soil, or some other method.
Spinosad (Entrust is organic formulation) is proving to be effective in suppressing flea beetles and reducing damage. Pyrethrin (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. Yet some growers have reported a good knockdown with this product. You can spray the Pyganic right through the floating row covers and knock down any flea beetles that may have gotten inside.
CABBAGE AND ONION MAGGOT: (Reprinted and modified from Umass Veg Notes). Onion maggot (Delia antiqua) and cabbage maggot (Delia radicum) flies look nearly identical but are likely to be found only on or near their host crop. Cabbage root maggot attacks all types of Brassica crops, while onion maggots are highly specific for the onion family including onions, garlic, leeks, chives, and shallots. A good indicator of the start of cabbage root maggot flight is blooming of the common roadside weed, yellow rocket. This weed has been blossoming for a few weeks in southern Maine.
|Onion maggot damage. Photo by Eric Sideman.
Life cycle: Onion and cabbage maggot flies spend the winter as small brown pupae in the soil. Adults emerge in spring and adults can travel considerable distances in search of host plants (1/2 to 1 mile). Cabbage root maggot flies are rather delicate, hump-backed gray-brown flies, about 5-7 mm long. Onion maggot flies are very similar. Female flies seek out their host crop to lay eggs at the base of the stem. Cool, moist soil conditions favor survival of the eggs, and soil temperatures over 95 F kill them. When the soil temperatures in the upper half to 1 inch are high (>100 degrees F) that soil temperature itself then provides control. It is possible we’ve reached these conditions in April this year, but this would only help if eggs were already present. This is the reason these pests are much more of a problem in the spring and summer generations of the pest are rarely noticed.
When eggs hatch, larvae feed on roots and can cause complete destruction of the root system. In crops such as broccoli or cauliflower the first sign of a problem is wilting of the plant on sunny days and yellowing of outer leaves. Later, plants collapse, wilt down, and die. If you pull one up you will see that the reason it is wilting is the roots are gone. You may find the legless white maggots feeding, or the small brown, oblong pupae. In Brassica root crops such as turnips, radishes and daikon, feeding tunnels make the root unmarketable.
In onions, newly hatched larvae crawl behind the leaf sheath and enter the bulb, and feed on the roots, stem, and developing bulb. Feeding damage also encourages entry of soft rot pathogens.
Avoiding damage by later planting. The first flight and egg-laying period is generally most intense in the first half of May, depending on accumulated growing degree days – thus, it will vary with the season and location. After the first flight is over, and as soils heat up, fewer eggs are laid and those that are laid are less likely to survive. I have observed that in most years that Brassica transplants set out after the flowers fall from forsythia did not suffer damaging infestations of cabbage maggots. In cooler areas of the state, however, scouting has sometimes found damaging levels into June. Each season will be different – and this year everything is early. It is impossible to name a consistent and reliable date after which it is safe to plant onions or cole crops, but late May into June will likely be safer than the first half of May. So, if you are seeing damage, there is still time to do another planting of onions and be less at risk. And, there is time for many more plantings of brassica crops.
Monitoring. Flies are attracted to bright yellow colors. Yellow sticky cards (3X5 inches) are inexpensive and easy to use; attach them with small wire stakes and place near the soil. Check and change traps twice weekly to record changes in fly activity. (sources: Great Lakes IPM, Gemplers)
Using Growing Degree Days. The beginning and peak of each fly generation can be forecasted using degree day accumulations. Most growing degree day information for
plants and insects is based on a base temperature of 50 F, but maggot flies are active at a lower base temperature of 40 F. For more information on using growing degree days, go to http://www.umassvegetable.org/ and look at the May 6, 2010 issue of the Umass Newsletter.
Floating row covers provide an effective barrier against these pests. Place the cover on as soon as the transplants are set. Use in a rotated field, as flies overwinter in soil after late season crucifers and could emerge under the cover if the same field has spring brassicas. Replace cover after weeding operations. As soil temperatures rise, the first flight ends and crops grow large, covers can be safely removed.
Crop rotation contributes to keeping populations low; greater distances are more effective. Fall tillage to bury crop residues and to expose over-wintering pupae is also important. For onions, bury or haul away onion cull piles. Rotting onion smell attracts the onion maggot fly. In an vigorous Brassica crop, cultivation that brings soil up around the stem may help encourage formation of adventitious roots from the stem, which can help compensate for root loss even if maggots are present.
Naturally-occurring fungal diseases occasionally will reduce onion maggot numbers significantly, particularly when flies are abundant and relative humidity is high. During a fungal epidemic dead, diseased flies, can be seen clinging to the highest parts of plants along field edges. Predaceous ground beetles, which eat onion maggot eggs, larvae and pupae, can also be important in reducing maggot numbers.
Nematodes for biological control. One alternative method that has shown promise but has not been widely field-tested is soil application of entomopathogenic nematodes, especially Steinernema spp. Steinernema feltiae has been found to be more effective compared to other Steinernema or Heterorhabditis species in attaching to and penetrating cabbage root
maggot larvae at low temperatures (10C) which is an important trait for use in spring when soils are cold. Common application methods include suspension of nematodes (infective juveniles) in water and application of water to transplants prior to setting in the field (as a spray or soaking drench), in transplant water used in the water wheel transplanter, as a drench after transplanting, or a combination of pre-plant and post-plant applications. Rates of 100,000 to 125,000 infective
juveniles per transplant have been shown to be needed to achieve reduction in damage.
Some Beneficial Nematode Suppliers:
The Green Spot: 603-942-8925 or www.shopgreenmethods.com
IPM Labs: http://www.ipmlabs.com 315 497 2093
Arbico Organics: http://www.arbico-organics.com +-800 827 2847
Griffin Greenhouse Supplies: 978-851-4346 or www.griffins.com
Integrated Biological Control Systems: 888-793-4227 or www.goodbug-shop.com
Koppert Biologicals: 800-928-8827 or www.koppert.com
--R Hazzard. References: Network for Environment and Weather Applications (NEWA) of NYS IPM Program; Univ of Wisconsin-
Minnesota Degree Day Calcuator (http://www.soils.wisc.edu/asigServlets/asos/SelectDailyGridDD.jsp); Ontario
Ministry of Agriculture, Food and Rural Affairs online fact sheet ; Schroeder et al 1996, Journal of Economic Entomology
89:1109-1115; Chen et al, 2003, BioControl 48: 713–724
WIREWORMS: (Reprinted from Becky Sideman's UNH Vegetable Newsletter). I have gotten quite a few questions about problems with wireworms recently. Wireworms damage root and tuber crops such as potatoes and carrots by tunneling, causing unsightly holes as well as providing an entry point for pathogens. Young seedlings with small root systems can be weakened or Life of the Wireworm. Wireworms are the larvae of click beetles (family Elateridae). There are many species of wireworm. The larvae have slender, hard, ≤ -1 inch long bodies that range from tan to orange to brown in color. The larvae pupate in the spring, and the adult beetles emerge and are active in the summer. The adult beetles are not typically pests. Female click beetles lay eggs during May and June. They lay eggs in the soil, primarily in weedy or grassy fields. The eggs hatch in 3-4 weeks, and the larvae then look for food. The larvae can live for several years, depending on the species, availability of food, temperature, and soil moisture. Because eggs are typically laid in grassy fields, wireworm problems are usually most severe in fields that were recently sod. However, because the larvae can live for many years, problems can persist in fields that have not been sod for some time. And grassy cover crops can attract the adults for egg laying. Wireworms are often more prevalent in moist areas of fields, and in areas with high organic matter.
What they Eat. Wireworms are omnivores. They feed on the roots of grasses or weeds and on other soil insects. It is hard to starve wireworms out of a particular area, because of their diverse diet. Crops that tend to increase wireworm populations include potato, carrot, sweetpotato, small grains (wheat, barley), onion, beet, and clovers. A clean (non-weedy) alfalfa crop can reduce populations. This may be in part because of alfalfa's deep root system reduces soil moisture, making the environment less favorable for the larvae.
Minimizing Damage. Rotation into alfalfa or crops that are not preferred can reduce wireworm populations. Avoid planting highly susceptible crops such as potato and carrots into sites with a high potential for damage, such as fields previously planted to grass sod, pasture or small grains, or fields with a prior history of wireworms. The edges of fields (near sod) can also be a problem, because the larvae can move through the soil in search of food. Baits can be used to determine wireworm pressure prior to planting a susceptible crop. This can be done by placing carrots or potatoes in a softball-sized hole about 4-6‰ deep, covering with loose soil, and then covering the area with a piece of black plastic to warm the soil. Wait 4-7 days, and dig up the bait to check for the presence of wireworms before planting. On small scale plantings this baiting system can be used to reduce numbers in gardens. Another version of this method involves burying a fist-sized clump of corn, wheat, or rolled oats. It may also help to harvest crops as soon as possible. Some reports indicate that the wireworms seek out the moisture in potato tubers if soil conditions become dry, and wireworm damage increases over time in potato crops left in the ground.
BACTERIAL CANKER OF TOMATOES: I have heard of a few instances of bacterial canker in hoop house tomatoes this year. Please get in touch with me if you see this or think you may have it in your early tomato plantings.
Bacterial canker is a sporadic disease but devastating when it occurs. It could be spotty even within a planting. The symptoms of canker is a systemic wilt first appearing as downward turning of lower leaves with upward curling of the leaflet edges. Leaflets wilt often only on one side of a leaf. Marginal necrotic leaf lesions are often the first outward expression of bacterial canker.
It is primarily carried from year to year on contaminated seed, soil with infected tomato debris, stakes with debris, etc. and is spread during the season by splashing water, contaminated equipment and workers hands.
Clean seed is the first defense. This is the job of the seed company. If you have had the problem before, then be sure to use and/or sterilize soil mixes, stakes, pots, etc. Pruning tools should be sterilized between plantings. If you have bacterial canker in a field, then the debris should be incorporated into the soil to encourage decomposition. Crop rotation is recommended.
Remember, the pest report often has pictures but to view them you need to go to the MOFGA website (mofga.org) and under publications you will find the Pest Reports.
ASPARAGUS (Modified from UMass. Veg. Newsletter)
Frost: One of the very first questions I received when I began working for MOFGA many, many years ago turned into an argument. Not a good start, huh?. The guy who called would not believe me that asparagus is frost sensitive. His spears had turned dark, wrinkled and water-soaked and I don't know if I ever convinced him. Perhaps he is reading this.
Asparagus, despite its status as a primo early season vegetable, is highly sensitive to frost, ranking alongside cucumber, snap beans, eggplant and tomatoes in the ‘most susceptible’ category. The early hot spell this year moved everything, including asparagus, ahead by weeks. It made some growers in-the-know uneasy as spears pushed out of the ground, only to face the a string of cold nights and snow. There is still a good chance of frost though you would not believe it since it was near 90 yesterday!
When frosted, spears appear slightly darker green, water-soaked and break off easily. Thawed spears become mushy. Soft-rotting bacteria can enter the damaged tissue. New spears take several more days to emerge, but will. Temperatures below 33 degrees Fahrenheit may damage the spears.
Beetles: Common asparagus beetles tend to arrive in mid May (I bet this year earlier). The spotted asparagus beetle generally becomes active somewhat later in the spring, and in my experience is less common (I guess with the names that is not a surprise). These two beetles are closely related and have similar life cycles but it is the common asparagus beetle that is most damaging to the cut spears.
|Asparagus beetle eggs. Photo by Eric Sideman.
Common asparagus beetle (Crioceris asparigi) is blue-black, shiny, smooth and about 6 to 9 mm (1/4 inch) long, with three large yellow, squarish spots with red margins along each wing cover. Eggs are black, laid standing on end in rows along the spears, and hatch in 3-8 days. Larvae are wrinkled, plump, hump-backed, and dull gray with black head and legs. They grow up to 1/3 inch. These larvae feed in spears and in ferns. The larvae do the most damage, and eggs and larval damage makes spears unmarketable. Larval feeding can cause severe defoliation and weaken the stand. When full grown, larvae drop to the soil and pupate underground. New adults emerge in July, feed in ferns, and by September are looking for overwintering sites.
Spotted asparagus beetle (Crioceris duodecimpunctata) is reddish orange or tan, with six black spots on each wing cover (hence its other name, 12-spotted asparagus beetle). Eggs are greenish, glued singly on their sides to leaves. Eggs are laid on fronds, not on spears. Larvae are similar to those described above, but are orange colored, and feed almost entirely inside the berries so they affect seed production but do not hurt the plants.
Winter habitat: Both species spend the winter as adult beetles either in field borders or within the asparagus field. Sheltered sites such as under bark or in the stems of old plants are preferred. Some burrow into the soil.
|Asparagus beetle larva.
Photo by North Carolina Cooperative Extension.
Scouting: Early in the season, look for adult beetles, for feeding damage and for eggs laid on spears. Michigan State recommends a treatment threshold of 5-10% of the plants infested or 1-2% of the spears with eggs or damage.
Cultural controls: During harvest, you can greatly reduce the population by harvesting ALL of the spears every day.
Pick the field clean to reduce the number of stems where eggs will survive long enough to hatch or larvae can feed and grow up into summer-generation beetles. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter, by disking lightly (avoid crown damage) or burning crop stalks and fronds. Maintaining a clean environment in the fall will force beetles to seek shelter outside the field or burrow in the soil, where many predators reside.
Biocontrol: The most important natural enemy of Common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. Wasps kill eggs by feeding on them (sucking them dry), and also lay their own eggs
|Asparagus beetles. Photo by Eric Sideman.
inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs killed by feeding and half of the surviving larvae parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.
Monitoring and chemical control: Scout fields regularly. You may want to treat spears if >10% of the plants are infested with beetles or 2% have eggs or damage. The daily harvest makes treatment difficult because few want to spray anything close to harvest time. Organic options on spears include Surround WP as a repellent, Pyganic EC5.0, or Entrust.
R Hazzard. References: Handbook of Vegetable Pests by John Capinera; 2008-2009 New England Vegetable Management Guide; Eric Sideman, MOFGA; Brian Caldwell, Cornell University
Raising seedlings in a "sterile" mix such as Pro Mix is easy. These mixes are called sterile, however they are not really sterile. On the other hand they are called sterile by growers because they don't have plant pathogens in them, and that beats my home-made mix. These "sterile" mixes are mixes of pathogen free materials such as peat, perlite, vermiculite with synthetic and very available sources of plant nutrients added in just the right amount to get newly germinated plants off and growing. Organic growers do not have the option to use these mixes. We either purchase mixes that are generally based on compost, or mix up our own. Seedling problems are much more likely in organic mixes because of the possibility that the compost may be carrying plant pathogens. In addition, it is much more difficult to predict the availability of nutrients from natural sources because of how biological activity is greatly affected by temperature, moisture and other factors. Many commercially available organic mixes are quite good and consistently free of pathogens, and good with nutrients, but occasionally even these fail. Home made mixes, such as the one I make, fail more regularly. Here are some of the problems I have seen frequently in my home made mix, and occasionally in commercial mixes.
Damping-off: Damping-off is a disease most commonly seen in young seedling but may rarely effect older seedlings. It is caused by species of fungi that commonly live in the upper layers of soil and when things are not right these pathogens jump at the opportunity to infect germinating seeds and seedlings. The two most common species that cause damping off are in the genera Pythium and Rhizoctonia.
There are two types of damping off. The first is one growers often misinterpret because it is pre-emergence damping-off, which rots the sprouting seed before it breaks through the soil. Growers often blame the seed companies for poor seed. The fungus attacks any part of the germinating seed especially the tiny growing tip. Post-emergence damping-off begins as a lesion on the root which extends up the stem to and/or above the soil line. The young stem is constricted by the attack and becomes soft, and the plant falls over and dies.
Damping off cannot be cured but it can be prevented by starting seeds in better conditions (or the "sterile" media). First make sure you are using seeds of the highest quality. Old, mistreated, and weak seeds are more susceptible to damping-off. Anything that slows germination increases the risk of infection. Excessive watering, poor drainage and less then optimum temperatures should be avoided. Allow the surface of the container to dry a bit before watering.
It is possible to "sterilize" your media by baking the mix in the oven at 350 F for about 45 minutes. The mix should reach 1600 and should stay at that temperature for 30 minutes. Do not allow it to go higher or stay hot longer because overheating kills the beneficial microorganisms and may releases toxic materials
Cold Soil/Wet Soil: In addition to damping off, cold soil can cause other problems. Growing seedlings on window sills is often a problem because of cold night time temperatures. The roots of plants do not function when cold and plants frequently display symptoms of malnutrition even thought the media may have plenty in it. Purple undersides of leaves, stunted growth, pale weak seedlings are often the results of cold feet or wet feet. Trying to grow a tiny seedling in a large container may have the same effect because the plant is just not big enough to use the water and over watering may be a problem the plant cannot get out of.
Salt: Some composts are high in soluble salts. Even if the salts are nutrient salts such as nitrates, high salts will cause water absorption problems and may prevent seeds from germinating. Salty composts are not a problem in field use because they become diluted with the soil, but in a seedling media it is a real problem. Compost used for media should be the best you can get and should not have salts -measured as conductivity on a compost analysis- higher than 1mmhos.
Carbon:Nitrogen: The C:N ratio is critical for compost used in potting mixes. A high C:N ratio will result in nitrogen lock up, which is a case where all the nitrogen in the media, and any you add with fertilizers, is being grabbed by the bacteria feeding on the carbonaceous material. It is a sign that the compost was made from an improper mix of feedstock, or perhaps is just not finished yet. Compost used to make media should have a C:N ratio of 15:1 to 18:1.
Ammonia: As nitrogen is released from decomposing proteins in a compost pile it passes through a phase where it is an ammonium ion. Unfinished compost will have ammonium ions that may revert to ammonia and kill roots. Ammonia nitrogen in a compost used for a potting soil should be less than 0.1%. Problems from high ammonia can be seen as very weak, dying seedlings, and when you pull them up you see that the roots are brown instead of a nice healthy white.
My recommendation is to get an analysis of any compost you plan to use to build your own seedling mix. The University of Maine Soil Testing Laboratory does compost testing. Just be sure if you send a sample to ask for the compost analysis. If you are buying a commercial compost based mix you may want to speak to other growers and see how that brand has worked for them.
DAMPING-OFF IN THE FIELD
Above I discussed damping-off of seedlings. Last year I received calls about peas dying just after or just before germinating and I thought I better say that damping off can occur in the field too. This time of year the problem is with peas.
The disease is caused by several different species of Pythium, which is a common soil inhabitant that persists in soil in root debris as spores. The species have a wide host range of crops and weeds and so crop rotation will do little to avoid the problem.
During or just after germination the pea seedling begins to show symptoms. The symptoms may be as simple as yellowing and stunting because sometimes only the root tips are infected and this root pruning interrupts growth. Sometimes a soft rot of the stem kills the plant. Sometimes you just don't see any pea germinate.
High soil moisture and warm soil temperatures (warmer than optimum for pea growth, i.e., 65-75) favors Pythium. You can't control the weather but you can choose when you plant your peas. If the soil is very wet and warm weather is forecast it may make sense to delay planting a few days for the soil to dry a bit.
There are resistant varieties. The resistant gene is tied to some visual characteristics of the seed. Wrinkled seeds are more severely affected than round seeds. Also, some biological seed treatments such as Rootshield may help.
POTATO PLANTING TIME: DON'T PLANT A PROBLEM
Potato seed tubers are often the source of infection for your crop and inspection before planting is well worth the time. Some problem seed pieces are not going to spread a disease and can be planted. Others should never be planted. Here are some common issues:
|Late blight on tubers. Photo by Eric Sideman.
Late Blight: Of course this is the big one. Look at the picture on the web version if you don't know what this looks like. If you are not sure, check with an expert. Besides taking down your potato crop, this is the most likely source of a community or state wide problem this year. Do not plant any potatoes suspected of being infected with late blight.
Fusarium Dry Rot: This is probably the greatest cause of loss in storage. It is also seen on seed pieces, and can result to seed piece decay after planting and result in uneven stands. A slimy rot ofen develops when Fusarium dry rotted potato seed is planted. This is a secondary infection by bacteria, which take over. Do not plant seed pieces with Fusarium dry rot.
Ring Rot: This is one of the worst diseases you can get on your farm because once you get it it is very hard to get the farm clean again, and it spreads very easily by the bacteria clinging to boots, crates, and equipment. Check your seed carefully and discard the whole load if any ring rot is found. In the tuber you will see the disease as a break down of the ring of vascular tissue when you cut the potato. Squeezing the tuber will expel creamy, odorless ooze of bacteria. Planting these tubers will introduce the bacteria to your soil.
Scab: Lesions on the tuber are usually circular and seldom larger than a half inch, but in very bad infections they coalesce. They may be a cork like layer or pitted. The layer under the lesion is straw colored. Planting these tubers will introduce the bacteria to your soil.
Black Scurf: If you have little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, then you have black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani. The black specks are one of the ways the fungus reproduces. They are called sclerotia, which are tight, dry masses of fungal tissue (mycelium) in a resting phase. In the spring the sclerotia germinate and infection of the new potatoes begins. Most commonly, infection of potatoes is from planting potato seed pieces with sclerotia on them. Crop rotation is not very effective because sclerotia can survive for many years without a host crop. So, avoid ever planting seed with the disease.
Hollow Heart: Just as the name implies, the center of the potato is hollow. It appears as splitting with the tuber and the inner walls may be white, tan or even may be rarely infected with a secondary disease. Hollow heart is not caused by a pathogen but rather by rapid tuber enlargement especially after a period of moisture stress. Potato seed with hollow heart will not spread the disease.
Knobby potatoes: Potatoes with knobs are usually the result of high field temperature and drought or other conditions that cause irregular rates of tuber development. Planting knobby potato seed will not spread the problem.
This is the first Pest Report for the 2010 growing season. The Pest Report is sent out every week or two during the heart of the season and highlights problems happening then or likely to show up soon. I hear about problems from growers all around the region so please help out and let me know if something big or unusual is happening so I can share the information.
I write much of the Pest Report, and much of the writing is reprinted from newsletters by crop advisors around the region. The ones I use the most are from the University of Vermont (Vern Grubinger), University of Massachusetts (Ruth Hazzard), and the University of New Hampshire (Becky Sideman). As you can guess, using material from there often gives us here in Maine a bit of time to prepare because many pests move into Maine from the south and west during the season, i.e., do not spend the winter here. Also, this year I will be picking out some pieces from previous Pest Reports because usually the warning is the same year after year.
The Pest Report pieces include a description of the pest, the biology of the pest, a description of the damage, and some suggested management practices allowed under organic standards.
This Pest Report is being sent to everyone on my list in 2009. If you were a MOFGA certified grower in 2009 and did not renew in 2010 you will NOT automatically receive the Pest Report. You will have to write to me and request to be added to the list of non-certified growers receiving the report.
PEA WEEVIL Bruchus pisorum: You may not even know that pea weevil is a problem for you. You may be wondering why germination of your seed is low but never make the connection. Of course, there are many other reasons why pea seed germination is low, so don't make assumptions. The problem is not common or big here in the Northeast.
Adult pea weevils are short, chunky beetles with brown, white, black and gray flecks. They are not true weevils and so do not have the typical snout. Adults hibernate though the later part of the summer, fall, and winter under bark, crevices of fence posts, sides of buildings, crop debris, etc. In the late spring when the peas are flowering the awake adults are flying and smelling the flowers. After feeding on pollen for a while the females lay eggs on the newly forming pea pods. They lay eggs, which look like little cigars singly, but there may be more than one egg on each pod. When the eggs hatch in 2-4 weeks, the white grubs with a small brown heads borrow through the pod into the young peas. They grow inside the pea for about 5-6 weeks consuming the contents. Then they chew an escape hole and pupate. In as little as 1-3 weeks after pupation the new adult may come out using that escape hole and fly off to hibernate. But many adults just stay in the pea and hang out until things seem good, or they are disturbed by jostling or planting or something. There is no tolerance in the market for peas with grubs in them, and people selling and buying seed are not happy when a good portion of them are truly shells of what they should be.
There are no silver bullets for organic pea growers. Management practices are aimed at reducing the population. Conventional growers will spray when the flowers begin to wilt but before pods are sizing. But first they scout the field to see if the pea weevil is a problem. Scouting is done with a sweep net around the edge of the crop starting when flowering begins. The critter is only active when it is warmer than about 65 during the day. Sprays have to catch the adult because once the eggs are laid and larvae bore into the pod there is no way to catch them. I have been unable to find studies of efficacy of organic insecticides for pea weevil, yet.
Cultural practices are the most important means of reducing numbers for organic growers. Harvest peas when they are ready and do not leave crops hanging around after harvesting season, which would allow adults to leave the peas and move to hibernating sites. Clean up spilled peas and destroy crop debris right after harvest for the same reason. The important thing is that it does not seem to be a big problem here in the Northeast and your most important practice is to not plant infested seed.
SEEDCORN MAGGOTS Hylemya platura [Reprinted and modified a bit from New Hampshire Vegetable, Berry and Tree Fruit Newsletter by Becky Sideman]. Last spring, I heard a couple of reports of seedcorn maggots causing damage for vegetable growers. Now is the time to be aware of the problem. Seedcorn maggot larvae feed on seeds and young seedlings of many crops (corn, beans, beets, peas, cole crops, etc.). The first symptoms are usually poor germination (or failure of seedlings to emerge). Symptoms can be difficult to distinguish from other problems, like damping off due to Pythium or other soilborne fungi, or wireworm feeding. If seedcorn maggots are the culprit, maggots can usually be found in the soil around and inside seedlings and seeds. The seedcorn maggot is yellow-white, 1/4 inch long, legless, with a wedge-shaped head. The adults look like small houseflies. Seedcorn maggots overwinter in the soil as pupae. In early spring, the adults emerge and lay eggs, which hatch within 2-4 days at soil temperatures of 50F. In Minnesota, research has shown that peak emergence of the first three generations occur when 200, 600 and 1000 degree days have accumulated. Degree days are calculated on a daily basis by using the formula: (Max temp – Min temp)/2 – 39F. You can also refer to a handy calculator at http://www.weather.com/outlook/agriculture/growing-degree-days. This calculator tells me that we already reached 200 DD using a base temperature of 40F by April 12, which is much earlier than normal. The first generation usually causes the most damage. Will seedcorn maggots be a problem this year? It depends. The adults prefer to lay eggs in wet soil that is rich in organic matter. Crop seeds that germinate slowly are more vulnerable to attack. The adults are likely to be active ahead of schedule this year, and crops that are planted in wet soil when the soil is too cool for them to germinate quickly may be especially susceptible to damage.
By the time you see damage, it is too late to control the problem using either cultural or chemical methods. Prevention is the key.
- Avoid seeding fields (especially wet fields) too early. Seeds germinate more quickly and are less vulnerable in warmer soils.
- Disk and incorporate organic matter (such as a cover crop) at least 4 weeks before seeding to give it time to break down and make it less attractive to the flies
- Avoid applying manure in late fall or early spring to heavy soils that you might want to plant early. Lighter, well-drained, sandy soils are less likely to have problems (because they warm up faster than others).
- Rowcovers can help – but only if the maggot flies are coming from elsewhere. Damage can occur if the flies have overwintered in the soil underneath the rowcovers.
- If you need to replant, wait at least 5 days if maggots that you find are a quarter inch long; if they are smaller than that, wait at least 10 days to make sure they have pupated and will not damage the new seeds.
LATE BLIGHT: I bet you are all tired of hearing about late blight and mostly hope that there is not a lot of talk about it this year. I want to make sure that everyone understands that late blight does not overwinter in New England EXCEPT in potato tubers. The very important message to get out is to make sure your potato seed is not diseased, and to look for any volunteer sprouts from potatoes left in the field, garden or piles. If diseased potatoes sprout they will then start spreading spores. Late blight does not live in tomato debris, or tomato seed. The only way to get it to New England on tomatoes is to carry the tomatoes here from the south already infected, as was not so kindly done for us last year. Do not support any store buying tomatoes that were grown for any time down south.