CROP ROTATION: Most of the disease, insect and weed problems you will have this season have already occurred and now in addition to maintaining your control of these you need to start thinking about next season. For many pests the severity of the problem next year will be the result of what you do this year. For insects and diseases the worst practice you can do is have a dependable food source available for them year after year. The problem will likely get worse and worse. The most effective practice to avoid this is crop rotation. That is why the National Organic Program Rule requires crop rotation where it is appropriate. Now is the time to decide where crop rotation will work to disrupt the dependable food source your insects and disease pathogens hope to find.
Effectiveness of crop rotation depends on the life history and biology of the particular pest. The three characteristics that play the biggest role are:
- Dispersal ability- How well and far can the pest move? If the pest can only move short distances then by rotating your crops to a new field you can leave them behind unable to reach food before they starve. On the other hand, if the pest typically moves long distances then if you put your host crops here or there it will not make a bit of difference. For example, the potato leaf hopper comes here all the way from the Gulf of Mexico region and so chances are that which field you put you beans or potatoes in will not make a difference. In contrast, the Colorado potato beetle hibernates during the winter and essential can only walk to potatoes when it wakes up in the spring. You do not have to move potatoes too far from last year's field to significantly reduce the numbers that find the new planting.
- Host Specificity- How many different kinds of plants does the pest feed on? If the pest is very specific in what it eats it is easier to choose an alternative crop to plant where the pest is overwintering. On the other hand, if the pest feeds on many crops (or weeds) then it is difficult to avoid a food source for it and it will probably be waiting for you no matter where you move your crop or how long you wait to plant it again. For example, the tarnished plant bug, which is a major pest on lettuce (browning of the midrib), strawberries (catfacing), eggplant (feeds on tiny buds and they drop) and broccoli (brown beads in head), also feeds on about 300 weeds and so really does not depend on your crops to survive. In contrast, the species that causes Septoria leaf spot on tomato can only survive on plants in the tomato family (tomato, eggplant, potato, petunia,
black nightshade, etc) so it is not that hard to plan a successful crop rotation to leave it without a host to feed on.
- Persistance- How long can the pest survive without a host? This is a critical question because some diseases can persist in some sort of resting spore for very long periods of time waiting for a host to appear again. Most insects need food every season or they starve and many diseases can only survive a year or two without a host. For example, the pathogen that causes late blight of potato and tomato can only survive on living tissue and so in New England it really only makes it from season to season on potato tubers. Proper handling of culls is key to managing this disease. In contrast, the pathogen that causes white mold of beans, carrots, tomato, lettuce, etc. can form resting bodies called sclerotia that are able to just sit in the soil for many years without any host.
So, now is the time to look around the farm and see what you have for pests and learn which ones can be managed with crop rotation and then make plans. Crop rotation does not work for pest management in gardens because almost any pest can move from one side of a garden to another, especially when the gardener pushes the tiller back and forth. That does not mean that gardeners should not rotate. Crop rotation, in addition to a tool for pest management, is very important for managing nutrients in the soil and for controlling weeds, and this is true for both farmers and gardeners.
Rotations used to control weeds include rotations with other crops as well as rotation with fallow ground or ground put into cover crops instead of cash crops. Fallow periods allow the grower to periodically till the ground which kills growing weeds and stimulates weed seeds to germinate that later can be killed by the next tilling. This practice is of course bad for the soil structure, but in situations may be the best approach for cleaning up a field before going back to good soil building practices. In situations where weeds are totally out of control the fallow period may be long and include lots of soil-damaging tillage. But, in later, once the weeds are under control, the fallow period can be shortened and most of the rotation can be with cover crops instead of bare ground and tillage.
Basic rotation plans to control weeds, in addition to rotating with fallow periods, include:
- Rotating vegetable crops that are hard to cultivate and keep weed clean with those that are easy
- Growing short season crops that allow half a season for cover crops
- Alternate early season crops with late season crops to allow attacking spring weeds one year and fall weeds the next
- Take land out of production and grow a series of short season cover crops such as oats, then buckwheat, then oats for the fall
Rotations used to manage soil fertility include planting fall cover crops to avoid loss of the many nutrients left after crop harvest, rotations of heavy feeding crops with light feeders, rotating crops that tap shallow soil with those that tap deep soil and rotating nitrogen fixing green manures with cash crops. Using crop rotation with nitrogen fixing legume green manures is a prime way that farms can reduce their environmental impact. Not only are nitrogen rich fertilizers environmentally costly to produce they also may indirectly lead to excessive phosphorus in the soil. Typically, farmers and gardeners determine how much soil amendment to add based on the nitrogen analysis of the material and many materials typically used to add nitrogen (ex. Manures, organic waste, etc) also add phosphorus. After years of this practice it may result in excessive phosphorus in the soil that may end up as pollution in surface water. Using nitrogen fixing crops in a rotation adds nitrogen to the soil with no other nutrients.
Whether you are a farmer or gardener it is time to plan your rotation now. For more information on using green manures in crop rotations, including fall cover crops, see MOFGA Fact Sheet #10 Using Green Manures.
PUMPKIN AND WINTER SQUASH HARVEST AND STORAGE (reprinted from Umass Veg. Notes): Although there are many fields with immature fruit, pumpkins in some fields are orange. Sugar pumpkins, especially, are ready early. Butternut in some fields is showing the dull, dry skin that characterizes mature fruit. If the current warm sunny days continue [not warm here in Maine anymore, is it?], more and more pumpkin fruit will color up in the next several weeks. Fruit sitting in the field faces a daunting list of diseases and insects - not to mention possible passing hurricanes -- that could threaten fruit quality. Early harvest and careful storage is 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 Phytophthroa blight.
Pumpkins may need to be held for several weeks before they can be marketed. 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 are not 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, Fusairum, 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 in the seventies to low eighties. 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.
Winter squash is also maturing in some fields. Fruit that are free from disease and haven't been subject to much chilling (below 50°F ) should be selected for long-term storage. Fruit from fields where Phythophthora is present are not the best choice for storage. 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. With so many late-planted field this year, early pumpkins are likely to be in demand. --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; and Liz Maynard, Purdue University
ALTERNARIA DISEASES OF BRASSICAS (modified from a report in Umass Vegetable Notes by Beth Dicklow and Rob Wick): Three species of Alternaria cause serious damage to brassicas: Alternaria brassicicola, A. brassicae, and A. raphani. Alternaria brassicicola and A. brassicae infect broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, kohlrabi, kale, rutabaga, and turnip. A. raphani is most often found on radish, but can infect other brassica crops. The most common symptom of Alternaria diseases is yellow, dark brown to black circular leaf spots with target like, concentric rings. Lesion centers may fall out, giving the leaf spots a shot-hole appearance. Individual spots coalesce into large necrotic areas and leaf drop can occur. Lesions can occur on petioles, stems, flowers, flower pedicels, and seed pods. Pod infection causes distortion, premature shattering, and shriveled, diseased seed that germinates poorly.
Alternaria species are simple parasites that survive saprophytically outside the host. Diseased crop debris is the primary site of survival from year to year. Resting spores (chlamydospores, microsclerotia) have been reported. The disease is favored by warm temperatures (60-78° F) and at least 12 hours of relative humidity of 90 % or more. The fungi sporulate profusely and are spread throughout fields by wind, splashing water, equipment, and workers. The main means of introduction into new areas is on infested seed.
- Buy seed certified as disease-free or treat seed with hot water. [for details on hot water seed treatment, see The Resource Guide for Organic Insect and Disease Management, page 12]
- Practice long rotations with non-brassica crops.
- Incorporate diseased plant debris into the soil.
- Eliminate cull piles.
- Control brassica weeds.
- Avoid overhead irrigation during head development.
- Keep seedbeds disease-free to prevent the spread of disease and locate seedbeds so as to avoid wind-borne inoculum.
- Control of Alternaria leaf spot on cabbage heads in the field is necessary for long-term storage.
Copper compounds are labeled for Alternaria in brassica crops but recent studies have shown poor results.
Powdery Mildew: Meg McGrath has just finished up an article reporting her recent research that looked at organic methods for managing powdery mildew of cucurbits. She has kindly allowed me to reprint it here. This is very timely because I am seeing PM moving quickly into fields, especially pumpkins. Fields in early stages of disease development may still be worth treating. Thank you, Meg, for this and all your other work.
Guidelines For Managing Cucurbit Powdery Mildew Organically
Margaret Tuttle McGrath, Department of Plant Pathology, Cornell University, Long Island Horticultural Research and Extension Center; 3059 Sound Avenue, Riverhead, NY 11901; firstname.lastname@example.org; vegetablemdonline.ppath.cornell.edu
Powdery mildew is the most common disease of cucurbit crops occurring every year throughout the US. The characteristic white, powdery fungal growth is readily recognizable on leaves and vines. This growth is mostly spores that are easily dispersed by wind. Symptoms can be difficult to see on watermelon, however, as spores are produced less abundantly than on other cucurbits. Uncontrolled powdery mildew indirectly affects yield because infected leaves usually wither and die. Premature loss of leaves can result in reduced market quality because fruit become sunburnt, have poor color, or have low sugar content due to ripening prematurely or incompletely. Fruit with low sugars have poor flavor and poor storability. Handles on pumpkin fruit may be shriveled or rotten in addition to fruit being paler orange. Size and/or number of fruit can be reduced in summer squash and in other crops when powdery mildew is severe. Severe disease can also lead to imperfections on fruit rind such as speckling and oedema. In addition, powdery mildew infection predisposes plants to other diseases, in particular, gummy stem blight (aka black rot).
Powdery mildew can be managed with resistant varieties and regular foliar applications of disease control products and fungicides*. It is not possible to escape infection because the pathogen produces many wind-dispersed spores, cucurbit crops are grown widely, and conditions often are favorable for this disease. The powdery mildew fungus tolerates a wide range of temperatures below about 100 F and it does not need a period of free moisture on leaves to infect, in contrast with other foliar fungal pathogens. Rain is actually unfavorable. The fungus causing powdery mildew fortunately is sensitive to many types of chemicals that are approved for organic production. These include oil (mineral and botanical types), sulfur, copper, potassium bicarbonate, and biofungicides (Table 1). Efficacy and cost vary widely. Few products are labeled for other diseases. For effective control, applications need to be started very early in disease development and repeated every 7 to 10 days (14 days with resistant varieties). Established powdery mildew cannot be controlled, not even with systemic conventional fungicides. Routine scouting is needed to ensure applications are started very early in powdery mildew development. Plants are susceptible to powdery mildew when in their reproductive phase and at any age when grown under greenhouse conditions. Sometimes symptoms begin to develop on field-grown plants before they begin producing fruit, especially when severely stressed due to delayed transplanting or surrounded by tall weeds; removing these stresses can halt powdery mildew development thereby avoiding the need to start applications early. Inspect plants weekly. When first fruit start to enlarge is an especially important time. The scouting protocol entails weekly examining both leaf surfaces of 5 old, crown leaves in at least 10 locations through out a field. Symptoms develop first on older leaves, often on the underside. It is time to start applications when powdery mildew is found at a very low level on at least 1 of the 50 leaves. Once symptoms are easily seen without hunting, potential to effectively manage powdery mildew with rescue treatments is greatly diminished.
The pathogen develops best on the lower surface (underside) of leaves, thus a successful management program necessitates controlling the pathogen on the lower as well as the upper surface to avoid premature death of leaves.
Unfortunately there are no products with systemic activity approved for organic production and it is difficult to directly deliver fungicide to the lower leaf surface, even with new nozzle types and air assist sprayers. Foliar applications of sulfur have been more effective than most other organic products for powdery mildew on lower surfaces when compared in fungicide efficacy experiments, apparently because when deposited on the upper leaf surface, sulfur can volatilize and be redistributed to the lower surface. Sulfur is also less expensive than other materials. Like copper, sulfur is an element and thus cannot be degraded and removed from the environment as can materials such as oils. Sulfur is a micronutrient for plants. Note that sulfur can be phytotoxic on melons, especially if applied when temperatures are hot.
All products listed in Table 1, except MilStop, have been evaluated in replicated experiments conducted since 1997 in Riverhead, NY, and found to be effective for powdery mildew. All are considered protectants since they do not move into plant tissue. Product efficacy for providing full-season control ranged from poor to at least as good as the popular conventional protectant fungicide chlorothalonil formulated as Bravo. The most effective products were Microthiol Disperss and Eco E-Rase. GC-3 organic fungicide, Organocide, JMS Stylet-oil (organic formulation), and Champion were also highly effective. No experiment included all products thus they cannot be ranked. Tables of these experiment results will be posted on line at http://vegetablemdonline.ppath.cornell.edu/.
In summary, to ensure good yield of high quality fruit of cucurbit crops, manage powdery mildew by selecting varieties with resistance, examining foliage weekly to detect when this disease begins to develop, and applying control products to foliage beginning very early in disease development.
Please Note: Organic growers should ask their certifier about product acceptability for their operation before purchasing. The specific directions on fungicide labels must be adhered to -- they supersede these recommendations if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended.
* note that in the US products for which the manufacturer claims disease control must be registered as fungicides with EPA unless the ingredients are 'generally recognized as safe' (GRAS) by EPA.
Table 1. Biocompatible products evaluated for managing powdery mildew, active ingredient, whether exempt from tolerance and EPA registration as a fungicide, labeled diseases and insect pests, and company. Note that a few are not yet OMRI listed. A few products are not labeled for use for powdery mildew on cucurbits (target pest must be specified on the label to be used in NY).
1. Bugitol. 0.42% capsaicin and related capsaicinoids, 3.7% allyl isothiocyanate. Kills and repels numerous insects, no diseases on label. Champon Millennium Chemicals. $28.56 at 96 fl oz/A. Not OMRI approved yet. EPA Reg No. 61966-4.
2. Eco E-rase. 97.50% jojoba oil. Controls powdery mildew and white fly. Labeled presently for use on grape and ornamental crops. IJO Products. $16.25 at 0.5% applied at 50 gpa. OMRI listed. Exempt from tolerance. EPA Reg No. 68186-1.
3. GC-3 Organic fungicide. 30% cottonseed oil, 30% corn oil, 23% garlic extract. Controls powdery mildew. JH Biotech, Inc. $23.75 at 1% applied at 50 gpa. OMRI listed. Exempt from EPA registration.
4. Organocide. Active ingredient=5% sesame oil; inerts = 92% fish oil + 3% emulsifiers. Labeled for several diseases and insects. Organic Laboratories, Inc. $47.50 at 2 oz/gal. OMRI listed. Exempt from EPA registration.
5. Sporan. 17.6% rosemary oil; Other ingredient = 82.4% wintergreen oil. Labeled for several fungal diseases. EcoSmart Technologies. $29.25 at 1.5 qt/A. OMRI listed. Exempt from EPA registration.
6. Trilogy. 70% clarified hydrophopic extract of neem oil. Labeled for several diseases and insects. OMRI listed. Certis USA L.L.C. $12.00 at 1% applied at 50 gpa. EPA Reg No. 70051-2.
7. Milsana. 5% ethanolic extract of Reynoutria sachalinensis (giant knotweed). Boosts plants' natural defense mechanisms; certain fungal and bacterial diseases. Label recently expanded from just ornamental greenhouse crops to include use in field on food crops. KHH BioSci, Inc. $8.75 at 2 qt/100 gal applied at 50 gpa. EPA Reg No. 72179-2.
8. Prev-Am. 0.99% sodium tetraborohydrate decahydrate. Labeled for several diseases and insect pests in addition to powdery and downy mildew in cucurbits. ORO Agri, Inc. $11-27.50 at 0.4-1% applied at 50 gpa. EPA Reg No. 72662-3.
9. AgriLife. 5% citric acid. Natural plant immune booster. Broadly labeled for fungi and insects. Biological Solutions, LLC. $30-60 at 0.5-1% applied at 50 gpa. Exempt from EPA registration.
10. JMS Stylet-oil, organic formulation (note that there is another formulation). 97.1% paraffinic oil. JMS Flower Farms, Inc. $7.43 at 5 qt/100 gal applied at 50 gpa. OMRI listed formulation. EPA Reg No. 65564-1.
11. Serenade. Bacillus subtilis. Labeled for several diseases. OMRI listed. AgraQuest. EPA Reg No.69592-11.
12. Sonata. Bacillus pumilus. Labeled for several diseases. OMRI listed. AgraQuest. EPA Reg No. 69592-13.
13. OxiDate. 27% hydrogen dioxide. Labeled for several diseases. OMRI listed. BioSafe Systems. $21.58 at 128 fl oz/100 gal. EPA Reg No. 70299-2.
14. Armicarb. 85% potassium bicarbonate. Labeled for powdery mildew and other diseases. Helena Chemical Company. $12.69-16.92 at 1.5-2 lb/A. EPA Reg No.5905-541.
15. Kaligreen. 82% potassium bicarbonate. Labeled for powdery mildew. $21.41 at 4 lb/A. OMRI listed. AgBio, Inc. EPA Reg No. 70231-1.
16. Milstop. 85% potassium bicarbonate. Labeled for several diseases. BioWorks, Inc. EPA Reg No. 70870-1-68539.
17. Nutrol. potassium dihydrogen phosphate (0-50-32). Labeled for powdery mildew. $11.36-17.04 at 8-12 lb/A. Not OMRI listed. LidoChem, Inc. EPA Reg No. 70644-1.
18. Champion. 77% copper hydroxide. Labeled for several diseases. OMRI listed. NuFarm Americas Inc. $5.70/A at 2 lb/A. EPA Reg No. 55146-1.
19. Microthiol Disperss. 80% sulfur. Labeled for powdery mildew. Will be OMRI listed soon; other sulfur products OMRI listed. Cerexagri. $2.64/A at 4 lb/A. EPA Reg No. 4581-373.
Plectosporium Blight [on Zucchini] (modified from a report by T. Jude Boucher, University of Connecticut, Cooperative Extension System)
Plectosporium blight, caused by the fungus Plectosporium tabacinum (formerly known as Microdochium tabacinum), is a new destructive disease of cucurbits in New England. This disease was found in Tennessee in 1988 and has since spread rapidly throughout the eastern United States. It occurred on a single farm in Massachusetts in 2000 and on at least a dozen farms in Connecticut and Massachusetts in 2003. In the fall of 2004, after two seasons of rainy weather, it was present in every field Jude visited from Long Island Sound to Burlington, Vermont. I am now seeing it this season in Maine on zucchini.
Plectosporium blight is known to cause damage to a wide variety of cucurbit crops in Europe and Asia, but the strain present in the U.S. seems to primarily damage pumpkins, summer squash, zucchini and a few varieties of gourds. In wet years, which favor disease development and spread, crop losses in no-spray and low-spray fields can range from 50 to100%.
Fortunately, this disease is easily recognized but is difficult for organic growers to manage. If you spot it, be prepared to implement good sanitation and develop a effective crop rotation of your cucurbits to clean fields next season.
Description and Management: The clearest symptom to look for on vines and petioles are white lesions that tend to be diamond to lens-shaped; and on fruit and leaves the lesions are usually round and white. [see http://www.umassvegetable.org/soil_crop_pest_mgt/disease_mgt/zucchini_plecto sporium_fruit.html].
Plectosporium blight is favored by cool, rainy weather. The fungus can overwinter on crop residue and can persist in the soil for several years. Plectosporium has not been reported to be seed-borne. Tiny, one or two-celled, sickle-shaped spores are formed in lesions on vines, stems, fruit, leaves and leaf petioles. Spores are dispersed by wind over long distances. Lesions are small (<1/4 inch) and white. The lesions increase in number and coalesce until most of the vines and leaf petioles turn white and the foliage dies. Severely infected pumpkin vines become brittle and will shatter if stepped on . Early in the infection cycle, foliage tends to collapse in a circular pattern before damage becomes more universal throughout the field. These circular patterns can be easily detected when viewing an infected field from a distance. Numerous fruit lesions produce a white russeting on the surface and stems that render the fruit unmarketable. Fruit lesions also allow for entry of soft rot pathogens that hasten the destruction of the crop.
Disease management recommendations include:
∑ a three-year crop rotation
∑ planting in sites with good air circulation to encourage rapid drying of the foliage
∑ switching to trickle irrigation
∑ scouting fields to confirm the presence of Plectosporium, applying fungicides, and plowing under crop residue after harvest
∑ Although there are some fungicides for conventional growers the fungicides available to organic growers are not thought to offer adequate control.
An evaluation of resistance to the disease by different varieties can be found at the web site noted above.
Pepper Maggot Found in New Hampshire (From Alan Eaton, UNH Cooperative Extension)
On July 28th, a Rockingham County pepper grower brought in fruit with unusual deep dimples. I suspected pepper maggot, and set up traps Saturday. By Sunday we had two adults. This is the first time we've found these in New Hampshire. The adults lay eggs in the fruit, and the eggs hatch into maggots that feed especially in the seed head, and it becomes tunneled and rotten. The injury is new to most of us, and you can imagine the reaction of your customers if the fruit they bought has maggots wriggling inside.
If you have fruit with deep dimpled spots here and there, you might have it, too. Hillsborough, Rockingham and possibly southern Strafford Counties are the most likely to be infested. There are controls (see the New England Vegetable Management Guide), but you can't kill the eggs already laid inside the fruit. Here's a link to Jude Boucher's excellent article on pepper maggot and its management, at the UConn Extension IPM page:
TARNISHED PLANT BUGS (modified from an article by Ruth Hazzard in Mass. Veg. Notes) Tarnished plant bug adults and nymphs are being found in several vegetable crops, and in some fields they are causing signifcant damage. We have had calls about damage to the ribs of Romaine lettuce. Most likely it is the second generation of adults that are feeding now. There are several species of tarnished plant bugs in the US, but the most common in central and eastern US is Lygus lineolaris. Adults are about 6 mm long (1/4 inch), brown or tan or greenish with darker markings on their wings and back. Nymphs are bright green and progress through 5 molts (instars) from first hatch to the adult stage. The nymphs can be mistaken for aphids, but move much faster when disturbed. Overwintered adults lay eggs in spring, depositing eggs in stems and leaf ribs in host plants. These adults and nymphs attack strawberry flowers in May. A new generation of adults (which is what we are seeing now) will produce another brood in the late summer, for a total of 2 or possibly 3 generations per year.
Feeding: Adults and nymphs have piercing sucking mouthparts (stylets) which are used to penetrate plant tissues and suck up cellular contents. TPB select succulent, nutritious tissues such as new growth or newly forming fruits (just after blossoming). While feeding, the bugs secrete a toxic substance from their salivary glands, which kills cells surrounding the feeding site. Usually the first signs of damage are small brown spots on young leaves. As the tissue grows, healthy tissue expands while dead tissue does not, which results in holes and distorted, malformed leaves, buds or fruit. Terminal shoots and flowers may be killed.
Damage: Over half of the cultivated crops in the US are listed as hosts. In strawberry, this distorted growth of fruits is known as cat-facing. In lettuce, leaf stems and ribs are injured, causing localized discolored scars and scabs. In celery, feeding on tender stalks produced large, brown colored wilted spots and blacking of joints, know as "blackjoint'. In beans, feeding on flowers causes them to drop, and feeding on seeds in young pods causes pitting and blemishing of pods. In tomatoes, eggplants and peppers, feeding may occur on flowers and stems, causing flower drop, a very common cause for little or late fruit even though the plants are robust. Fruits may also be attacked leading to indentations, bumps, or yellowing of the flesh where the fruit is "stung" by the piercing mouthparts of nymphs or adults. These could be confused with stink bug damage, but they do not have the white pithy areas beneath the skin that is typical of stick bug damage. It is not common to see this damage, but if the damage occurs it may help to determine the cause. In pepper and in basil, feeding in emerging leaves causes distortion and browning of leaves. In apples, adults feed on fruit buds and cause fruit dimpling and scabbing, or dropping off (abscission) of the buds.
Weeds and field crops are also host plants: Tarnished plant bugs attack a large variety of weeds, flowers, forage crops, and orchard crops. Weed hosts include wild carrots and other umbelliferous crops, redroot pigweed (and other amaranths), lambsquarters, mustards, shepardspurse, rocket, goldenrod, and mullein. Alfalfa is a favored host, and harvesting alfalfa often stimulates major lygus migrations. Other legume hosts include vetch, lupine, and fava beans. Where weedy areas or field crops surround vegetable fields, continuous re-infestation of vegetables is possible.
Management: Vegetation management on the whole farm is very important for these highly mobile pests. Focus on removing sources of infestation outside the crop. Disk or rototill weeds along field borders to reduce weed hosts, or keep them mowed all season. Similarly, keep grassy areas on the farm mowed short, to reduce their attractiveness as hosts. However, disturbing non-crop areas by mowing can encourage movement of TPB into your crop, so it should be avoided at critical periods when the crop is vulnerable. There are natural enemies of TPB, including a parasitic wasp, which was released for control of TPB in alfalfa (Peristenus digoneutis). This was released in New Jersey and has spread throughout the Northeast, and can cause up to 50% mortality. However, it currently does not reduce the numbers sufficiently to prevent damage in key crops. Common predators, such as ladybeetles, spined soldier bugs and insidious flower bugs also prey on nymphs. White sticky traps placed above the canopy are used in strawberry and can be used in vegetables to indicate when adults are present. Economic thresholds have been determined for crops where TPB is a key pest, but not in most vegetable crops. It is difficult to sample tarnished plant bugs directly on plants, because they are very mobile and like to hide. In strawberry, nymphs are shaken off the flower clusters onto a flat surface and sprays applied if 4 out of 30 clusters have nymphs. If damage is unacceptably high, use insecticide applications. Labeled products for TPB on lettuce are listed in the 2006-2007 New England Vegetable Management Guide and include Pyganic for organic growers. Avoid applications during bloom periods. Insecticide labels often list "lygus bug" instead of specifcally "tarnished plant bug". --Ruth Hazzard
FLEA BEETLES: PLANT LATE BRASSICAS FAR FROM SPRING CROPS. (from Mass. Veg. Notes) Mid July is often a time of year when adult FB numbers decline, because a large part of the population is underground, in larval and pupal stages. After larvae feed on roots, they pupate in the soil, then emerge again "into the light" as adults-ready to feed on foliage. The time when you will first see these new adults depends on when eggs were first laid on spring Brassica crops, and on soil temperatures since then. Dissections of flea beetles collected from the field in the Connecticut Valley in April and May detected eggs present in early May this year; hence new adults are likely to be emerging now. In fields where Brassica crops are always present, because succession crops are planted close together, it may appear that flea beetles never go away all summer. In fact, they are likely to increase dramatically and feed heavily in early August because of the new summer adults. If you plant fall brassicas close to your spring crops, you make it easy for these beetles to find food. Fall broccoli, cabbage, kale as well as greens such as arugula, bok choi, nappa and salad mix can get heavily damaged or even killed by flea beetle feeding. However if you manage your plantings so that fall brassicas are in a different, separated field than spring crops, you can significantly reduce your problems in fall crops. How far? As far as possible - any distance helps. Barriers such as forest, streams, roads, houses, are helpful. Shorter distances delay the arrival, longer distances delay and reduce the population enough to reduce or eliminate the need for row covers or sprays. At the UMass Research Farm in South Deerfield, flea beetles in brassica crops are still very active and new emergence has been detected. We have succession plantings of brassica crops close together - but in our case, it is on purpose! In conjunction with researchers and farmers in NY and VT, we are testing the use of komastuna as a trap crop around the waxy type of brassicas (broccoli, kale, collard, cabbage, etc). The whole perimeter is planted to one or two rows of komatsuna (a Brassica rapa), which is highly attractive to flea beetle. On an organic farm, the border can be sprayed with Entrust. The organic farm that is testing this (in combination with field rotation to reduce the pressure) has avoided the need for sprays on the main crop. However, greenhouse transplants required a non-heating row cover to keep flea beetles off the seedlings before they reached the field because the greenhouse had a hefty population of flea beetles.
Late Blight Threatens Potatoes [Modified from a report by David Handley in his Sweet Corn IPM Newsletter] Late Blight, caused by Phytophthora infestans, has been found in some commercial potato fields in Maine this summer. This disease can kill all of the plants in a field and ruin the storage life of any surviving tubers. Infections are not limited to large fields. Small plantings can be infected as well. Tomatoes are also susceptible to this disease, and the impact can be just as devastating. Symptoms of late blight start as water-soaked areas on the leaves, usually in the lower portion of the plant. Symptoms tend to first appear in low, poorly-drained areas of a field. The lesions eventually turn black and may have white, fluffy mycelium showing on the underside. [you can sometimes induce the growth of the fluffy mycelium by taking an infected leaf and putting it in a plastic bag over night. This can serve to get an ID]. Lesions on the stem may be brown or black and will eventually lead to the death of the plant.
Infected tubers will have corky lesions that extend into the tissue, and which will eventually lead to soft rot in storage.
Successful management of late blight relies on an integration of the following tactics:
1. Most important is eliminating the source of the pathogen. In Maine Late blight only survives the winter on living tissue such as the potato tuber. Eliminate cull potatoes and volunteers, and plant only healthy seed tubers.
2. Using resistant cultivars when possible and as they become available.
3. Scouting locations where late blight might appear first.
4. Using a forecasting scheme to gain early warning of weather that is favorable to disease and to adjust frequency of scouting and fungicide spraying accordingly. Copper based fungicides that meet NOP standards are the most effect spray available to organic producers. See <http://www.umaine.edu/umext/potatoprogram/> for details on scouting and forecasting info.
Celery- Cercospora blight (Cercospora apii) Symptoms are primarily on the leaves and a bit on the petioles. It starts as chlorotic spots on both lower and upper surface but quickly the spots enlarge and turn brownish and papery in texture. The disease is both seed and soil- borne and it can survive more than two years in seed. It is favored by humid weather. Make sure your seed is clean. Hot water treatment (48 c for 30 minutes) works. Rotate to fields that have been free of the problem for at least two years. Destroy diseased plants.
DIAMONDBACK MOTH: The diamondback moth is one of three caterpillars that feed on crucifers. The cabbage looper is less common and the imported cabbage worm is so common everyone knows to look for the white moths and the large green caterpillar and its damage. But, even though the diamond back moth has only spotty occurrence when it does occur its damage is devastating and growers must know to look for it and manage it.
The tiny caterpillar, which is sort of pointed at both ends and is green and has a dark head and wriggles when disturbed, eats holes in the leaves……lots of holes. Leafy crops such as kale is quickly ruined. The adult sort of looks like a jet plane to me, except with folded wings and is flighty and hard to find.
The pest does not overwinter here in Maine. Moths are carried north on favorable winds and I have seen them in two locations near the coast this year. Even small infestations should be controlled because they can build to epidemic levels in just a generation or two and 3-5 generations in a season can occur.
Bt works well on the larvae. Bt works well on all three caterpillars, but remember only spray when the pest is there and you need to control it. Entrust works well too, but is quite expensive in comparison to the permitted Bt products.
Also, be sure to destroy crops after harvest so they do not serve as a breeding ground of future generations.
HORNWORMS: Hornworms are probably the most destructive insect attacking tomatoes and they are out in force now both in hoophouse and field 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 that look more like bites of a furry animal than an insect. Look now for the damage and the frass which is black pellets laying all around plants hosting hornworms.
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 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)
CORN EARWORM REBOUNDS: [reprinted and modified from the sweet corn newsletter by David Handley]
Fall Armyworm Also Increasing - Protect Silking Corn!
Situation: Early corn harvest is coming into full swing in southern Maine. Development of later corn continues to be rapid with warm weather and good moisture. Insect pressure has increased in most locations this week, which was to be expected with several storm fronts moving in from the south and west during the weekend, carrying moths with them.
European Corn Borer: Moth activity is still low around the state this week, with the notable exception of Lewiston/Auburn and surrounding areas. Larval feeding damage has been fairly low in most fields. Sprays on pre-silking corn for feeding damage exceeding the 15% action threshold were recommended in East Corinth, Oxford, Poland Spring, Wayne and Wells. A spray to protect silking corn from corn borer based on moth captures in pheromone traps was only recommended in Palmyra. Other locations where corn borer moths were over the 5/week threshold were already being sprayed for corn earworm, so no additional sprays were necessary.
Corn Earworm: Moths captures in pheromone traps rose significantly in most locations this week, putting nearly all fields on a spray schedule for silking corn. This week a six-day spray interval to protect silking corn from corn earworm was recommended in Charleston, Lewiston, Oxford and Sabattus. A 5 day spray interval was recommended in Biddeford, Dayton, Dresden, Nobleboro, North Berwick, Readfield and Wayne, and a 4 day spray interval was recommended at in Auburn, Cape Elizabeth, Dayton, East Corinth and Levant. Corn earworm pressure may still increase with any weather fronts coming from the south.
Fall Armyworm: Moths captures in our pheromone traps increased significantly in many locations this week, so we can expect feeding injury from this pest (large ragged holes) to start becoming more prevalent. When feeding injury is found on pre-silking corn it is combined with any European corn borer feeding to determine if control measures are needed. When both types of injury are found on pre-tassel to silking corn, a spray is recommended if the damage is found on more than 12% of plants scouted. Fall armyworm moths may also lay their eggs on leaves of silking corn, allowing the larvae to move into the ears without leaving any visible feeding signs on the leaves that would be observed while scouting. Therefore, if more than 3 moths are caught in a week in a silking field not currently being sprayed for corn earworm, a spray to prevent fall armyworm infestation is recommended. This week, fields in Poland Spring and Wells had enough fall armyworm moths (3 or more) to justify a spray on silking corn that wasn't already being sprayed for corn earworm. XenTari® (Bt-for light infestations) and Entrust® are two materials that offer control and are approved for organic producers.
See the Resource Guide for Organic Insect and Disease Management or the 2006-2007 New England Vegetable Management Guide for details on these pests.
ONION PURPLE BLOTCH: This disease is caused by the fungus Alternaria porri and first shows up as lesions on the leaves that quickly develop white centers. As the lesions enlarge they become brownish purple and get to be an inch or longer. Spores are formed in the lesions and develop quickly in high humidity and warm temperatures. Alternating high and low humidity favor the spores release and they become airborne. The spores do not live long after they are released but when wind moves the spores on to new onion tissue and it is damp from rain, they germinate. The fungus survives between seasons on crop debris.
If this is a regular problem for you I suggest you try a biological control material called Serenade next year. It is a bacteria (Bacillus subtilis) the has proven to sometimes work well against this fungus. See the Resource Guide for Organic Insect and Disease Management for details on this material and efficacy reports. Also, be sure to rotate to a new field free of onion debris as far away from the old field as possible. In years where water is from irrigation instead of never ending rain, make sure to irrigate in ways that minimize hours of leaf wetness. Copper based fungicides may give you some control this season.
SQUASH BUG EGGS ARE HATCHING: The beautiful, copper colored squash bug eggs that you have been looking at on the squash leaves are hatching like crazy now. The nymphs are tiny and numerous. This is the most likely time that Pyganic will do a good job on them, and hitting them before they do damage is a good idea.
Remember, crop rotation and sanitation is critical to keeping populations of this pest small. Next year avoid putting cucurbits back in the same field or near the field where they are this year. Destroy crop debris and hiding places near the fields.
LATE BLIGHT WARNING: [The following warning about late blight has been modified from notices from Steve Johnson in Umaine Coop Extension]
A late blight sighting has been confirmed in the Hartland, New Brunswick area and southern Aroostook County. The growers are aware of the situation. The sites are being handled as appropriate.
Late blight has been reported in Prince Edward Island.
Late blight has been reported in Long Island, New York. Some areas have had 24 inches of rain since planting.
All areas should be on a 5-day schedule.
SWEET CORN: [Reprinted from the Umaine IPM Sweet Corn Newsletter]
Corn Earworm Flight Threatens Silking Corn
Warm Weather Pushes Early Corn into Silk
Situation: Early corn planted under plastic mulch or rowcovers is now in the silk stage in southern Maine, while uncovered early fields are in the pre-tassel to tassel stage. Many late-planted fields are still in the whorl stage, but warm weather and plenty of soil moisture should move things along quickly. The warmer weather has also increased insect activity significantly, and we are now recommending protection for any silking corn in most areas of the state.
European Corn Borer: We continue to see significant European corn borer moth activity around the state, and an increase in larval feeding damage in many fields. Sprays on pre-silking corn for feeding damage exceeding the 15% action threshold were recommended in Auburn, Biddeford, Dayton, Dresden, Lewiston, North Berwick, Poland Spring, and Wells. Borer injury tends to be heaviest in fields with a history of corn production, or near other fields of silage or sweet corn. When corn reaches the silk stage sprays may be recommended based on the number of moths caught in pheromone traps. European corn borer moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving any visible feeding injury that would be noticed when scouting. Therefore, if more than five moths are caught in a week in a field with silking corn, a spray will be recommended. This week sprays to protect silking corn from corn borer were recommended in Lewiston, Readfield, Warren and Wayne. We do not recommend spraying silking fields for European corn borer if they are already being sprayed for corn earworm. Sprays for earworm should control both pests.
Corn Earworm: Moths are being caught in pheromone traps around much the state this week, resulting in recommendations to protect any silking corn in the area. The arrival of this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. Insecticide application recommendations for earworm are based on the number of moths caught in pheromone traps on a nightly basis. The greater the number of moths per night, the more frequently insecticides need to be applied to prevent infestation. This week a six-day spray interval to protect silking corn from corn earworm was recommended in Dayton, North Berwick and Wells. A 5 day spray interval was recommended in Auburn, and a 4 day spray interval was recommended in Cape Elizabeth and Nobleboro.
Fall Armyworm: We have not yet caught any fall armyworm moths in our pheromone traps around the state, and have not yet found any larval feeding damage in the field. This is usually the last serious corn insect pest to arrive in Maine, but it could appear any time now.
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 wholes 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 that 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.
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.
STRAWBERRY ROOT WORM: As foliage grows back after renovation, keep an eye out for feeding of strawberry rootworm (Paria fragariae). Strawberry leaves attacked by strawberry rootworm beetles are riddled with small holes. Some leaf damage occurs in May, but most occurs in July and August. Heavy infestations can reduce plant growth or kill plants.
Although adults of the strawberry rootworm feed on the leaves of strawberry, root-feeding by the larvae is more damaging to strawberry production. Adult strawberry rootworms are brown to black or copper-colored, shiny, oval-shaped beetles with four blotches on the shell-like wing covers. They are 1/8 inch long. The larvae are grubs that are 1/8 inch long, creamy white, with three pairs of legs. Adult strawberry rootworms overwinter in mulch and soil crevices, and become active in May and June. Adults feed primarily at night and hide in soil or mulch during the day. They chew small holes in leaves, and females lay eggs on older leaves near the soil surface. Larvae burrow into the ground to feed on strawberry roots from late spring to early summer. Small to large patches of dead plants may result. New adults begin emerging in mid-summer, and these beetles feed on strawberry foliage through early fall. Scouting for the presence of adult beetles is best done after dark using a flashlight to examine plants. No threshold has been established for this insect, but a population of 10 to 20 beetles per square foot is considered high. As with all the root feeding insects, control of the root feeding stage is very difficult. Therefore, control measures for strawberry rootworm should be directed toward the adult stage. If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and, therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again. The only control that really works for organic growers is to rotate out of the field after one or two years of picking.
POTATO LEAFHOPPER: Check new plantings of strawberries, beans and potatoes now for potato leafhopper (Empoasca fabae). I have seen these in small populations in the Brunswick and Bowdoinham area. Leafhoppers are sucking bugs that feed primarily on the underside of leaves, causing them to yellow between the veins and become curled and distorted. Feeding activity is most serious during the late spring and early summer. Leafhoppers are 1/8 inch long, green, bullet-shaped insects that take flight quickly if disturbed. The nymphs are light green and do not fly. Nymphs are easily identified by their habit of moving sideways when disturbed. Insecticides should be applied only when large populations of nymphs are noted on the leaves or symptoms first become apparent. By the time severe symptoms are seen it is too late to do anything. I believe the only material organic growers have that works is Pyganic, but if you think something else works let me know and I will pass it on.
BEANS: Mexican bean beetle has arrived in snap beans.. Look for coppery brown, spotted adults that look like large ladybeetles, yellow-orange egg masses, or bright yellow, oval spiny larvae. A beneficial insect, Pediobius foveolatus, is now commercially available for Mexican bean beetle control. This small, non-stinging, parasitic wasp attacks and kills Mexican bean beetle larvae. The parasite does not overwinter here, but provides excellent long-season control of the beetles. This wasp has been tested in snap beans and soybeans in New Jersey and Maryland. A single release, timed so that wasps can attack bean beetle larvae, can provide control. Wasps reproduce in the field and are still present when the second generation hatches out. To pronounce Pediobius, say "pee-dee-oh-bee-us". To purchase Pediobius contact:
ARBICO, 800-827-2847 (AZ), http://www.arbico.com/
The Beneficial Insect Company (NC), 336-973-8490
Rincon Vitova (CA), 800-248-2847
The Green Spot (NH), 603-943-8925
For more information, you can contact: Carol A. Holko, Maryland Department of Agriculture, Plant Protection and Weed Management Section, 410-841-5920, http://www.mda.state.md.us/plant/mex.htm
LOOKOUT: The early season pests are winding down and it is time to start scouting for some mid season pests that could wipe you out if you wait too long to respond. There have been reports of minor outbreaks of potato leaf hopper. You have to spot this pest early if you are to save your crop in years of large populations. Scout potatoes and beans for these flighty little critters by brushing the tops of the plants with your hands and looking for bunches flying up. Try to watch one land to verify the pest. European corn borers can be a major problem for potato and corn producers and they are out and laying eggs now. The eggs are laid on the foliage in a scale like pattern containing 15-35 eggs. The best way to monitor is to set up pheromone traps on your farm. If you do not do that you should visit the Extension website where they report the results of the traps they have set up around the state. For potatoes go to: http://www.mainepotatoipm.com/
And for sweet corn go to: http://www/umext.maine.edu/topics/pest.htm
Armyworm has been reported. No major outbreak, but growers should keep a close eye on their grain, corn, pasture, etc.
ASPARAGUS BEETLES: There are two different species, the common asparagus beetle and the spotted asparagus, beetle that occur here in the Northeast. Their life histories and damage is similar. It seems late for me to be talking about these critters because the horrible damage was done last month when the adults feeding on the new spears made them unmarketable. But now the larvae are feeding on the fern and eating of the leaves weakens the plant and reduces next years yields. The adults of both species overwinter in crop residue. Cleaning up the residue in the fall is the main non chemical defense. The adults become active in the early spring and start feeding and laying eggs. The eggs hatch in just a week or two and the larvae of the common asparagus beetle feed on the leaves for three to four weeks and then drop to the ground and pupate. The larvae of the spotted one feeds on the berries. A second generation of adults may start the cycle over again and the next generation of adults will overwinter. One cultural practice that would have helped is harvesting all the spears through the early spring and cutting them close to the ground. Asparagus is the only crop these beetles eat and so you potentially could starve out the overwintered adults by denying them anything to eat when they wake up. As mentioned above, cleaning up crop residue and debris near the bed in the late fall will deny them shelter for the winter. But now, if the population of larvae, which look like tiny gray slugs, is very large and destroying the ferns, you should spray with a botanical insecticide such as pyrethrum.
[Cutworms are still around and so I thought this great and in depth report by Ruth Hazzard from UMASS is important to see]
CUTWORMS ON SWEET CORN SEEDLINGS (Reprinted from a UMASS Vegetable Notes). Some growers are reporting serious cutworm damage in sweet corn that is at the seedling stage now. Cutworms can also damage in lettuce, brassicas, peppers, tomatoes, eggplants and other seedlings. On top of crops lost to flooding and soggy soils, this loss is especially discouraging. Corn is especially susceptible at the one to two leaf stage; by four to five leaves, cutworm feeding is not a problem.
Damage and identification. Feeding takes place at night. There may be some leaf feeding, but most often the stems are clipped. There are many species of cutworms that attack vegetables including black, variegated, dingy, spotted, dark-sided, or glassy cutworm. Spotted and variegated cutworms climb and feed above-ground, and black cutworms climb when they are young (less than half an inch long). Cutworms can be difficult to identify. Variegated cutworm has some pale yellow markings on its back, while black cutworm is nearly uniform gray to black with a greasy, rough appearance. (See Pest ID Supplement for photos). The cutworms we took from an infested sweet corn field this week were black cutworms, one of the most common in this area. Adults of all cutworms are moths with dark gray forewings, often with various lighter or darker markings, and lighter hindwings. They are in the same group of moths (noctuids) as the corn earworm, fall armyworm, and cabbage looper, but with very different life cycles and habits. Usually we don't see them since they fly at night. Moths are capable of migrating long distances. Black cutworm moths are reported to overwinter no farther north than Tennessee but migrate north very early in the season (March, April) and lay eggs. Thus, we see damage from their offspring in June. Some cutworms spend the winter in the larval stage as deep as 5 inches (12 cm) down in the soil and they may be present in the soil at planting time, ready to feed on early spring transplants and seedlings. Other cutworms winter in the pupal stage. Adults from these emerge in May or June. Moths emerge from pupae of spring-feeding larvae later in the season. There may be one to two generations per year.
Where are cutworms a problem? Cutworms occur where moths chose to lay eggs and where conditions are good for survival. Females lay eggs on grass leaves, weeds, or the crop residude. Attractive habitats include weedy or grassy areas, and alfalfa. Corn and soybeans are among the least attractive egg laying sites. Black cutworm moths are reported to select low spots in the field that has been waterlogged or flooded. We have had plenty of those type of areas this year! Eggs are also concentrated on low-lying weeds such as chickweed, curly dock, shepherd's purse, peppergrass, mustards such as yellow rocket, or plant residue from the previous year's crop. Note that the above list includes lots of winter annual weeds that grow in the fall - weeds that we often overlook. Larvae feed on weeds - and destruction of weeds just before planting can make the crop more vulnerable, since all other food has been just taken away from the existing population of larvae.
Monitoring. Pheromone traps can be used to monitor the adult flight. To sample cutworms, scout fields when seedlings are young to look for damage. Sample 50-100 plants in groups of 10 or 20. Larvae burrow in the soil and are difficult to find, though searching in the soil near a clipped stem usually turns up a cutworm. Estimate % stand loss to determine need for a spray. Damage may be more concentrated around field edges or in low areas.
Cultural Management. Weedy land harbors the most cutworms, as the adult moths seem to prefer dense plant cover for egg laying. Crop residues may also attract higher populations. Therefore, crops that follow weedy crops, alfalfa, or no-till crops are more likely to be damaged by cutworms. Plant early transplants into fields that had low weed pressure the previous year, especially in the fall, or where crop residue was tilled under in the fall. There seems to be little information about specific relationships between what cover crops are planted in the fall, and cutworm infestations in the following year. Plow fields in spring and keep weed free for at least two weeks before planting to starve young larvae and reduce egg-laying. Avoid planting susceptible crops close to sod, alfalfa or fallow areas. Summer plowing disturbs eggs and larvae and raises them to the soil surface where they are more vulnerable to predation and desiccation. Fall plowing will do the same. Plan rotations to avoid planting vulnerable crops after a grassy sod, and plow sod fields in later summer or early fall. Cultivate frequently to injure and expose hiding cutworms to predators.
Organic options. Insecticide baits made of a concentrated solution of an allowed insecticide, mixed with bran and a bit of molasses have been reported to work. The bait can be sprinkled on the ground near the crops or made into patties that are placed along the rows. Bt sprays (ie, Bt aizawi or kurstaki directed at plant stems and foliage) work sometimes, but not consistently, possibly because large cutworms do not ingest a big enough dose of BT to stop feeding and die before they have caused damage. Collars around each seedling work on a garden scale but are impractical for field scale crop systems. Daily search and destroy missions -- by hand -- are a time-honored "biological" management for small plantings!
Biological management. Probably the most promising biocontrol organisms are beneficial nematodaes, which are available commercially and can attack soil insects such as cutworms. It is important to use the correct species. Two species of nematodes, Steinernema carpocapsae (Sc), or Heterorhabditis bacteriophora (Hb) are often used in combination because they attack insects in different levels of the soil. This works well for cutworms that move up and down. The nematodes are shipped to you on a sponge. You mix them with water and apply to the soil. Follow the instructions that come with them. They can reduce cutworms and last for anywhere from 8 days to several weeks, according to various research trials. The nematodes reproduce in the soil and, if the conditions are good for them, large populations of the nematodes will build up and these will hold the population of cutworms down. Good soil moisture favors survival. Repeat applications may be needed. -Ruth Hazzard (with thanks to the following sources: Capinera, Handbook of Vegetable Pests; Vern Grubinger (UVM), Brian Caldwell (NYS-NOFA),Eric Sideman(MOFGA), Rex Dufour (ATTRA)) Updated June 2006)
BACTERIAL SPOT AND BACTERIAL SPECK OF TOMATO AND PEPPER:
Bacterial spot caused by Xanthomonas campestris pv. vesicatora (Xcv) is present wherever tomato and peppers are grown. In general, Xanthomonas pathovars have narrow host ranges. Xcv consists of different strains that vary in their pathogenicity to tomato, pepper, and nightshade. The bacterium is able to survive on tomato volunteers and can overwinter in diseased plant debris. Seed is an important mechanism for survival and dissemination of Xcv. Disease development is favored by temperatures between 80 and 90 degrees F and by heavy rainfall. The bacterium is spread by wind-driven rain, workers, farm machinery, and aerosols. It penetrates through stomates and wounds created by insects, wind-driven sand, and tools. Xcv affects all above-ground plant parts. On leaves, the spots are generally brown, circular, and water-soaked. Bacterial spot lesions do not have concentric zones or a prominent halo. When conditions are optimal for disease development, spots can coalesce to form long, dark streaks. A general yellowing may appear on foliage with many lesions giving the plants a scorched appearance, and the plants may exhibit severe epinasty. Only green tomato fruit is susceptible to infection and lesions are quite distinct, beginning as minute, slightly raised blisters with a halo that resemble the birds-eye spot caused by Clavibacter michiganense (bacterial canker). As lesions enlarge, they loose their halo and become brown, raised, and scab-like. Lesions on ripe pepper fruit may be scab-like or sunken.
Bacterial Speck of Tomato: Bacterial speck occurs on tomato not pepper. It is a cosmopolitan disease, generally of minor concern in New England, favored by low temperatures and high moisture. The bacterium Pseudomonas syringae pv tomato causes a fruit spot and foliage blight. This bacterium is also seedborne, spreads within fields in the same manner as bacterial spot, and may persist in weed species. Lesions on leaves are round and dark brown to black with a halo that develops with time. Spots may coalesce, killing large areas of tissue. On fruit, small (1/16 inch), dark spots or specks develop with the tissue around them often more intensely green than unaffected areas.
Management of Bacterial Spot and Bacterial Speck: Although the two bacteria are unrelated, their life histories and management strategies are similar.
1. Buy certified seed from a reputable source or use seed treatments to reduce transmission.
2. Produce disease-free transplants by raising transplants in an area where production does not occur. Inspect all purchased transplants carefully and if transplants originate in southern states they should be certified.
3. Rotate fields to avoid carry-over on volunteers or crop residue.
4. Keep fields free from volunteers, weeds, and cull piles.
5. Avoid working in fields when bacterial diseases are present and the fields are wet.
6. Apply appropriate bactericides or combination pesticides. In general, bacterial diseases of field crops are difficult to control with pesticides; copper/mancozeb solutions are most effective When a significant amount of disease is present, pesticides are usually not effective.
Chemical recommendations: There is not much for the organic grower except copper hydroxide (Champion WP): 4 tbs/1000 sq ft ( 0 dh, REI 24 h). Greenhouse and Shade house crops. Begin applications when disease first threatens and repeat at 7-10 day intervals as needed. Do not apply in a spray solution with pH less than 6.0 or phytotoxicity can occur. --(modified from a report by M. Bess Dicklow. In UMASS Vegetable Notes)
STUNTED LITTLE YELLOW PLANTS, WILL THEY RECOVER? It depends. The weeks of rain have set farmers back but also have set the crops back too. There are two major reasons. The first is that the roots of nearly all species of plants must have oxygen available to them and when the soil becomes waterlogged all of the air spaces are filled. Roots stop absorbing nutrients, especially nitrogen. If it stays wet long enough the roots die.
The second cause of the hurt plants has to do with the way nitrogen behaves in the soil. Nitrogen can be found in soil in many forms such as the gas nitrogen, as part of the proteins in organic matter and as ions such as nitrate, nitrite and ammonium. Most plants can only pick up the nitrogen when it is in the nitrate form and some when it is in the ammonium form. In soil that has air and moisture but not too much, nitrogen cycles around these different forms by biological activity and some is always passing through the nitrate form and is available to crops. When the soil is too dry, too cold or too wet the cycling stops or can even change direction so the nitrogen is lost from the soil either by leaching or by reverting to a gas form and goes out into the atmosphere. This may happen only in portions of fields where water puddles.
When the rains of May and early June came some of the nitrate was lost by simple leaching. When the soil became waterlogged and anaerobic the nitrate reverted to nitrogen gas and was lost. If most of your nitrogen was in the nitrate form at this time, it is gone. Folks who use chemical fertilizers will probably have to reapply it. The nitrogen that was in organic forms such as seed meals, fish meal, compost and livestock manure probably will still have much of the nitrogen left because the soil became cold and anaerobic before the bacteria converted the organic nitrogen to nitrate. Farmers just have to wait for the air spaces to reappear in the soil and the bacteria to get to work. Of course, this should have happened in April and so it may be wise to supplement your crops with a bit of available nitrogen while this is happening now in the middle of June. And, non of this will help those crops whose roots died.
Spring in New England is nothing but fun.
MANAGING COLORADO POTATO BEETLE: Colorado potato beetles (CPB) are moving into potato and eggplant crops, and will soon be laying eggs. Some adult beetles spent the winter in last year's potato fields, but most moved into the woods and brushy borders next to these fields, where they burrowed into the soil up to a depth of 12 inches. In spring the beetles have to regrow their flight muscles before they are able to fly. At first they search for food plants by walking from the field edges. This is why the edge of non-rotated crops are attacked first. If beetles do not find host plants via walking they will fly some distance in search of food. Once host plants are found adults begin to feed and lay eggs. The beetles will have mated the previous fall or late summer; hence they have no need to mate in the spring to produce viable eggs. However, they do continue to mate in spring. The bright yellow eggs are laid in clumps that average 30-35 eggs, generally on the undersides of leaves.
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. 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. Now is the time to scout for adults, eggs and egg hatch.
Walk your fields and look for CPB adults and eggs. The economic threshold for adult beetles in potato is 1 beetle per 2 plants (or per 2 stalks, in midseason). Eggplant seedlings have a low tolerance to damage. 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 the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch. Larvae go through four stages before they drop to the soil and pupate. 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. Ten days later the next generation of adults emerge and feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites.
Spray timing and thresholds: To prevent resistance the best strategy is to alternate among classes of insecticides in each generation, and throughout the season. An example would be to use a material such as Spinosad (Entrust), which controls adults and larvae for the first spray, followed by a Bt (Novodor) to kill emerging young larvae. BUT, at this time there is no Bt formulation approved for use in organic systems. NOVODOR IS NOT APPROVED FOR ORGANIC PRODUCTION BECAUSE OF INERT INGREDIENTS. VALENT, THE COMPANY THAT MANUFACTURES IT, AT ONE TIME SAID THEY WOULD REFORMULATE IT TO MEET ORGANIC STANDARDS, BUT SEEM TO HAVE CHANGED THEIR MIND. GIVE THEM A CALL AND TELL THEM HOW IMPORTANT IT IS TO ORGANIC GROWERS (1 800 323 9597).
If you are not organic and are using Bt (Novodor), you want to make the first application when 20- 30% of the eggs have hatched. If you are using spinosad (Entrust is the organic formulation) you can wait until more larvae have hatched, when the oldest larvae reach the third instar, when they are about 1/3 inch long. Applications made at this time with Entrust will kill all the larvae that have hatched up to this point. The 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. Thresholds established in the Northeast for eggplants from seedling to fruiting stage include: 15 CPB per 10 plants (Rutgers) or 2 small/1 large larvae per plant (<6 inches) or 4 small larvae /2 large per plant (>6 inches) (Cornell). In eggplant, in addition to defoliation, beetles sometimes clip the stems of flowers or flower buds. This directly reduces fruit formation and marketable yield. On the other hand, potatoes can tolerate 20% defoliation without reduction in yield (or even more, later in the season and depending on cultivar).
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 with a foliar insecticide. In eggplant or tomato, the perimeter border can be an Italian eggplant type, which is more attractive to both CPB and flea beetles. Treat only the border, as soon as beetles arrive.
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. -(modified from an article in UMASS Vegetable Notes by Ruth Hazzard. R Hazzard says thanks to sources including: D Ferro (Umass Amherst), J. Mishanec (CornellUniversity), J Boucher (Univ. of Connecticut). Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in con*ict with the label.
RASPBERRY WINTER INJURY: Even though red raspberries are the hardiest of the bramble fruits, we are seeing a lot of what appears to be winter injury on overwintered floricanes of summer-fruiting raspberries throughout the state. Fall-bearing cultivars whose canes are mowed every spring are not sensitive to winter injury, and aren't showing damage.
What does winter injury look like? The most common symptom of winter injury is dead canes or dead tips on overwintered canes. In some cases, canes may leaf out later than expected, or not at all. You may also see dry, cracked areas along the length of dead or damaged canes. Milder winter injury can also affect vascular tissue so that canes can leaf out and appear healthy, but when temperatures warm up and canes start to grow rapidly, the damaged vascular tissue cannot supply laterals with water, so the laterals collapse.
But I thought we had a pretty mild winter… Winter injury can be caused by very cold temperatures (-20C), but can occur even when temperatures are not that low. Last winter was mild, but we did experience some of the other conditions that make winter injury more likely:
What to do? Now that healthy canes have leafed out completely, prune back and remove dead winter-killed tissue and canes. In future years, the following precautions can help to prevent winter injury:
- A very warm wet late fall. In most parts of NH, our first fall frost happened late - the end of October. Until then, perennial plants just kept growing, and did not have time to transition slowly and gracefully into dormancy. The rapid transition to winter occurred before plants were fully dormant and tissue was more tender than normal.
- No snow cover. Winter injury is caused by wind desiccation as well as by very cold temperatures. Snow cover does doubleduty, insulating canes from lower temperatures and protecting them from wind and drying out. Very little snow during the winter meant that canes were more exposed than normal.
- Large temperature fluctuations. Although this may not have affected raspberries as much as other perennials, warm spells followed by sudden drops in temperature can injure plants that have started to break dormancy during the warmth. We had a couple of large (>50 degrees) sudden drops in temperature in January and February that could have played a role.
[adapted from the New Hampshire Vegetable and Berry Newsletter by Becky Grube and George Hamilton]
- Choose a site well-sheltered from prevailing winds.
- Grow hardy varieties (Boyne, Killarney, Nova are very hardy; Titan, Taylor, K81-6, and Lauren are less so).
- Do not over-fertilize. Mature plantings usually require about 50-60 lbs actual nitrogen per acre per year.
- Do not trim new canes (primocanes) back after July 1.
- It's also important to minimize other stresses. Damage by voles, soil-borne diseases like Phytophthora, and cane diseases like anthracnose and spur blight all weaken canes and predispose berries to winter injury.
Steve Johnson from Umaine Extension sent this interesting note out.
We are trying a new approach to late blight risk. The table below is a compilation of practices and events that can put a field at risk for late blight. THESE RISK RATINGS ARE NOT SEVERITY VALUES. RISK RATINGS ARE AN INDICATOR OF THE POTENTIAL THREAT FOR LATE BLIGHT.
I've summarized some current risk issues:
All fields have accumulated 1 risk rating
Most fields have accumulated an additional 4 risk ratings (total of 5)
Some fields have accumulated yet an additional 1 risk rating (total of 6)
+ 1 each
LB present in Region last season All fields included
LB present in Area last season Most fields included
LB present on Farm last season Some fields included
≥ 18 Severity Values met Most fields included
+ 1 per day per event
Weather forced longer spray interval than recommended Most fields included (or will be by Monday June 12)
SW field capacity > 0.95 % Most fields included
Some fields may have additional risk ratings based on the below practices or events.
+ 1 each
Cull piles in area
Seed was cut and held for ≥ 3 days
Seed was not treated with MZ
OK ≤ 3
We are in a risky situation with the predicted upcoming weather. Friday morning we had accumulated 20 hours of infection conditions. By Saturday morning that is expected to 44 hours and by Sunday morning, 68 hours. That alone will accumulate more than 18 severity values. As soon as possible, coverage need to be put on emerged plants. Those that have fields in the "some fields" category or those that have any of the additional risk included here:
+ 1 each
Cull piles in area
Seed was cut and held for ≥ 3 days
Seed was not treated with MZ
should consider the addition of cymoxanil to the tank mix. At this point, timing is more critical that the rate of material.
Keep current by calling the hotline (760-9ipm) or visiting the website:
and clicking on the Pest Alert link.
The complete table for risk ratings (Late Blight Risk Table.pdf) appears on the Pest Alert page
Steven B. Johnson, Ph.D.
Crops Specialist and Extension Professor
University of Maine Cooperative Extension
P.O. Box 727, Houlton Road
Presque Isle, Maine 04769
The wet weather continues and it is time to start thinking about diseases that were a problem on your farm last year that may be hard to avoid this year, especially if your crop rotation and sanitation were not what they should have been. There was a very nice warm string of days just at the right time to get the warm weather seedlings out in late May, but now they have been sitting in wet soil with wet leaves and the cool air has delayed growth. I think this may be a year of spots.
Tomato Spots: The three most common problems with tomatoes grown in the field in Maine are Early Blight, Bacterial (Spot and Speck) and Septoria Leaf Spot.
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 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 this 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.
Cucumber Beetle: I have had the first report of striped cucumber beetle. These 1/4 inch long, black and yellow beetles spend the winter sheltered under plant debris near and in the field where cucurbits were grown last year. The overwintered generation can zero in on newly planted seedlings and eat all of the leaf tissue in a day. Once the plants attain 4-5 true leaves they are more tolerant of the feeding, but the beetle still can transmit bacterial wilt and populations should be kept small.
Crop rotation and sanitation help a great deal in avoiding the overwintered generation. Floating row covers are very effective for protecting young plants. Remember to remove to weed and then take away when the crop flowers to allow pollination. Trap cropping is possible with this crop and pest (see the Resource Guide for details). Pyrethrum will kill the beetles, but they are good fliers and often take off and return when you leave. There have been good reports from growers using Surround sprayed on seedlings before transplanting.
Root Weevil Management
From info supplied by Richard Cowles, CT Agricultural Experiment. Station; Peter Shearer, Rutgers Cooperative Extension; and others
Despite the open winter, we have observed some plantings of strawberries infested with the grubs of black vine weevil and strawberry root weevil this spring. It is not too late to put on an application of nematodes to control the grubs (optimal timing is about mid-May but we have been so wet and cool that I bet it may still work). Two species of nematodes appear to offer the best control of root weevil grubs. Heterorhabditis bacteriophora (Hb) appears to be the best candidate for control of root weevils when the soil temperature is above 60 degrees ('J-3 Max Hb' from The Green Spot; 'GrubStake HB' from Integrated Biocontrol Systems; 'Larvanem' from Koppert Biologicals). Beneficial nematodes can also be applied in late summer (August 15 - September 1), and in that case, Steinernema feltiae ('Nemasys' from Griffin Greenhouse Supply, 'Gnat Not' from Integrated Biological Control Systems, 'Entonem' from Koppert Biological) should be considered in northern locations since it tolerates cooler soil temperatures and completes its life cycle quickly.
Once the grubs begin to pupate (usually early June) nematodes should not be applied, because they do not attack the adult (beetle) stage. Once the adults become active bifenthrin (Brigade) will provide some control if used at the highest labeled rates. The best timing for this spray is at night during the peak feeding activity of adults, before they start laying eggs, or about 1 week before harvest ends. Neem-based products containing azadiractin (such as Aza-Direct) may be acceptable for organic production, and while neem will not kill the adults it can disrupt egg-laying if applied at high rates at least twice.
Nematodes are living organisms and they can be killed if they are misapplied. Order nematodes ahead of time and be ready to apply them through a sprayer or irrigation soon after they arrive, refrigerating if delay is necessary. Do not apply nematodes using a sprayer with a piston pump. Use clean equipment, removing all screens finer than 50-mesh. Apply nematodes in early morning or evening in a high volume of water to already moist soil, pre-irrigating if needed. Apply another π inch of irrigation after application to wash them onto and into the soil. Although references suggest rates of several billion nematodes per acre, I found researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of about $100 to 200 acre depending on volume and source. Ironically, nematodes probably work best in the worst weevil-infested fields. High populations of weevil larvae allow explosive growth in nematode populations, while low populations of larvae may not permit efficient nematode reproduction. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven't taken over the roots.
Root weevils cannot fly, so they infest new plantings by wandering into fields from surrounding weedy and woodland vegetation, or in large numbers from recently plowed, infested strawberry plantings. Even plantings several hundred feet away can become generally infested as a result of mass migration from plowed fields. A good rotation program with substantial distance between strawberry fields can help to manage root weevils. Also, when turning under old, infested strawberry plantings, it is critical to leave a row or two at the perimeter of the field as a trap crop to protect other plantings. Adult weevils will be intercepted in these rows before they leave the field and thus lay their eggs where the larvae will not do any damage. At the end of the season the trap rows should be turned under prior to planting winter rye. Do not spray the trap rows as this may repel weevils and result in more migration to other fields.
Some Beneficial Nematode Suppliers:
The Green Spot: 603-942-8925 or www.shopgreenmethods.com <http://www.shopgreenmethods.com >
Griffin Greenhouse Supplies: 978-851-4346 or www.griffins.com <http://www.griffins.com >
Integrated Biological Control Systems: 888-793-4227 or www.goodbug-shop.com <http://www.goodbug-shop.com >
Koppert Biologicals: 800-928-8827 or www.koppert.com <http://www.koppert.com >
SEEDCORN MAGGOT AND WIREWORM DAMAGE ON EARLY CUCURBIT TRANSPLANTS
Seedcorn maggot and wireworm are occasional pests on cucurbits. This year, it is possible that unusually warm temperatures in April followed by unusually cold and wet conditions in May has favored these pests. Pest alerts from Maine to Indiana have noted this pest as a problem. We have seen damage in Massachusetts in one early melon field. Symptoms are wilted plants and collapsed, rotting stems. These pests feed on the roots and bore into stems at the ground surface. They feed on the internal tissues and kill the plants. In the field if you find wilting plants and no clues of insect feeding or diseases on the aerial parts, then dig up the plant and check for seedcorn maggots and wireworms. The seedcorn maggot is yellowish-white, legless, with a pointed head and is about 1/4 inch long when fully grown. The wireworm is slender, jointed, usually hardshelled, with three pairs of legs, and tan brown in color. This week at a farm in the Connecticut River Valley, we found maggot pupae which are 1/4 inch long, oblong and tan or brown. Symptoms were noticed by the farmer last week, when maggots were actively feeding. Once maggots pupate, the damage is done. A new crop of adults will emerge in 7-14 days. Wireworms were also found, but maggots were most numerous. Cold conditions which inhibit crop growth but favor the maggots encourage this pest. Once a field is infested with seedcorn maggot or wireworm, not much can be done to cure the problem. Replanting decisions should be made based on estimates of the size of the maggots infesting the field. If the maggots are smaller than 1/4 inch long we recommend waiting 10 days to replant, if they are larger or equal to 1/4 inch long, plants can be replanted after 5 days. If wireworms are found, wait to replant until soil temperatures are above 70 degreesF. The field in which we found damage in Massachusetts was planted with melon transplants in early May, after tilling in a healthy cover crop, applying plastic with straw mulch between the rows, and putting row cover on hoops over the entire crop. It appears that the seedcorn maggot flies emerged, mated and laid eggs under the row cover or laid eggs after tillage but before transplanting. Maggot flies are attracted to the odors given off by the microorganism associated with decaying organic matter or diseased plants. For growers who want to improve their soil by incorporating large amounts of biomass in the spring, or use reduced tillage systems, it may be important to figure out how to avoid this risk. Waiting until soil is warm enough to encourage rapid germination and crop growth may help. Disking cover crops at least four weeks before planting may make them less attractive. As reported last week, seedcorn maggot attacks seeds and seedlings of many vegetable crops. After May and June this pest is rarely a problem.
Adapted a bit and reprinted from UMASS Notes from an article adapted by Ruth Hazzard from May 26, 2006 article by Dan Egel, Chris Gunter, and Frankie Lam, Vegetable Crops Hotline, Purdue University Cooperative Extension Service
Once again it is a cool and damp spring and I want to stress that farmers and gardeners need to watch the sky as well as the calendar. The calendar says beans and corn should be in the ground and germinating, but the soil is cold and anaerobic and seeds are rotting, if not being washed away.
SEEDCORN MAGGOT: Peas, beans, corn, potato sprouts and even cucurbits in the greenhouse are attacked by the larvae of this fly. They are yellow-white maggots about a quarter of an inch long and sharply pointed at the head end. The symptom is usually that you see no germination, and when you dig around you may find nothing left or may find the maggots burrowing into the seed. Sometimes the seed germinates but only a weak or partially eaten plant is seen. The injury is most likely to occur in cold wet seasons where the germination is slow, and also in soil high in organic matter.
The attack is early in the spring because the critter spends the winter as pupae in the soil or maybe free maggots in manure or unfinished compost. The adult is a grayish brown fly only about a third of an inch long. It emerges in early spring and deposits eggs in rich soil, compost piles or near seeds and seedlings. Exposed peat or potting soil mix of transplants can also serve as attractive sites for females looking for a place to lay eggs. There are a few generations each season.
The best method of dealing with this critter is to do everything you can to encourage quick germination and rapid growth. In the cold, wet soils we have this spring the seeds are just sitting ducks. Shallow planting helps when conditions are poor. Best yet, wait for things to warm up and dry out.
PILL BUGS: (NOTE: This report below is from a grower in Little Compton, RI but as I was copying it I got a call from a grower right here in Belfast, Maine.) We are learning a hard lesson about long term problems with greenhouse tomato production. Pill bugs showed up in massive numbers this season and almost destroyed the whole crop. Since we always use a fair amount of compost in our operation we have become accustom to their presence over the years and always thought them benign. This year that change radically and we noticed they were almost twice the size of one in the past. We graft our tomatoes and they first attacked the lower grafted sections. It first appeared like a scuff mark. I first thought an employee had been too rough with the plants when suckering. Then quickly there after they were eating right through to the inner core of the plants structure! When we figured out who the culprit was we gave them a hardy shot of Pyganic and found thousands belly up all over the house. One of our problems is that we use black plastic to control weeds under our tomato plants. This is providing them with a perfect breeding ground! After this season we will do that no more. At best we have them at bay. They are still feasting on the leaves that touch the ground and I can no longer get the spray where I would like. We are hoping to get some nematodes to do some control on them during the off-season. Some Quebec growers are having similar problems. With these critters we have yet another reason for looking over our shoulders. (Editor's note, this just in from Quebec: they are experimenting a plastic collar, like a cone around the base of the tomato plants, to deter pill bugs. It is made from greenhouse polyethylene, 3inches high. The whole thing is keeping upright with Tanglefoot glue, which is a natural resin that never dries. It is important to put glue at the base of the cone to prevent the entry of pillbugs there. Pillbugs seems not able to climb on a clean plastic.) (Taken from Vern Grubinger's Vermont Notes)
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. [Different species of flea beetles feed on the tomato family of 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. Occasionally in tender greens such as arugula, tarnished plant bug feeding may be confused with flea beetle feeding. In addition to the shot holes from flea beetles, there may also distorted leaves that are typical of TPB feeding, which injures leaf tissue when leaves first emerge.
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 close by ensures a
high population in the spring. 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, 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, black plastic bags filled with soil, or some other method.
Spinosad (Entrust is organic formulation) is proving to be an effective in suppressing flea beetles and reducing damage. A supplemental label has been issued in Massachusetts for flea beetle suppression in brassicas; other states may also have this [not Maine, I just checked], but in all states the product is labeled for use in brassica crops. Pyrethrin (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. 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.
This year, with funds from a SARE Partner Grant, we are testing a Perimeter Trap Crop (PTC) system at several farms in NY, MA and VT. We are using more attractive greens (Brassica rapa types) as a trap crop for cabbage,
collard, kale or broccoli (Brassica oleracea). Komatsuna is our choice for the perimeter trap because it is highly preferred compared to cabbage, seed is inexpensive, growth is rapid, and the crop continues to produce new, attractive foliage over a long period. Borders are being sprayed with spinosad when beetles first arrive. Our first week of observations show promising results: heavy feeding in the komatsuna, and virtually none in the cabbage. We'll keep you posted! We have also gained the insight that woodchucks prefer cabbage over komastuna. In fact, they won't even touch that nasty light green crop, but will walk right past it to chomp down cabbage seedlings. If you are interested in trying PTC for cabbage, kale, collard, or broccoli please feel free to call Pam Westgate or Ruth Hazzard at (413-545-3696) for more information. (modified from Mass. Veg. Notes by Ruth Hazzard)
This is the first Report Report for the 2006 growing season. Again I want to thank the Cooperative Extension folks in New England for sharing their great reports with me and allowing me to modify them for my report. If I do not say where it comes from then the report is my own.
If you are a MOFGA certified grower then you will only receive the next Pest Report if you reapplied for certification for the 2006 season. If you did not reapply and would like to receive the Pest Report anyway, contact me.
Organic Crop Specialist for MOFGA
PYTHIUM ROOT ROT: Pythium is one of the most common fungi found in roots of greenhouse crops. It is a natural inhabitant of the soil and can survive there indefinitely as well as in debris in the greenhouse. Stunted growth and wilted plants are common above-ground symptoms caused by Pythium root rot. To examine plants, remove plants from pots and examine roots. Healthy roots are white and firm; decayed roots may be dark colored and the rotted outer covering of the root slips from the central core.
Growers having re-occurring problems with Pythium, should review their overall production practices including fertilizing, watering and media handling. Over-watering and excessive fertilizer levels promote Pythium. Good sanitation is crucial for prevention. Keep hose ends off the floor, wash hands before handling plants and avoid contaminating growing medium.
Since symptoms can be confused with other causes such as high soluble salts or other diseases, suspicious plants should be diagnosed through your University diagnostic lab. There are several materials registered for Pythium including potassium salts of phosphorous acid (Alude), which works by stimulating the plant‚s natural defenses, and the more traditional fungicides Aliette, Banol, Banrot, Subdue, etc. Apply treatments as a drench, following label directions. After application, irrigate with additional water to move the fungicide into the root system. Note that about half of most isolates received at the UMass diagnostic lab over the past few years have been resistant to Subdue. Some growers have reported some success using a rescue treatment of hydrogen dioxide (ZeroTol) drench, followed by a fungicide treatment, the theory being that ZeroTol will knock down the pathogen in the soil and the fungicide will act as a protectant. A study is currently being conducted to determine whether growing media affects the activity of hydrogen dioxide. -Adapted from article by Tina Smith, UMass Extension
CUTWORMS: This is the time of year to start thinking about cutworms which often become a real challenge especially for transplants, carrots, onions. 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 makes a good barrier. I have received good reports about making a bait from bran, a Bt solution and molasses and then sprinkling it or making patties and putting them along the row of effected crops.
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 shortly 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).
Another method for managing cutworms may work in some systems that can delay planting. The cutworm is the caterpillar of a moth. Some species fly in the fall and lay eggs and other fly in the spring. In any case, the caterpillars are feeding early in the spring and if there is no food they will starve. Keeping a field completely free of weeds and crops for a few weeks in the spring may work.
CABBAGE ROOT MAGGOT: Watch for cabbage root maggot eggs, especially on transplants. Flies spend the winter as small brown pupae in the soil. Adults emerge in spring (around the time forsythia flowers) and seek out crucifer plants to lay eggs at the base of the stem. Adults can travel considerable distance in search of host plants (1/2 to 1 mile). (Onion growers should also watch for onion root maggot activity at this time. See below)
Hot dry soils are not a favorable environment for maggot egg survival. Eggs are killed when temperatures exceed 100 o F, and are also subject to desiccation under dry conditions.
Recent research by Tony Shelton at Cornell University produced a degree day model for cabbage maggot emergence in New York State. According to the model, the first emergence of cabbage maggot occurs at 160 degree days +/- 8 degree days (DD). 25% emergence occurs at 203 DD +/- 3 DD, 50% emergence occurs at 251 DD +/- 8 DD, 75% emergence occurs at 304 DD +/- 37 DD and 95 % emergence occurs at 387 DD +/- 8 DD. We do not know if this model fits for New England maggot flies, as there can be regional variations, but it gives an estimate. For growing degree day information in Maine go to http://pronewengland.org/AllModels/MEmodel/RADARME-Monmouth.htm
Growing Degree Days are calculated by taking the average of the maximum and minimum temperatures for the day (Max + Min /2) and subtracting the base temperature (either 50 or 55 oF for most plants and insects). Below the base temperature, growth and development are minimal.
Cabbage root maggot flies are smaller and more delicate than a housefly, and can often be seen moving from plant to plant in early crucifers. To monitor for adult flies, use a flat water-pan trap painted bright yellow (Federal Safety Yellow), placed on the ground in the field. These can be made from any sturdy plastic dish, or purchased. Add a drop of soap to break the surface tension. Flies are attracted to the yellow color and to the moisture. Yellow sticky traps can also be used - these are placed vertically on stakes, near the soil. Check traps twice weekly. This will tell you when the flight peaks, and when it declines. Flights in Maine decline after late-May and many June and later plantings do not need protection.
Floating row covers provide an effective barrier against this pest. Use in a rotated field only, as flies overwinter in fields of late season crucifers, including crucifer weeds. Remove and replace in order to weed. If covers are not a practical option, and eggs are found by scouting, 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. This assumes some soil moisture is present in the upper layers of soil. --Modified from an old report by Ruth Hazzard, UMASS
ONION MAGGOT: The onion maggot is in the same genus as the cabbage maggot and has very similar habits. It is one of the most serious pests of onions and can wipe out an entire crop (it wiped out my entire crop in my garden 2 years ago). Onion is the preferred host and related crops such as scallions, garlic, leeks and shallots are only occasionally infested. Wild onion is not an important host either.
The greatest damage is caused by the first-generation larvae that attacks young seedlings in the early spring. They move up rows to new plants as they devour the young seedlings quite quickly and need more food. The first symptom seen in very young seedlings is a slight wilting of the plant. Later they will simply disappear. Plants attacked at later seedling stages will turn a grayish yellow and wilt and will later detach at the ground level as the maggot consumes everything below ground. Onion plants attacked later are rarely killed and fewer plants are attacked as the maggot does not move to new bulbs. However, plants attacked at the later stage are likely to have misshapen bulbs and usually are attacked by fungi and rot.
The onion maggot overwinters as a pupa in the top five or so inches of soil. When spring soil temperature rises above about 40 degrees the overwintering pupae begin to develop and, depending on the weather, in a number of weeks the adult onion maggot flies will emerge and fly around and mate. Later they will search for onions to lay eggs around. Eggs are laid around the base of onion plants and the resulting larvae crawl down to start feeding on the roots. There can be three generations in a season.
Adults of later generations disperse very little from onion fields so crop rotation is a very important tool for avoiding infestations. Good sanitation is very important because cull onions will attract flies that will lay eggs that result in overwintering pupa. Damaged onions are the preferred site for egg laying so avoid mechanical damage to onions and dispose of any damaged onions rather than leaving them laying around the field. Discing onion fields in the early fall when the flies are still active actually makes things worse because it makes many pieces of onions and so increases the number of sites for egg laying. Ash and diatomaceous earth around the base of onion seedlings may deter egg laying and maggot survival.