"Great problems call for many small solutions."
- Wendell Berry
  You are here:  PublicationsPest ReportsPest Reports - 2012   
October 23 | August 31 | July 27 | July 17 | July 5 | June 29 | June 7 | May 30 | May 25 | May 15 | May 1
Show as multiple pages

MOFGA's Pest Alert - October 23, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Another Garlic Pest - Bulb mites (Rhizoglyphus spp) - It is garlic planting time and we thought we saved the most beautiful heads for our seed. But, when we broke open the heads we were shocked to see the amount of damage to many of the cloves. Again, this year has proved to be a very challenging growing season for a handful of crops. This time it is garlic. I have never before seen this level of damage by bulb mites. And now that my awareness has been raised, I am getting calls from other growers seeing this damage and wondering what it is.

The mite itself is nearly microscopic so it is not a surprise that growers cannot figure out the culprit. Of course, Becky can see the little critters, but I had to use my dissecting microscope. They live down in the tiny, tight space between the cloves or between a loosened wrapper and the clove. If you see damage similar to the picture below, carefully dissect the lower part of the head of garlic, especially down near where the roots and the bulb come together and look under layers of scales. With a hand lens you can identify the bulbous shaped mite. In addition to the mite, we also found thrips living under the scales of the garlic. I am not sure yet whether this thrips is contributing to the damage, or is a predatory thrips feeding on the mites. I will get samples to experts and figure it out soon, so stay tuned and be sure to come to MOFGA's day at this years Agricultural Trades Show (at the Augusta Civic Center, January 8 - 10) where I will again do a talk on pests of the 2012 season.

Garlic and onions plants are not only damaged from the direct feeding by bulb mites, but also by pathogens to enter through the wounds caused by the mites. My garlic that was wounded had Rhizopus (black bread mold) and Penicillium (blue mold) growing in some of the wounds.

This bulb mite has a wide range of hosts, including many flower bulbs. It sure loves garlic. These mites are shiny, creamy white. They have four pairs of legs that seem to be more forward than on most mites, making their rear end look bulbous. They survive the winter in crop debris and decaying vegetation in the field, and in heads of garlic. Hot water treatment of the bulbs is recommended in lots of literature. Contact me if you want the details. But, I would not recommend it after the stories I have heard this year with growers who hot water treated garlic to control the bloat nematode only to find they killed the garlic and it did not sprout.

Crop rotation, sanitation, and planting clean seed is the only recommendation I have at this time. And of course, at this time the seed you have is probably what you will plant, so at least plant the cleanest of it. Try not to plant the cloves infested with mites. Avoid planting in fields with lots of decaying vegetation, especially cole crops which can harbor very high populations of the mite. Fallow fields with completely decomposed organic matter would be best.

MOFGA's Pest Alert - August 31, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist


Autumn is approaching and the farm fields and gardens are showing signs of getting tired. This is the time of year when crops run out of nutrients, succumb to disease or insects, or both, and often get hidden by the late summer weeds. It is also a time of great bounty. Some days I look out in wonder at how much we produced, and other times I look out and wish we did better. Lots of crops are going down or are gone. If this is happening to you and you are wondering why, you can go back and read the earlier Pest Reports of the season and figure it out. Here is a summary of some of the problems predicted and noted that are very obvious now.

By the way, if you would like to see pictures of these problems and be part of the fun and discussion, come to the Common Ground Fair, which begins three weeks from today. On Sunday, September 23, at 1:00, I will present a wrap-up of the pests of 2012.

Some Highlights of 2012:

Spotted wing drosophila on a tomato. Photo by Eric Sideman.

The big problem with spotted wing drosophila (SWD) that we feared would arise, did. The SWD is laying eggs in all sorts of soft skinned fruit as I write (see the July 17 Pest Report for details). This morning Becky sliced open some raspberries to see, and sure enough, larvae.

Late blight (mentioned in many Pest Reports) made it to New England and is wide spread now. It is no where near as bad as in 2009, but if you are one of the unlucky, then it may as well be.

Powdery mildew and squash bugs (June 7 Pest Report) have taken down much of the pumpkin and squash crop.
Thrips (July 27 Pest Report) have taken down much of the onion crop.

Potato leaf hopper (June 29 Pest Report) has taken down much of the potato crop.

The garlic bloat nematode (June 7 Pest Report, and also read the article in the Fair issue of the MOF&G) is showing up in many unsuspected fields of garlic. Be careful buying garlic seed by having the discussion with your provider.

Enough sad stories for this morning. I am going to go water the carrots in the high tunnel and look forward to harvests in January.

See you at the Fair.

MOFGA's Pest Alert - July 27, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

I would still call this a difficult growing season. Many of us across the Northeast have gone from very wet, muddy fields to dry-as-a-bone fields in a short bunch of weeks. Now it is cloudy and rainy and we should all be glad, except late blight has been reported here and there in Massachusetts, New Hampshire, and Maine. With cloudy, damp weather the spores released from this infected fields are able to move in the winds more than 50 miles and survive. In the sunny weather of the past few weeks any spores that got into the wind were likely to die quickly. So, scout your fields carefully and be prepared.

Damage from Onion Thrips. Photo by Eric Sideman.

Onion Thrips - (Thrips tabaci) - Onion thrips are active and taking down onions. If they have been a problem for you in years past, it is time to start scouting for them. They are very tiny and easily overlooked until the onion plants start showing leaves that look as if they have been rasped. In fact they have. The thrips feed by using their moth parts to rasp and pierce the onion leaves, releasing juices for them to feed upon. If the population of thrips is large you will see silvery patches on all the young leaves and when really bad the whole field will look white and silvery and the leaves wither. Obviously onion yields can be greatly reduced because the onion plants loses food and water through the damaged tissue.

Onion thrips hide between the leaves at the base of the onion plant. I find the best way to find them is to pull up a plant and hold it upside down over a white sheet of paper and pull apart the leaves as you shake gently. Even when they are walking about on the paper you will still need to look hard to see the thrips. My eyes are not that good and I need a hand lens to even spot them. The immature thrips are white to a pale yellow, elongated with very short antennas and dark eyes. Remember, tiny. The adult is tiny too, but it has wings. Thrips' wings are unique. They are fringed with hairs. Thrips are very poor fliers, but they do fly when disturbed and get blown in the wind easily. Keep in mind that this means thrips will be blown to new fields downwind. Adults are pale yellow to dark brown.

There are many generations per season and they can be very quick in warm weather. Also, parthenogenesis is common, meaning females that cannot find males produce progeny all by themselves. Each female can produce up to 80 eggs, which tells you that the population can explode quite quickly under good conditions. Good conditions are warm and without heavy rains. Heavy rains wash the weak insect off the plant.

Growers can simulate heavy rains with heavy overhead irrigation. As well as disturbing the insect the extra water will help the rasped onions. Extra fertilization will help too, but this late in the season it is questionable for onion.

Thrips survive in onion debris so clean up after harvest. I have heard that thrips are confused by inter-cropping with carrots. If the natural enemies or the cultural practices fail to keep thrips populations down then you may need to turn to a pesticide. Remember, thrips are often around in small numbers which can be tolerated. IPM practices recommend an economic threshold of an average of 3 thrips per green leaf. When scouting, sample about 50 plants around the field from at least 10 different locations in the field and then figure the average per leaf. Entrust is the most common recommended material. Follow the label instructions and be sure to spray into the leaf axis.

Damage done by thrips

Purple blotch in onions. Photo by Eric Sideman.

Purple Blotch (Alternaria porri) - Purple is a very common and sometime destructive disease that effects onions, garlic, shallots and leeks. Lesions begin as whitish sunken areas that elongate and develop purplish centers. Under favorable conditions (warm with wet leaves) the purple blotch lesions grow large and oval with concentric rings. The lesions may merge and take down whole leaves, and may become covered with brownish spores. The older leaves are more susceptible than the younger leaves.

Onion residue is the source of the disease in the spring. The fungal mycelium and conidia spores persist as long as the onion debris in the field or in cull piles. New conidia are produce on infected tissue in the spring and wind blown or carried in water to the new crop. The leaves have to have liquid water on them for the spores to germinate, but germination is very quick, less than an hour. Symptoms may appear in less than a week after germination and new conidia spores are quickly produced.

Cultural Control - Sanitation is very important to limiting spread. Infected crop debris should be destroyed or buried after harvest. Cull piles should not be kept near the new onion field. Onions should be grown in rotation with non host crops.

Materials Approved for Organic Production - Serenade has been shown to be effective against purple blotch.

Tomato hornworms. Photo by Eric Sideman.

Hornworms (Manduca quinquemaculata and Manduca sexta) - Hornworms are probably the most destructive insect attacking tomatoes and they are showing up now. They are giant caterpillars that can do a vast amount of eating in a very short time.

Right now we are finding young, tiny ones.

Sometimes it seems that overnight healthy looking tomato or pepper plants are striped of their leaves leaving bare stems. The hornworms will also attack the fruit eating gouges out so large that they look more like bites of a furry animal than an insect.

Look now for the damage and the frass, which is black pellets laying all around plants hosting hornworms. The frass may be your first sign there is a problem. The frass of young hornworms is small.

The adults are large, fast flying hawk moths, which, in flight, may look like a hummingbird. At dusk they hover over flowers sucking nectar. Eggs are laid on tomato leaves and hatch in 5 days.

Hand picking is a bit frightening but does work and chickens enjoy fighting with the challenging pest. The problem with hand picking is that they blend in very well and it is easy to overlook one or two caterpillars, which can do significant damage in a day or two. Bt works very well on this caterpillar.

Tomato hornworm with Braconid wasp cocoon. Photo by Eric Sideman.

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.)

MOFGA's Pest Alert - July 17, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Spotted Wing Drosophila. Photo by Martin Hauser, California Department of Food & Agriculture.

Spotted Wing Drosophila - The spotted wing drosophila (SWD) has been found in Maine. Only a few flies have been caught, but this may be just the beginning, and growers of soft fruits must be aware of the issue and make management decisions. See a detailed discussion, and a design of a trap that you can build to monitor the fly in your plantings.

This fruit fly is a new pest in our region. It is a very common pest in Asia. The tiny fly looks like a typical fruit fly, but the males have a spot on each wing that you can barely see with the naked eye. Common fruit flies that we see here only go after over ripe and rotting fruit. The SWD is a much greater problem because it can attack sound fruit and has been very damaging to raspberries, blueberries and many more fruits in areas south and west of us in recent years. Last year was the first year it was seen in large numbers in northern New England. It lays eggs in the fruit and in a few days, perhaps on your customer's counter, maggots will be wriggling.

The problem is that populations can explode quickly, and tolerance to maggots in the fruit is much less than let's say a corn earworm. I would say tolerance of maggots may be about zero.

At this time I do not have any tested recommendations other than common sense practices such as do not let ripe fruit sit on the vine or counter. Pesticides are quite effective if used timely. But the problem is timely is frequently. The generation time is so short that in order to control new arriving flies a grower may have to spray weekly or even more frequently. Alan Eaton, the entomologist at UNH, has put together some good fact sheets on potential efficacy of pesticides, including those used by organic growers. Check this out and look at the link to possible pesticides: http://extension.unh.edu/Agric/AGPMP/Spottedwingdrosphila.htm

Late Blight - Late blight has been found in a few more sites on potatoes in Maine. The newest one is Oxford County. It is still not widespread, a benefit of this hot, dry weather. Previous Pest Reports have had discussions of the problem, and for a detailed discussion see:


Above: Tarnished Plant Bug damage. Below: Tarnished Plant Bug. Photos by Eric Sideman.

Tarnished Plant Bug - Similar to the potato leafhopper, I often get calls from growers who believe they have a disease problem when actually it is feeding by the tarnished plant bug. This has been the worst year ever for us in Strafford, NH. But, I think it is local conditions that have led to that, not a regional problem. Our neighbor cut his hay field earlier than he usually does and that drove the bug out to find food. Our crops served well.

They are serious pests on strawberries (causing cat faced berries), lettuce (browning of midrib), flowers (destroying buds), eggplant and pepper (destroying buds and leaf tips), broccoli (brown beads in the head), and much more. But in potato they basically kill flowers (who cares?) and damage some of the leaflets (usually a minor problem). This year there are so many they are doing a lot of damage to potatoes.

The tarnished plant bug is a small (6 mm), bronze, brown and black bug that feeds on a very wide variety of plants, something like 300 species. They overwinter as adults under debris and become active in the spring. There are three or more generations per season. It is pretty easy to kill them with pyrethrum, but not worth it because their numbers are so great in all the fields of hay and weeds surrounding you that what you kill will be replaced in a day or two. Managing weeds and grassy fields so you keep the population low, e.g. mow short most of the time, but do not mow when you have sensitive crops, is about all you can do.

MOFGA's Pest Alert - July 5, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight Found In Maine

Late blight has popped up this week in Maine. I have received pictures from a farm in Woolwich, and it has been confirmed in the lab at the Pest Management Office, University of Maine Cooperative Extention. It is on both potatoes and tomatoes, although the confirmed sample was potato.

It was found earlier this week in Massachusetts. Quickly after, here. Rainy, humid, cloudy conditions provided favorable conditions for the pathogen to successfully be dispersed long distances and for infection to take place. Clouds protect spores being dispersed in wind from the killing effect of UV radiation. The spores are wimps and on a sunny day like today will die quickly in the wind.

All growers, including gardeners, should thoroughly inspect their potato and tomato plantings because this can be a very destructive disease when not managed, quickly killing foliage and rotting tomato fruit and potato tubers, AND be a source of spores spreading the disease to other growers.

Classic symptoms are large (at least nickel sized) olive green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid (early morning or after rain, or if it is dry you can induce it for identification by putting an infected leaf in a plastic bag over night). Sometimes the lesion border is yellow, but not usually. Often it has a water-soaked appearance. Leaf lesions begin as tiny, irregularly-shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit. There are great photographs at:


If you believe you have the disease, get a sample to your local Extension office, or send me a picture. Still, most of the suspects are proving to be early blight or Botrytis, so don’t jump to conclusions, but it is important to be vigilant.

If you find late blight in a localized spot in a field or garden, promptly destroy all symptomatic plants plus a border of surrounding plants to eliminate this source of inoculum. Physically pull, bag and get rid of affected plants. (This is done to prevent the spores from spreading to other farms.) Do not just drop in field as they will still be a source of spores. If disking is used to destroy a whole field, the crop should first be sprayed with fungicide because of the potential to move spores on equipment especially while driving out of the field, and the equipment should be pressure washed afterwards.

If you feel you have found late blight in only a localized spot, and most of your field is still clean of the disease, then you may want to spray a copper based fungicide. Copper products have proven to give good control, if sprayed before infection has occurred. DO NOT USE AT RATES OR FREQUENCY BEYOND LABEL INSTRUCTIONS.

[The legal Champ WP rate in the greenhouse is the same rate as in the field, that being 1 to 1.5 pounds (up to 4 pounds in severe cases) per acre for potatoes and 2 to 4 pounds per acre for tomatoes.

Greenhouse tomato coverage is about 1 ounce per square foot (the 1 ounce per square foot rate is equivalent to 340 gallons per acre in a field rate). Two level tablespoons of Champ WG per 1000 square feet of greenhouse is equivalent to 1 pound per acre. One level tablespoon of Champ WG per gallon of water is equivalent to 1 pound per 100 gallons.]

REMEMBER, only certain formulations of copper fungicides are allowed in organic production. Be sure to check with your certifier if you are not sure. Common formulations include Champion WG, Cueva Fungicide Concentrate, and COC WP.

Some of this information on management was provided by Dr. Steve Johnson, University of Maine Cooperative Extension, and Drs. Meg McGrath and Tom Zitter, Cornell University.

MOFGA's Pest Report - June 29, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

The season still is a tough one for many because of continued wet weather and wide fluctuations in temperature alternating from cool nights to heat waves. Growers with well drained soils are sure doing better than growers with clay or high water tables. Late blight is still popping up, but staying well south of us. I am worried because the weather has been right for it to spread north, but it hasn't yet. Keep your eyes open for a "Pest Alert" rather than the usual "Pest Report" in the subject lines of your emails from me. Spotted Wing Drosophila has been reported already, but it too is well south of us at this time.

In this issue of the Pest Report I will cover:

  • Asiatic Garden Beetle
  • Potato Leaf Hopper
  • Squash Vine Borer
  • Tomato Fruit Worm
  • Caterpillars in Brassica Crops

By the way, a week or two ago my brother was out walking and a farmer passing by in his truck stopped and rolled down the window and said, "your brother sure is a pessimist". I have that reputation in the MOFGA office too. Still, some find the Pest Report useful and stay happy. I am going to go out and enjoy this sunny day, the first in five.

Asiatic garden beetle. Photo by Eric Sideman.

Asiatic Garden Beetle (Maladera castanea) - I have received a few reports of activity of this critter. The Asiatic Garden Beetle is a native of Japan and China where it is not an important pest. The pest overwinters in the soil as a grub feeding on the roots in sod ground and weedy gardens. Some farmers are reporting problem with the grubs in their crop fields. The larvae (grubs) pupate early in the spring and the resulting adults emerge in June and start feeding on all sorts of garden vegetables. The adults are cinnamon-to reddish brown, rounded beetles. They eat big and irregular holes in the leaves and blossoms. You have to look hard to find them because they feed at night and burrow into the soil for the day. If you see chewed leaves and no pest, then go out at night with a flashlight and see who is there. It will probably be cutworms, or the Asiatic garden beetle.

If you have the problem, fall clean up with tilling the garden is important. Pesticides offer some control but often they are very numerous and seem to return from nowhere. Spinosad (Entrust and Montery Garden Spray) have been reported to work well.

Potato leafhopper damage. Photo by Eric Sideman.

Potato Leafhopper (Empoasca fabae) - I have seen some potato leaf hopper (PLH) already, so this is the time to keep an eye out for them. They could appear at your place at anytime, and remember, once you see severe damage from them it is too late to do anything. You have to find the insect and manage it before the plant symptoms catch your eyes.

They primarily feed on beans, potatoes, eggplants, strawberries and alfalfa. The PLH does not over winter anywhere near here. They over winter way down south and leapfrog up here in mass migrations. The first to arrive are females, and they are usually carrying fertilized eggs when they get here. Then there are a few generations over the growing season before the cold north winter kills them.

The damage from leafhopper is catastrophic. The bug sucks the juice out of the plant and injects a toxin that clogs the food conducting tissue. The symptoms look like a disease after a while, rather than insect damage, and is frequently mistaken as such. The leaves first get pale, then yellow and then brown from the edges. Then the plant dies. The symptoms are called hopper burn. It all happens very quickly.

The adult PLH is very light green and wedge shaped and tiny (an eighth of an inch long). The best way to find them is to brush the plant and watch one of the white-looking bugs land. The nymphs are similar to the adult, but have no wings and are even smaller and live on the underside of the leaves. If you disturb a nymph you will see it run and it can run sideways as fast as forward. This is a clue that you have PLH and not some other less harmful leafhopper.

The adults are flighty. When you brush your crop you will see them fly up. If there is a cloud of them, you are in trouble. Researchers have developed a threshold before treatment is recommended. Thresholds vary but here is one that is typical: Treat potatoes if 5 adults or 15 large larvae are found on 50 leaves.

Crop rotation does nothing for you since they are coming from far away. Covering your crops with a row cover would work, but these crops are not the type that are usually covered. Effective insecticides are limited. The only material that I have seen work that is allowed in organic production is pyrethrum, so Pyganic is the recommendation that I make. However, it does not work as well as a pyrethrum with PBO. BUT PBO is not permitted in organic production. If you market crops as organic, be sure to use an approved brand of pyrethrum, such as Pyganic 5%. Use the most concentrated mix allowed. Spray late in the day or evening, get good coverage including the undersides of the leaves, and don't wait until it is too late.

Squash vine borers. Photo by Jeff Hahn, University of Minnesota Cooperative Extension.

Squash Vine Borer - Squash vine borers are showing up in traps in NH already, and I am sure that southern Maine is next. Many vine crops are in bloom, and the row covers have been taken off to allow the bees access, and that means the borer now has access too. Care should be taken during bloom to avoid using insecticides when the bees are active.

Squash vine borer moths are day-flying moths with a 1.0 to 1.5 inch wingspan and bright orange markings. In flight, they look like wasps. There is one generation each year and adults emerge in late June/early July. The moths fly slowly in zig-zags around plants and lay eggs singly on stems; eggs are usually found on the main stem near the base, but are also found on leafstalks or on the undersides of leaves. Upon hatching, larvae bore into stems (where they are protected from insecticides). Thick-stemmed squashes are preferred. Unless you use traps or scout fields for evidence of eggs or larvae, the first sign of squash vine borer infestation is often wilting vines in July and August. By that time, it is too late to do anything.

Growers should scout their pumpkin and squash fields weekly for squash vine borer from late June through early August. Examine the base of vines for eggs. The squash vine borer can be killed with an insecticide and the recommendation would be spinosad (Entrust, Monterey Garden Spray), but appropriate timing is crucial. The insecticide is most effective when applied to young larvae before they bore into the stem. Once they are in the stem the insecticide will be useless. If you see the moths flying or find eggs, then two insecticide sprays, ideally applied to the base of the plants and timed five to seven days apart, will control newly hatching larvae before they are able to bore into the stem. Again, the timing is crucial and there is no point in spraying before you find evidence or after the larvae bore into the stem.

If evidence of larval feeding (sawdust-like frass near entrance holes) is found, then split open the stem to confirm the presence of larvae, which, by the way, may suggest more eggs are being laid so scout. Borers can be removed from vines if detected before much damage is done. Slit the stem longitudinally, remove the borer, then cover the wounded stem with moist soil above the point of injury to promote additional root formation.

Some growers monitor for the moths using Scentry Heliothis pheromone traps from early June through early August. If more than 5 moths per week are captured, then they make 2 to 4 weekly applications of pesticides. Timing is very important, so this is not recommended for the casual gardener. - Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA, UMass Vegetable Newsletter and URI Extension Fact Sheet.

Tomato fruitworm. Photo from North Carolina State University Cooperative Extension.

Tomato Fruitworm - I have seen in our own high tunnel of tomatoes, and have received reports from other growers, a caterpillar feeding on tomatoes. It is eating large holes in the side of the fruit. The numbers in each tunnel are small, but loosing even a single beautiful red tomato is awful. I think this is the tomato fruitworm, but it may be a related species. If anyone has a similar problem, please try to get me a sample. I took pictures, but my expert entomologist says he needs a specimen to get a sound identification. I put mine into the chicken pen and I cannot seem to find them anymore.

The tomato fruitworm is actually the same critter known as the corn earworm when it feeds on the tips of corn. It does not over winter here in the north, but every year, to a greater or lesser extent, they migrate up from southern regions. The preferred food is corn, but if none is available other items will do, e.g., tomatoes, peppers, lettuce, cotton and more. I rarely see them, except on corn.

The moth flies at night and typically lays eggs on the silk of corn. On tomatoes the eggs are laid on leaves near the flower or young fruit. The eggs hatch in 2-5 days. The caterpillar crawls down the silk channel to the kernels on corn, and to the fruit on tomato. They are pretty voracious feeders and can do a lot of damage. Rarely do you find two of them on the same fruit because they eat each other. The young caterpillar are pale, and the grown caterpillars are very variable in color, from green to brown to striped with spots. Bt will kill them, but I have not found enough to warrant spraying.

Above: Diamondback moth larva. Photo by Eric Sideman.
Above: Imported cabbageworm. Photo by Eric Sideman.
Above: Cabbage loopers at various stages. Photo from North Carolina State University Cooperative Extension.

Caterpillars in Brassica Crops - There are three common caterpillars that feed on our broccoli family crops. Keep an eye out for them. The imported cabbageworm butterflies are flying now.

Quick ID Cues:

  • Diamondback moth caterpillar: Green, very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons. They eat wholes in the leaves. There are many generations in a single season, even though they do not overwinter here.
  • Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow. They eat large chunks out of leaves. The adults are those white butterflies you commonly see flying around your broccoli.
  • Cabbage looper: light green, smooth, loops up like an inch worm as it moves. Eats big holes in leaves.

Scout undersides of leaves to look for fresh damage, and get control of the caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.

For organic growers both Bt and Spinosad are very effective (Bt products are a lot cheaper), but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying. Destroy crop after harvest so it does not act as a harbor for the pests all season.

For more information, contact:

Eric Sideman
Organic Crops Specialist
Maine Organic Farmers and Gardeners Association
Phone: 603-269-6201

MOFGA's Pest Report - June 7, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

This is the time of year that scouting is the most important pest management strategy on the farm or garden. This is when hibernating pests are waking from their winter nap and others are working their way north from warmer wintering grounds. Managing the pests now when they are in small numbers is more likely to be successful, and in some cases is the only way to save the crop.

In this issue:

  • Late Blight update
  • Garlic bloat nematodes
  • Cucumber beetles
  • Potato beetles
  • Squash bugs

Late Blight Update: There are more reports of late blight coming in from various places in NY and PA. It is very important to be scouting your fields now both for your own good and for the good of your neighbors. The weather we are having is very favorable for late blight to spread and we must do our best to catch it early.

If you need a refresher on how to identify late blight and manage it, see the following fact sheet: http://plantclinic.cornell.edu/factsheets/lateblight.pdf

Garlic infected with garlic bloat nematode. Note missing roots. Photo by Eric Sideman.

Garlic Buld Nematode (Ditylenchus dipsaci): The stem and bulb nematode, also called the garlic bloat nematode, is a new garlic pest in the Northeast, first appearing in New York in 2010 and now being found throughout the Northeast. It has been spread by infested garlic seed. I am now getting reports of growers finding it in their plantings. The microscopic worms feed by piercing root and leaf cells with their stylet. Leaves of severely infected plants turn yellow and dry prematurely. Plants may be stunted. The roots may be missing and the basal plate may appear to have a dry rot similar to Fusarium basal plate rot.

The pest is favored by wet, cool conditions. Although the pest is not active in hot dry weather, such weather may exacerbate symptoms. The nematode survives freezing and hot weather in soil and plant debris.

Most garlic naturally shows some yellowing of the tips of older leaves, so don't get worried right away. But, if you see some plants in your field that are significantly different than most with lots of yellowing and they seem stunted, pull them up and check the roots. If the roots are mostly missing, please get in touch with me and I will tell you where to send the sample for identification of this microscopic pest. DO NOT IGNORE THE PROBLEM, IT WILL GET WORSE. AND, MOST IMPORTANT, IF YOU SEE ANY DO NOT SELL ANY GARLIC SEED. THIS COULD BECOME A MAJOR PROBLEM AND WE DO NOT WANT THAT.

Cultural Control: The best way to avoid garlic bulb nematode is to use your own garlic for seed, IF it is not yet infested. Monitor for symptoms of infestation during the growing season and submit suspect plants to a diagnostic lab for confirmation. Contact the lab to get instructions how to take and where to send the sample.

If it is determined that you do have the problem, DO NOT use your own garlic for seed. Even bulbs that show no symptoms may have low levels of infestation. Obviously, do not sell any garlic for seed from a potentially infested lot. Do not replant garlic in an infested field for at least four years. Other hosts include all Alliums, celery, parsley, and salsify. Mustards, sorghum-sudan grass, and other bio-fumigant cover crops have been shown to reduce nematode populations in a field. These nematodes can survive in dry debris so carefully clean equipment and storage areas. There are no materials that offer control. (Reprinted from a draft of the soon to be published second edition of the Resource Guide to Organic Insect and Disease Management).

Cucumber beetles. Photo by Eric Sideman.

Striped Cucumber Beetle: (Modified from article in Mass. Veg. Notes written by Ruth Hazzard & Andrew Cavanagh). Striped cucumber beetle is showing up in south central Maine. Striped cucumber beetle is our most serious early-season pest in vine crops. These beetles spend the winter in plant debris in field edges, and with the onset of warm days and emergence of cucurbit crops, move rapidly into the field. Densities often are very high, especially in non-rotated fields or close to last year’s cucurbit crops. Management cannot wait because adult beetle feeding on seedlings (cotyledons and young leaves) is the most serious, and can cause stand reduction and delayed plant growth. Also, the striped cucumber beetle vectors Erwinia tracheiphila, the causal agent of bacterial wilt, and this may be more damaging than direct feeding injury. Crop rotation, transplants, and floating row cover are cultural controls that help reduce the impact of cucumber beetles. By far, floating row covers offer the best results. You must get the row cover on at transplanting or seeding. Early management is important to avoid early season infection with wilt. Cucurbit plants at the cotyledon and first 1-4 leaf stage are more susceptible to infection with bacterial wilt than older plants.

Perimeter trap cropping gives excellent control with dramatic reduction in pesticide use (see 2011 Pest Report for short article).

Beetle numbers should be kept low, especially before the 5-leaf stage. Scout frequently (at least twice per week for two weeks after crop emergence) and treat after beetles colonize the field. Early spot treatments of field edges can be helpful. The threshold depends on the crop. To prevent bacterial wilt in highly susceptible crops, we recommend that beetles should not be allowed to exceed one beetle for every 2 plants. Less wilt-susceptible crops (butternut, most pumpkins) will tolerate 1 or two beetles per plant without yield losses. Spray within 24 hours after the threshold is reached. Proper timing is key. The best approach is to avoid the beetles with a row cover or the use of Surround (see below for instructions on Surround), but if you missed the arrival of the beetles then pyrethrin should be sprayed very early in the morning, at dawn or before, to catch the beetles before they become active with the day’s warmth, and to give the pyrethrin time to work before the sun degrades it. Evening spraying can work for that, but often the beetles are flighty then and you see them flying up and away as you move down the row. Do not spray during the day when bees are active.

OMRI-listed insecticides available for use in striped cucumber management include kaolin clay (Surround WP), pyrethrin (Pyganic Crop Spray 5.0 EC), and spinosad (Entrust). In 2009 spray trials comparing these three products at the UMass Research Farm, kaolin was the most effective in reducing beetle numbers and feeding damage. There was a trend toward Surround WP being more effective when Pyganic or Entrust was mixed with it, but never significantly better than Surround alone. Other studies have shown more efficacy from pyrethrin and spinosad. Remember, Surround should be applied before beetles arrive because it acts as a repellent and protectant -- beetles do not “recognize” the plant and so do not feed -- not a contact poison. With direct-seeded crops, apply as soon as seedlings emerge if beetles are active. Transplants can be sprayed or dipped into the solution before setting out in the field.

I heard from a grower who tried out a vacuum and reported that it seemed to work well. He suggests using a vac with a low setting and/or a broad nozzle so that you don't damage plants. Also, do this earlier in the morning when they are sleepy and slow and be sure to look in their hiding places under the plants.

Three-lined potato beetles. Photo by Eric Sideman.

Cucumber beetles on my potatoes and tomatillo? No. Those are not cucumber beetles. Potatoes, tomatoes and sometimes eggplants are attacked by this pest that only superficially looks like a cucumber beetle. This is the Three-Lined Potato Beetle. The adult of this pest is about the same size as a cucumber beetle but has a reddish head and a thorax with two dark spots. The wing covers are dark yellow with three black stripes. Its favorite food in my experience is tomatillo.

The Three-Lined Potato Beetle overwinters as an adult and wakes early in the spring. They are there waiting for you to plant your solanaceous crops. The females soon begin laying eggs that hatch in about two weeks to larvae that look a bit like Colorado potato beetle larvae, except these critters have the endearing practice of carrying a small pile of their own excrement on their back. The larvae mature in about two weeks. There are probably two generations per year. On most crops the level of the pest does not warrant control. If this pest has been a problem in the past, floating row covers will help you avoid the overwintering adults and that should get you by. Hand picking will work on small plantings. Pyganic and Entrust may offer some relief. Rotenone works well, BUT REMEMBER THAT THERE ARE NO ROTENONE FORMULATIONS THAT MEET ORGANIC STANDARDS.

Colorado potato beetles. Photo by Eric Sideman.

Colorado Potato Beetle: (Leptinotarsa decemlineata). Colorado potato beetles (CPB) adults are just starting to show up in potato and eggplant crops. The bright yellow eggs will soon be laid in clumps with about 30-35 eggs each, generally on the undersides of leaves. As with most other insects and plants, there is a direct relationship between higher temperatures (in the range between about 55 and 90 degrees F) and faster rate of development. That includes egg-laying, egg hatch, larval growth, and feeding rates. A period of cold, rainy weather, like we have just had, slows everything down, but we can expect a surge of adults and shiny yellow eggs to appear with the next hot spell.

Scouting and Thresholds. Walk your fields soon and look for CPB adults and eggs. Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. Eggs hatch in 7-10 days, depending on temperature. If you want to know when the earliest eggs are hatching, you can flag a few of the earliest egg masses you find with bright tape or flags, and then keep an eye on the hatch.

Colorado potato beetle larvae - 4th instar. Photo by Eric Sideman.

Hatched larvae go through four stages before they become adults. In the first stage, the larvae are about the same size as the eggs and in the second stage they are about an eighth of an inch long. As the larvae get bigger, they do more feeding. The fourth, or largest, stage does 85% of the feeding damage. It’s a good idea to prevent beetles from ever reaching the fourth instar, but see below under timing control.

After larvae complete their growth, they drop to the ground and burrow into the ground to pupate. About ten days later the next generation of adults emerges – ready to feed. If they emerge before August 1, they will lay more eggs. After August 1, they feed and head to overwintering sites. Good control in June prevents problems with CPB in August. Potatoes can tolerate 20% defoliation without reduction in yield (or even more late in the season and cultivar). Damage to eggplant seedlings from adult feeding is often severe enough to warrant control of the adults. In potato, adult damage in rotated fields may not be significant, so usually you able to wait until after egg hatch to kill both adults and larvae.

Cultural Controls

  • Crop Rotation. The single most important tactic for CPB management is to rotate potatoes and eggplant to a field that is at least 200 yards from the previous year’s fields. Since the adult that comes out of winter cannot fly, 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 than non rotated fields. Also, the total population of adult beetles is lower, producing fewer larvae to control.
  • 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 if you are isolated and beetles from later generations in distant fields do not fly in.
  • Straw mulch. It has been well documented that when potato or eggplants are mulched with straw, fewer Colorado potato beetle adults will settle on the plants and fewer eggs will be laid. This can be accomplished on larger plantings by strip planting in a rye mulch, followed by mowing and pushing the rye straw over the plants after they emerge. For smaller plots, straw may be carried in.

Biological Control. There are numerous predators and parasitoids that attack CPB adults (a tachinid fly), larvae (12-spotted ladybeetle, spined soldier bug, ground beetles), and eggs.
Organic controls (OMRI listed products). Organic farmers face a particular challenge at this time because there is one very effective product, spinosad (Entrust), and other options (azadiactin, pyrethrin, and Beauvaria bassiana) are less effective. Consider trying these options anyway, to delay resistance to spinosad. Beauvaria bassiana (Mycotrol O) has been shown to suppress CPB populations over time, though it does not provide immediate control. Bt tenebrionis is no longer available. Cultural practices and natural biocontrols have become even more important in this situation.

Timing for Entrust. To get the most mileage out of the fewest applications of Entrust, time the first spray for when the earliest larvae are reaching the forth instar, or about half to 2/3 grown (see photo in web version of the Pest Report). This timing will catch the largest possible number of larvae while preventing significant feeding damage. (modified from the Umass Vegetable Notes, an article by - R Hazzard; (sources include: D Ferro (UMass Amherst), J. Mishanec (NYS), J Boucher (CT), J. Whalen (DE), T. Kuhar (VA), , G Ghidhu (NJ), New England Vegetable Management Guide, Ohio Vegetable Production Guide)

Potato Leafhopper Update: Potato leafhoppers are as far north as Massachusetts. Scout your potatoes, beans and strawberries. For details on description, life history, and management see the June 23, 2011 issue of the Pest Report.

 Squash bugs and eggs. Photo by Eric Sideman.

Squash Bug: Squash bugs are now being seen in southern Maine. Squash bugs (Anasis tristis) are serious pests of pumpkins and squash throughout North America. Damage and survival are low on watermelon, very low on cucumber and muskmelon, and highest on squash and pumpkin. Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Toxic saliva injected during feeding causes foliage to wilt, then turn black and die; the severity of this damage is directly related to density of squash bugs on each plant. Often I get calls by growers who believe they have a disease. Later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable.

Adults are 0.5 to 0.75 of an inch long, flattened and grayish-brown. They hibernate in trash in and around the garden for the winter and emerge in the early summer to feed a bit and lay eggs. Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch. The wingless nymphs are similar in appearance to adults, and are whitish when small, with a brown head, and grayish white when larger with black legs. There is one generation per year in the Northeast.

Black plastic, straw mulch, and reduced tillage systems encourage higher populations, probably by providing good hiding places.

Squash bug young nymphs and eggs. Photo by Eric Sideman.

Squash bug numbers are reduced by clean cultivation in the fall, and crop rotation. Infestation is delayed by row covers. If possible, rotate cucurbit crops between fields as far apart as possible. Keep headlands mowed and free of trash to reduce overwintering sites.

Squash bugs are unusually difficult to control with insecticides. Scout undersides of leaves for squash bug adults and eggs. Crush the eggs. You may not want to crush the bugs as they stink when you do.

If you miss some eggs and have to spray, time squash bug sprays to kill young nymphs just after hatch, because this stage is the easiest to control. Treat late in the day when the flowers are closed to reduce risk to bees. Neem products have proved effective.

For adult bug control, insecticides applied to the base of the plant are most effective, possibly because bugs tend to cluster. But, squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense. So now is the time to manage this pest.
(Source material from New England Vegetable Management Guide; Handbook of Vegetable Pests, A Capinera; ATTRA. Adapted by Andy Cavanagh & R Hazzard, UMass Extension, and modified for this Pest Report by me)

For more information, contact:
Eric Sideman
Organic Crops Specialist
Maine Organic Farmers and Gardeners Association
Phone: 603-269-6201

MOFGA's Pest Report - May 30, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight Detected In Long Island, NY
From Maine Potato Seed

Good morning MOFGA growers,

Yesterday we received notification from Meg McGrath (plant pathologist, Cornell University) that late blight was just identified in an early-planted potato field on Long Island. The farmer has destroyed the plants showing symptoms and has applied fungicides to protect the remainder of the plants.

According to Meg, the plants showed large brown classic late blight leaf spots; and a very few stems had large brown spots. She believes that the outbreak is due to contaminated seed. Two varieties with symptoms are Dark Red Norland and Superior; seed from Maine.

At this point, we are not concerned with spread of late blight from this initial site in Long Island. However, it is VERY important to scout your potato plantings for late blight symptoms, regardless of where seed was purchased. Also, now is the time to be scouting for volunteer potato plants from last year’s planting and destroying them.

Good resources with photos of symptoms and detailed discussions of how to manage late blight include:



If you suspect late blight, please take photos and send to me (esideman@mofga.org), or your county Extension educator. Any questions, please contact any me.


Eric Sideman
Crop Specialist
Maine Organic Farmers and Gardeners Association
Phone: 603 269 6201

MOFGA's Pest Report - May 25, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

This last weekend of May is often the big weekend for growers. It is time to free the seedlings from the confines of the humid greenhouses and tight cell trays. But remember to be smart and not make things worse by putting pampered seedlings into conditions that may be too wet, or too cold, or too dry, or too sunny or make them vulnerable to attack. Those decisions have to be made on a local basis. Although many calls I am getting now are problems arising from seedlings being trapped in containers too long in greenhouses that get too hot and dry surprisingly fast, and in most cases it could only get better by getting the plants out into the real world of fresh air and soil, it could get worse.

A common problem seen by folks trying to rush the season is wilting cucumbers. Even without being killed by freezing, cucumbers can suffer a great deal and perhaps die from being in cold conditions. The small roots and root hairs of cucumber and other cucurbits give out in the cold. It may look like it is a sudden wilting of the plant due to drought, but really the problem comes on from the cold soil and then when there is a bit of sun or warmth and the plants need water they cannot get it, even if the soil has plenty to offer. Some parts of New England still have cold soil, although most places are plenty warm.

If you have delayed onion planting because things have not been right yet, or are replanting because the maggots got all the onions you put out earlier, then sunscald can be a problem. This is a problem that results from sudden hot weather. On hot sunny days the temperature at the soil surface gets very hot. The heat can damage sensitive young onion seedlings that are either just germinating or just set out as transplants. The injured tissue shrivels, strangling the neck right at the soil line, and the plant wilts and withers. The only way to avoid sunscald is to plant seed earlier in the spring so that the plants are beyond the sensitive stage before the soil temperature becomes too hot, or be lucky and not get hot sunny days when the tiny seedlings are sensitive.

The grubs that are the common problems in New England are the larvae of a bunch of beetles that may be a problem later in the year, such as the Japanese beetle, the Asiatic garden beetle, or the June beetle. The grubs live happily under sod and unless the populations are enormous, you may not even know they are there. Sod has lots of roots. But if you make a garden in an area that was lawn or some other sod, the grub population is the same size and the amount of root is much less. Quickly the grubs zero in on the crop and eat all the roots.

These species of beetles have similar life cycles but they do vary in number of years spent as a grub. The grub is causing the problems now for many new growers, or growers opening new fields. Later in the season I will get calls about the adults. Typically adults emerge from the soil in early summer to feed and mate. The females burrow into the soil (often in or near wide expanses of grass or sod) to lay eggs, usually beginning in late July and August. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads). In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding. I am getting calls now about wilting plants that have few roots left.

There are not many controls for organic growers to choose from after the grub problem is discovered. Beneficial nematodes work fairly well on the grubs if there before the population explodes. The more technical term for these tiny round worms is entomopathogenic nematodes, and they have shown good efficacy when environmental conditions are favorable. Success with nematodes depends on proper application methods. Be sure to follow the instructions from the supplier carefully. 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).

(Reprinted from the UMass Vegetable Notes)
The first flight of European Corn Borer (ECB) has begun in warmer parts of the Connecticut Valley, in the plateaus near the river. Many thanks to the alert grower in Hatfield, MA who got his traps up and started catching moths! This is considerably earlier than the average emergence date for ECB. European Corn Borer overwinters as a late instar larva in the stalk of corn and other host plants. Its development into a pupa and then emergence as an adult moth is temperature-driven. The average degree day accumulations are almost double what they were at this time last year for many parts of the state, which is driving the early emergence.

Even if your corn is small, any farmers who are using traps to monitor flight should put them up as soon as possible to be able to tell if flight has begun in your area. Corn is still small, and most of the corn grown under clear plastic has yet to be cut out. If the predicted high temperatures of the coming weekend come to pass plastic corn will need to be cut free of high heat under the plastic. Once exposed, this larger corn is likely to attract egg-laying females ECB moths. Managing ECB in early corn, whether grown on bare ground or pushed ahead by plastic or row cover, can be tricky. Usually we wait until pre-tassel and scout for feeding damage and small caterpillars in the emerging tassel. When corn is in whorl stage as flight begins, eggs are laid earlier in the corn's development and there can be feeding at the whorl stage. ECB feeding in the whorl can be detected as pinhole leaf damage in the inner part of the whorl. When this happens large ECB larvae may still be around when ears form and their damage can slip by because it does not show up in the tassel.

There is no need for alarm; no one needs to rush out and start spraying corn. However it's worth paying attention and scouting closely for both flight and feeding damage on that valuable earliest corn. It has been found that when when ECB flight starts early and corn is infested in the whorl stage, a late-whorl spray can prevent ear damage in these early plantings.

We are still 1-2 weeks (depending on our GDD accumulation in the next week) from active feeding even in the warmer parts of the state where flight has started. In cooler parts of the state, flight will likely begin within the next 7-10 days. We know that more growers are using Trichogramma ostriniae, the tiny wasp that lays its eggs in ECB eggs. Timing is key for effectiveness: once eggs are hatched it’s too late! Any growers using Trichogramma ostriniae for control should be planning to release soon. The ideal time to release T. ostriniae is when eggs are in the field, but before eggs hatch. To be conservative, we prefer to release the same week that flight begins as the additional GDD for egg laying will very likely accumulate within that week. See charts below for degree days. Degree day information for many locations in MA can be obtained through the NEWA website ( http://newa.cornell.edu/). Note that the base temperature for ECB is 50 degrees Fahrenheit (10C). More information on using T. ostriniae can be found in our April 24 issue of Vegetable Notes, available at http://extension.umass.edu/vegetable/publications/vegetable-notes-newsletter/archives.

ECB first generation development
GDD (base 50F)
emergence 375
first eggs 450
egg hatch 550

MOFGA's Pest Report - May 15, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Spring Woes: This is a very good year to point out the importance of consideration of soil type when buying your farm or garden. I often say you can deal with anything, and dealing is what is happening now for those of us who did not think about it much back then and now have poorly drained soil. Two related problems that I discussed in the last issue of the Pest Report are very common this year. I have never had as many calls about onion maggot and seed corn maggot as I received last week, and spinach germination and survival is at an all time low. Spinach is going down (or not coming up) due to damping off and/or the seed corn maggot. See last week's issue for details. If waiting for dry, warm soil seems futile, you may want to spend some money on products. There have been some fair-good reports of successful avoidance of damping off using a biological control product made from Trichoderma, such as, RootShield® Granules or RootShield® Home & GardenBiological Fungicide (BioWorks, Inc.), and SoilGard® 12 G Microbial Fungicide (Certis). Let's hope for some dry weather as that would be best.

Above - Adult common asparagus beetles.
Above - Asparagus beetle eggs.
Above - Asparagus beetle larvae.


Frost - One of the very first questions I received when I began working for MOFGA many, many years ago turned into an argument. Not a good start for my tenure, but I stuck it out. The guy who called would not believe me that asparagus is frost sensitive. His spears had turned dark, wrinkled and water-soaked and I don't know if I ever convinced him. Perhaps he is reading this. Asparagus, despite its status as a primo early season vegetable, is highly sensitive to frost, ranking alongside cucumber, snap beans, eggplant and tomatoes in the ‘most susceptible’ category. The early hot spell this year moved everything, including asparagus, ahead by weeks. It made some growers in-the-know uneasy as spears pushed out of the ground, only to face the a string of cold nights. There is still a good chance of frost though you would not believe it since it was over 80 yesterday! When frosted, spears appear slightly darker green, water-soaked and break off easily. Thawed spears become mushy. Soft-rotting bacteria can enter the damaged tissue. New spears take several more days to emerge, but will. Temperatures below 33 degrees Fahrenheit may damage the spears.

Beetles - Common asparagus beetles are here. The spotted asparagus beetle generally becomes active somewhat later in the spring, and in my experience is less common (I guess with the names that is not a surprise). These two beetles are closely related and have similar life cycles, but it is the common asparagus beetle that is most damaging to the spears.

  • Common asparagus beetle (Crioceris asparigi) is blue-black, shiny, smooth and about 6 to 9 mm (1/4 inch) long, with three large yellow, squarish spots with red margins along each wing cover. Eggs are black, laid standing on end in rows along the spears, and hatch in 3-8 days. Larvae are wrinkled, plump, hump-backed, and dull gray with black head and legs. Some people call them "worms". They grow up to 1/3 inch. These larvae feed in spears and in ferns. The larvae do the most damage, and eggs and larval damage makes spears unmarketable. Larval feeding can cause severe defoliation and weaken the stand. When full grown, larvae drop to the soil and pupate underground. New adults emerge in July, feed in ferns, and by September are looking for overwintering sites. Both species spend the winter as adult beetles either in field borders or within the asparagus field. Sheltered sites such as under bark or in the stems of old plants are preferred. Some burrow into the soil.
  • Spotted asparagus beetle (Crioceris duodecimpunctata) is reddish orange or tan, with six black spots on each wing cover (hence its other name, 12-spotted asparagus beetle). Eggs are greenish, glued singly on their sides to leaves. Eggs are laid on fronds, not on spears. Larvae are similar to those described above, but are orange colored, and feed almost entirely inside the berries so they affect seed production but do not hurt the plants.

Cultural controls: During harvest, you can greatly reduce the population by harvesting ALL of the spears every harvest. Pick the field clean to reduce the number of stems where eggs will survive long enough to hatch or larvae can feed and grow up into summer-generation beetles. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter, by disking lightly (avoid crown damage) or burning crop stalks and fronds. Maintaining a clean environment in the fall will force beetles to seek shelter outside the field or burrow in the soil, where many predators reside.

Biocontrol: The most important natural enemy of Common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. Wasps kill eggs by feeding on them (sucking them dry), and also lay their own eggs inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs killed by feeding and half of the surviving larvae parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.

Monitoring and chemical control: Scout fields regularly. You may want to treat spears if >10% of the plants are infested with beetles or 2% have eggs or damage. The daily harvest makes treatment difficult because few want to spray anything close to harvest time. Treating infested fronds is important. Organic options include Entrust. Surround WP may work as a repellent. Thanks to for information: -R. Hazzard (U. Mass Vegetable Notes & The New England Vegetable Management Guide), and Brian Caldwell, Cornell University.

Above - Adult Mexican bean beetle.
Above - Mexican bean beetle larva.

Mexican Bean Beetle: Plan Ahead For Biological Control (Reprinted and modified from Mass. Veg. Notes, written by Ruth Hazzard and A. Brown)

If Mexican bean beetles have historically been a problem on your farm, you will very likely see them again this year. They may be pests on snap beans, soybeans, and lima beans. While they are not a pest on every farm, some farms report repeated significant damage from these pests and have to take action to prevent crop loss. Using biological control can reduce the need for insecticides.

Mexican bean beetle (MBB) adults are coppery brown with black spots. They look very much like large ladybeetles and in fact are closely related – but unlike lady beetles they feed on leaves, not other insects. Adults lay yellow-orange egg masses on the underside of bean leaves. These hatch into bright yellow, spiny oval larvae, which feed, molt several times as they grow, and pupate on the underside of leaves. Feeding damage from adults and larvae can reduce yield and injure pods if numbers are high. There are several generations per season, often with increasing populations in each generation.

Pediobius foveolatus is a commercially available biological control agent for Mexican bean beetle control and has a good track record in the mid-Atlantic states and among New England growers who have tried it. (Pediobius is pronounced “pee-dee-OH-bee-us”). It is mass-reared and sold by the New Jersey Dept of Agriculture and is also available from other beneficial insect suppliers. This small (1-3 mm), non-stinging parasitic wasp lays its eggs in Mexican bean beetle larvae. Wasp larvae feed inside the MBB larva, kill it, and pupate inside it, forming a brownish case or ‘mummy’. About twenty five adult wasps emerge from one mummy. Control continues and in fact gets better as the season progresses and successive generations of the wasp emerge and search out new bean beetle larvae.

Planning 2-3 releases at 7-10 day intervals will help ensure good timing and coverage on several plantings. This makes it well suited to our succession-planted snap bean crops. After a release in the first plants, it is advisable to leave that planting intact for a while, until the new generation of wasps has emerged from their mummies. As with any biological control, make releases as soon as the pest is present – not after it has built up to damaging numbers. The New Jersey Dept of Agriculture Beneficial Insect Rearing Laboratory recommends two releases, two weeks in a row, coinciding with the beginning of Mexican bean beetle egg hatch.

Wasps will lay their eggs in larvae of any size, but it is best to target the newly-hatched young MBB larvae. This will give control before damage has been done. Thus, timing is important. Watch for eggs and time the shipment for the first hatch of eggs into larvae. If in doubt about the timing of the hatch, release as soon as you see the eggs – if you wait for the larvae you may be playing catch-up. The release rate should be at least 2000 adult wasps per field for less than an acre, or 3,000 per acre for fields of one acre or more.

The 2009 cost from NJDA is $40 plus shipping for 1000 adults, or $20 for 20 mummies (pupal parasites inside dead MBB larvae) from which about 500 adults will emerge. Order adults if you already have MBB larvae in the field. Ship for overnight delivery. Instructions for handling and release will come with the wasps. Wasps reproduce in the field and will still be around when the second generation of MBB hatches out. Thus, it should not be necessary to make more than two releases. Like beans, Pediobius wasps are killed by frost.

Plan ahead by contacting a supplier to inform them of your expected release dates and acreage. Contact information for New Jersey source: Tom Dorsey, 609-530-4192; address; NJDA, Phillip Alampi Insect Lab, State Police Drive, W. Tren- ton, NJ 08628. http://nj.gov/agriculture/divisions/pi/prog/beneficialinsect.html. You’ll also get advice on how to use the wasps from this office. Pediobius is also available from the following suppliers: Green Spot Ltd., NH., www.green-methods.com 603-942-8925; IPM Laboratories, NY 315-497-2063; ARBICO, 800 -827-2847 (AZ), http://www.arbico.com/; Network (TN), 615-370-4301, http://www.biconet.com/.

If you would like assistance in using these biocontrols in your bean crops please call the UMass Extension Vegetable Pro- gram at 413-577-3976 or 413-545-3696 or email at

Materials Approved for Organic Production: Moderate control can be achieved with Entrust as well as mixtures of pyrethrin (Pyganic EC5.0) and Neemix.

Above - Late blight in tubers.
Above - Fusarium dry rot.
Above - Ring rot.
 Above - Black scurf.

Potato Planting Time: Don't Plant A Problem

Potato seed tubers are often the source of infection for your crop and inspection before planting is well worth the time. Some problem seed pieces are not going to spread a disease and can be planted. Others should never be planted. Here are some common issues:

  • Late Blight - Of course this is the big one. Look at the picture on the web version if you don't know what this looks like. If you are not sure, check with an expert. Besides taking down your potato crop, this is the most likely source of a community or state wide problem this year. Do not plant any potatoes suspected of being infected with late blight.
  • Fusarium Dry Rot - This is probably the greatest cause of loss in storage. It is also seen on seed pieces, and can result to seed piece decay after planting and result in uneven stands. A slimy rot often develops when Fusarium dry rotted potato seed is planted. This is a secondary infection by bacteria, which take over. Do not plant seed pieces with Fusarium dry rot.
  • Ring Rot - This is one of the worst diseases you can get on your farm because once you get it is very hard to get the farm clean again, and it spreads very easily by the bacteria clinging to boots, crates, and equipment. Check your seed carefully and discard the whole load if any ring rot is found. In the tuber you will see the disease as a break down of the ring of vascular tissue when you cut the potato. Squeezing the tuber will expel creamy, odorless ooze of bacteria. Planting these tubers will introduce the bacteria to your soil.
  • Scab - Lesions on the tuber are usually circular and seldom larger than a half inch, but in very bad infections they coalesce. They may be a cork like layer or pitted. The layer under the lesion is straw colored. Planting these tubers will introduce the bacteria to your soil.
  • Black Scurf - If you have little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, then you have black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani. The black specks are one of the ways the fungus reproduces. They are called sclerotia, which are tight, dry masses of fungal tissue (mycelium) in a resting phase. In the spring the sclerotia germinate and infection of the new potatoes begins. Most commonly, infection of potatoes is from planting potato seed pieces with sclerotia on them. Crop rotation is not very effective because sclerotia can survive for many years without a host crop. So, avoid ever planting seed with the disease.
  • Hollow Heart - Just as the name implies, the center of the potato is hollow. It appears as splitting with the tuber and the inner walls may be white, tan or even may be rarely infected with a secondary disease. Hollow heart is not caused by a pathogen but rather by rapid tuber enlargement especially after a period of moisture stress. Potato seed with hollow heart will not spread the disease.
  • Knobby potatoes - Potatoes with knobs are usually the result of high field temperature and drought or other conditions that cause irregular rates of tuber development. Planting knobby potato seed will not spread the problem.

Flea Beetles In Brassicas:

I have had no reports of flea beetle feeding yet, but I bet that feeding on early spring plantings of brassica crops will start soon. Then numbers are likely to rise quickly as beetles move out of field borders where they spent the winter. Since row covers are by far the best management strategy, it is better to be prepared than wish you were.

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. This is good to know when planning rotations.] 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. The crop quickly becomes unmarketable. In contrast, waxy crops are most susceptible at the cotyledon and seedling stage, and then feeding is more limited to leaf margins on older plants. Usually the crop outgrows the pest so use of row covers is usually not essential on the waxy crops. 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 or 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 early in the spring.

 Flea beetle trying to get through Proteknet.

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, plastic bags filled with soil, or some other method.

This may be the year to try out the new product called Proteknet. It is distributed by Dubois Agrinovation, out of Canada.


Fedco is selling it this year in smaller rolls. It is, as the name implies, a fine net rather than a spunbound covering. It is said to have a 5-year or more life. [See the web version of this Pest Report for a picture.]

Spinosad (Entrust is organic formulation) is proving to be effective in suppressing flea beetles and reducing damage. Pyrethrum (Pyganic EC 5) showed poor to moderate efficacy in trials, and has a short residual period. But, 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. (Thanks to the UMass Vegetable Notes for much of the information above).

MOFGA's Pest Report - May 1, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Introduction to the Pest Report

The Pest Report is produced once every week or two during the growing season. It is a compilation of short discussions of pests and diseases either working the fields or soon to be seen. Some of the pieces I write myself, some of them I pick up with permission from other crop advisors around New England. Often I learn about an approaching problem from folks in southern New England states where problem often arise first, and so I pass on the warning. I have been writing the Pest Report for many years and there is not much new now, so many of the articles may seem familiar because I have simply updated a report from the past. I email the report to all of the MOFGA certified farmers, and other growers who have requested it.

This is the first Pest Report of the spring of 2012, and what a spring it has been. The effect of the early season of temperatures way above normal is still being felt even though we have had record low temperatures recently. And, the effects are not good for fruit growers whose very advanced buds are susceptible to the frosty and freezing nights. For a discussion of frost and fruits, with a great table that notes the critical temperatures for damage to fruit buds, see http://extension.unh.edu/Agri/Docs/FVApril2012.pdf.

Vegetable growers got off to a great early start with warm, dry soils, but now cold and wet weather has set in and I feel like mother nature is saying "I fooled you". Some of us may be hurt by jumping the gun. I will concentrate this first Pest Report on those pests that are out there enjoying the cold, wet weather.

SEEDCORN MAGGOTS Hylemya platura

Now is the time to be aware of the problem. Seedcorn maggot larvae feed on seeds and young seedlings of many crops (corn, beans, beets, peas, spinach, cole crops, etc.). The first symptoms are usually poor germination (or failure of seedlings to emerge), or wilting plants that have lost their roots to feeding. Symptoms can be difficult to distinguish from other problems, like damping off due to Pythium or other soilborne fungi, or wireworm feeding. If seedcorn maggots are the culprit, maggots can usually be found in the soil around and inside seedlings and seeds. The seedcorn maggot is yellow-white, 1/4 inch long, legless, with a wedge-shaped head. The adults look like small houseflies. Seedcorn maggots overwinter in the soil as pupae. In early spring, the adults emerge and lay eggs, which hatch within 2-4 days at soil temperatures of 50F. Research has shown that peak emergence of the first three generations occur when 200, 600 and 1000 degree days have accumulated. Degree days are calculated on a daily basis by using the formula: (Max temp – Min temp)/2 – 39F. You can also refer to a handy calculator at http://www.weather.com/outlook/agriculture/growing-degree-days.

The first generation usually causes the most damage. The adults prefer to lay eggs in wet soil that is rich in organic matter. Crop seeds that germinate slowly are more vulnerable to attack. The adults are active ahead of schedule this year, and crops that are planted in wet soil when the soil is too cool for them to germinate quickly may be especially susceptible to damage. I just had some spinach seedlings wilt and when I pulled one up it was swarming with maggots.

Management strategies:

By the time you see damage, it is too late to control the problem using either cultural or chemical methods. Prevention is the key.

  • Avoid seeding fields (especially wet fields) too early. Seeds germinate more quickly and are less vulnerable in warmer soils.
  • Disk and incorporate organic matter (such as a cover crop) at least 4 weeks before seeding to give it time to break down and make it less attractive to the flies.
  • Avoid applying manure or unfinished compost in late fall or early spring to heavy soils that you might want to plant early. Lighter, well-drained, sandy soils are less likely to have problems (because they warm up faster than others).
  • Rowcovers can help – but only if the maggot flies are coming from elsewhere. Damage can occur if the flies have overwintered in the soil and thus end up underneath the rowcovers.
  • If you need to replant, wait at least 5 days if maggots that you find are a quarter inch long; if they are smaller than that, wait at least 10 days to make sure they have pupated and will not damage the new seeds.


Spinach seedling with tiny white maggots feeding on the roots. Photo by Eric Sideman.


Raising seedlings in a "sterile" mix such as Pro Mix is easy. These mixes are called sterile, however they are not really sterile. On the other hand they are called sterile by growers because they don't have plant pathogens in them, and that beats my home-made mix. These "sterile" mixes are mixes of pathogen free materials such as peat, perlite, vermiculite with synthetic and very available sources of plant nutrients added in just the right amount to get newly germinated plants off and growing. Organic growers do not have the option to use these mixes. We either purchase mixes that are generally based on compost, or mix up our own. Seedling problems are much more likely in organic mixes because of the possibility that the compost may be carrying plant pathogens. In addition, it is much more difficult to predict the availability of nutrients from natural sources because of how it depends on biological activity, which is greatly affected by temperature, moisture and other factors. Many commercially available organic mixes are quite good and consistently free of pathogens, and good with nutrients, but occasionally even these fail. Home made mixes, such as the one I make, fail more regularly. Here are some of the problems I have seen frequently in my home made mix, and occasionally in commercial mixes.


Damping-off is a disease most commonly seen in young seedling but may rarely effect older seedlings. It is caused by species of fungi that commonly live in the upper layers of soil and when things are not right these pathogens jump at the opportunity to infect germinating seeds and seedlings. The two most common species that cause damping off are in the genera Pythium and Rhizoctonia.

There are two types of damping off. The first is one growers often misinterpret because it is pre-emergence damping-off, which rots the sprouting seed before it breaks through the soil. Growers often blame the seed companies for poor seed. The fungus attacks any part of the germinating seed especially the tiny growing tip. Post-emergence damping-off begins as a lesion on the root which extends up the stem to and/or above the soil line. The young stem is constricted by the attack and becomes soft, and the plant falls over and dies.

Damping off cannot be cured but it can be prevented by starting seeds in better conditions (or the "sterile" media). First make sure you are using seeds of the highest quality. Old, mistreated, and weak seeds are more susceptible to damping-off. Anything that slows germination increases the risk of infection. Excessive watering, poor drainage and less then optimum temperatures should be avoided. Allow the surface of the container to dry a bit before watering.

It is possible to "sterilize" your media by baking the mix in the oven at 3500 F for about 45 minutes. The mix should reach 1600 and should stay at that temperature for 30 minutes. Do not allow it to go higher or stay hot longer because overheating kills the beneficial microorganisms and may releases toxic materials.


Seedling suffering from damping off. Photo by Eric Sideman.

Cold Soil/Wet Soil

In addition to damping off, cold soil can cause other problems. Growing seedlings on window sills is often a problem because of cold night time temperatures. The roots of plants do not function when cold and plants frequently display symptoms of malnutrition even thought the media may have plenty in it. Purple undersides of leaves, stunted growth, pale weak seedlings are often the results of cold feet or wet feet. Trying to grow a tiny seedling in a large container may have the same effect because the plant is just not big enough to use the water, and over watering may be a problem the plant cannot get out of.


Some composts are high in soluble salts. Even if the salts are nutrient salts such as nitrates, high salts will cause water absorption problems and may prevent seeds from germinating. Salty composts are not a problem in field use because they become diluted with the soil, but in a seedling media it is a real problem. Compost used for media should be the best you can get and should not have salts -measured as conductivity on a compost analysis- higher than 1mmhos.


The C:N ratio is critical for compost used in potting mixes. A high C:N ratio will result in nitrogen lock up, which is a case where all the nitrogen in the media, and any you add with fertilizers, is being grabbed by the bacteria feeding on the carbonaceous material. It is a sign that the compost was made from an improper mix of feedstock, or perhaps is just not finished yet. Compost used to make media should have a C:N ratio of 15:1 to 18:1.


As nitrogen is released from decomposing proteins in a compost pile it passes through a phase where it is an ammonium ion. Unfinished compost will have ammonium ions that may revert to ammonia and kill roots. Ammonia nitrogen in a compost used for a potting soil should be less than 0.1%. Problems from high ammonia can be seen as very weak, dying seedlings, and when you pull them up you see that the roots are brown instead of a nice healthy white.

My recommendation is to get an analysis of any compost you plan to use to build your own seedling mix. The University of Maine Soil Testing Laboratory does compost testing. Just be sure if you send a sample to ask for the compost analysis. If you are buying a commercial compost based mix you may want to speak to other growers and see how that brand has worked for them.



Above I discussed damping-off of seedlings. Last year I received calls about peas dying just after or just before germinating and I thought I better say that damping off can occur in the field too. This time of year the problem is with peas.

The disease is caused by several different species of Pythium, which is a common soil inhabitant that persists in soil in root debris as spores. The species have a wide host range of crops and weeds and so crop rotation will do little to avoid the problem.

During or just after germination the pea seedling begins to show symptoms. The symptoms may be as simple as yellowing and stunting because sometimes only the root tips are infected and this root pruning interrupts growth. Sometimes a soft rot of the stem kills the plant. Sometimes you just don't see any pea germinate.

High soil moisture and warm soil temperatures (warmer than optimum for pea growth, i.e., 65-75) favors Pythium. You can't control the weather but you can choose when you plant your peas. If the soil is very wet and warm weather is forecast it may make sense to delay planting a few days for the soil to dry a bit.

There are resistant varieties. The resistant gene is tied to some visual characteristics of the seed. Wrinkled seeds are more severely affected than round seeds. Also, some biological seed treatments such as Rootshield may help.

Home | Programs | Agricultural Services | The Fair | Certification | Events | Publications | Resources | Store | Support MOFGA | Contact | MOFGA.net | Search
  Copyright © 2018 Maine Organic Farmers and Gardeners Association   Terms Of Use  Privacy Statement    Site by Planet Maine