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 MOFGA's 2011 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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MOFGA's Pest Report - August 4, 2011
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist

Late Blight Update: Late blight has been found this week in a garden in Vermont. It still remains only in a small number of isolated spots around the Northeast (one in the County in Maine, a garden in Vermont, a few farms in New York on Long Island, etc.). It is not time for tears or fear yet, BUT it is time for vigilance. Be sure to scout your potatoes and tomatoes frequently. If you find a problem and suspect late blight, please send me a picture (in focus please). If I suspect late blight, but it is not a clear case, then I will suggest you send a sample to the Pest Management Office for positive identification. At this time, none of the many pictures I have received have been late blight. At this time, early blight and septoria leaf spot are common, and in some damp situations Botrytis is popping up. Here is a great site with good pictures:


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. 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 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, especially when they are small.

Tomato hornworm with Braconid wasp cocoons. Photo by Eric Sideman.
What Are Those White Things On The 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)

Powdery Mildew (Podosphaera xanthii): Powdery mildew is a common disease of pumpkins and winter squash. All cucurbits are susceptible, but many common cucumber and melon varieties are resistant. The disease can cause infected leaves to die prematurely, reducing yields and lowering fruit quality, especially taste. Winter squash from diseased plants won’t store as long as fruits from healthy plants, nor will it be as sweet because late season sugar production is important to squash quality and with no leaves there is no sugar production.

First spots of powdery mildew. Photo by Eric Sideman.
The fungus that causes the disease does not overwinter in Maine. Spores blow up every year from southern overwintering sites. If they arrive late in the season, you may not need any control; but if they arrive in early to midsummer, exercise some control or you may have no leaves by mid-August.

Powdery mildew reports are now coming in to me. This may warrant attention. Go out and scout.

Check upper and lower surfaces of leaves of older plants every few days starting now. The first symptoms usually are white, powdery fungal patches on the undersides of older leaves. Yellow spots may form opposite these, on the upper leaf surfaces.

No products with systemic activity (products that move through the plant) are approved for organic production, and applying fungicide to the lower leaf surface is difficult. In experiments, foliar applications of sulfur have been more effective than most other organic products for powdery mildew, apparently because sulfur deposited on the upper leaf surface can volatilize and be redistributed to the lower surface. Sulfur can be phytotoxic on melons, especially if applied when temperatures are hot.

ATTRA (National Sustainable Agriculture Information Service, www.attra.ncat.org) reports that a single spray application (to runoff) of 0.5 percent (wt./vol. of water) baking soda, plus 0.5 percent (vol./vol. of water) SunSpray UFP® horticultural oil almost completely inhibited powdery mildew on heavily infected pumpkin foliage; while baking soda without the oil was ineffective, and a 2 percent (wt./vol. of water) solution of baking soda damaged the leaves. But, remember if you are a commercial grower then you should be using EPA registered pesticides and not homemade concoctions.

Mexican Bean Beetle Larva. Photo by Eric Sideman.
Mexican Bean Beetle (Epilachna varivestis):
The Mexican bean beetle is one of the few members of the lady beetle family that has evolved to feed on plants rather than be a predator of other insects. It is a somewhat spotty pest in the Northeast with many farms never seeing one and others having crops devoured year after year. This year I have received a few reports already. This beetle feeds on snap and dry beans primarily, and may be seen feeding on soybeans or cowpeas sometimes. The larvae skeletonize leaves turning them into lace. The adults feed on leaves and pods too. The adult looks like a lady beetle with 8 black spots arranged in rows across the body that may range in color from rust to yellow. The larvae are very spiny, slow moving critters that are bright yellow.

The Mexican bean beetle spends the winter as an adult hiding in trashy and weedy areas along the edges of fields. They move into fields in the late spring to early summer and feed for about a week or two before the females lay groups of orange eggs on the underside of leaves. These hatch in a week or two and the larvae will feed for about three weeks. The reports I am getting now are larva, which, I guess, are weird enough to prompt a call to me. The larvae pupate and a new generation of adults emerge in about 10 days. The worst damage from this pest occurs in late July and August. Near New York City there are two generations per season while in the north there is only one.

Moderate control can be achieved with Entrust as well as mixtures of pyrethrin (PyGanic EC5.0) and Neemix.

For next year, discourage hibernating beetles by cleaning up all plant debris after harvest. Maintain wide, clean headlands and brushless wood edges. Plow under crop debris shortly after harvest.

Biological control is proving very effective. Pediobius foveolatus is a wasp that lays its eggs in the larva. The wasp larvae feed inside the MBB larva and eventually kill it. About 25 new wasps emerge from each killed MBB larva and so control actually gets better as the season progresses. Plan on making the release of the wasp as soon as the pest is present, not before nor after it has built up to damaging numbers. It is recommended to make two releases two weeks in a row. It is too late for this year, but if you have it, be prepared for next year to see it again.

Pediobius is available from the following suppliers: New Jersey Department of Agriculture (contact Tom Dorsey at 609 530 4192; http://nj.gov/agriculture/divisions/pi/prog/beneficialinsect.html

Green Spot Ltd., NH, (
603-942-8925, http://www.greenmethods.com)
IPM Laboratories, NY, (315-497-2063)
ARBICO (800-827-2847, http://www.arbico.com/)

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