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 MOFGA's 2010 Pest Reports - Compiled by Eric Sideman, PhD Minimize

September 22 | August 23 | August 9 | July 26 | July 20 - Late Blight Update | July 19 - Late Blight Is Here | July 7 | June 24 | June 19 - Late Blight Update | June 18 | June 8 | May 25 | May 20 | May 3 | April 22
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Pest Report - August 9, 2010


Late blight is still being reported only in a handful of sites in Maine, in gardens and a few market farms. At this point I have confirmed reports from the Waldoboro area, Appleton, Stockton Springs, and a new site in Dixmont. I am fielding many, many pictures of things that are not late blight. The most common of these are leafhopper damage, early blight, Septoria leaf spot and Botrytis. I am getting the question often whether or not to spray, and to be safe I would be spraying, but at this point I still think the spread is going to be minimal so many folks may want to take the risk of not spraying. I hope I am not wrong.

Potato Leaf Hopper Damage. Photo by Eric Sideman.

The potato leaf hopper is wide spread in central and southern Maine. I am seeing lots of potatoes that have gone down and look like they died from a disease. I am also seeing the symptoms on beans (pale, yellowing leaves) and cucurbits (narrow yellow to browning edge on leaves). As I mentioned in earlier Pest Reports (ex. June 24), spraying for this pest must happen based on scouting and finding the insect. By the time you see symptoms on the plant, it is too late.

The white butterflies are flying all around the cabbage family plants now and laying eggs, and the larvae (green caterpillars) are chewing holes in the leaves. If you have heading broccoli you must know your customers because some folks are really turned off by the critters floating to the top of the water in the cooking pot. You may want to spray even though the crop is beyond risk.

Imported cabbage worm. Photo by Eric Sideman.
This pest overwinters as a pupa and there are 3-4 generations per year. This means that once you start seeing the butterfly you should start scouting for the caterpillar in about a week. Bt (Dipel 2X or Dipel DF) or Entrust work very well in controlling the caterpillar. None of these materials lasts in the field and so should only be sprayed when the caterpillars are there in large enough numbers to warrant it.

Destroy or bury crop residue after harvest so as not to allow the caterpillars to continue to feed and complete their life history and thus a larger second generation.

NOTE: Diamondback moth is also very common (see Pest Report July 7).

(Modified from a Report in the U Mass Vegetable Newsletter)
Japanese Beetles widespread and showing up in various crops and non-crop habitats, even though the numbers are down from years past. Oriental Beetles are also active and, though less damaging, may appear in vegetable fields as well. Asiatic Garden Beetles is evident mostly through their damage, because they feed at night. There are four species of scarab beetles that are common in New England turf, fruit and vegetable crops. These were all introduced to the US. Japanese beetles are the most common and widely distributed, but Oriental and Asiatic Garden beetles are expanding their range and activity. Below are brief descriptions.
  • JAPANESE BEETLE adults are about half an inch long, with a metallic green head. The wings are shiny copper or bronze color, and there are a few tufts of white “fur” along the side of each wing when it is folded back over the body. The adults are active in daylight and feed on many different kinds of trees, fruit and flower crops. Fruit and ornamental plants are preferred, but beetles can congregate in vegetables also. In vegetables, adults can cause silk clipping in corn, and leaf damage in sweet basil, collards, other greens, green beans, eggplant, asparagus, rhubarb, and peppers. Though numbers may be high, there is no need to treat unless actual feeding damage is significant. In corn, if there are more than two Japanese beetles per ear and corn is less than 50% pollinated, an application may be warranted to reduce clip¬ping and ensure adequate pollination.
  • Asiatic garden beetle. Photo by Eric Sideman.
  • ASIATIC GARDEN BEETLES are about half as long as a Japanese beetle adult, and somewhat more “plump” or domed in appearance. They are reddish-brown or dark copper-colored. They often are found near roots of plants when one is weeding. Adults tend to cause more damage to vegetable crops than Oriental Beetle, but less than Japanese beetles. Because they feed at night, one may find damage without seeing the beetles. During the day they hide in the loose soil or mulch around the base of the plants. Scout with a flashlight at night, or sift through soil to find them. Larvae feed on beet, carrot, corn, lettuce, onion, Swiss chard and strawberry. Adults feed on carrot, beet, parsnip, pepper and turnip. One grower reported heavy beetle feeding on peppers that were held under row cover through the end of June: this could be the result of Asiatic garden beetles that emerged under the cover. He could not find beetles, only damage. Beware the events that occur under row cover while unsuspecting farmers are looking the other way!
  • ORIENTAL BEETLES fly at night, but are very active during the day as well. The beetles are smaller than Japanese beetles, and usually are a rather mottled gray with black splotches. The pattern and color varies. Occasionally an individual will be al¬most all black or almost all gray. The antennae are branched and are quite striking if you take a close look. Oriental beetles have a long flight period – through early August – and are very mobile. Adults tend not to feed heavily in vegetable crop foliage. Grub damage may be worse in drought years and in weedy fields, but is not commonly a problem in vegetable fields and crops, though this is not well studied.
  • A fourth species may also be found: EUROPEAN CHAFERS, which are slightly larger than Japanese beetles and are a fairly dull brown or tan in color. They are night fliers but can be seen in large numbers just at sunset, when they congregate in large numbers in favorite trees (such as locust or willow). Adults are not foliage feeders and grubs are mostly a turf problem.
LIFE CYCLE . The life cycle of the Japanese beetle fits most of the spe¬cies of grubs we encounter in New England, with minor varia¬tions depending on the species and the location. They have a one-year life cycle, with adults emerging from the soil in July to feed and mate. The females burrow into the soil (often in or near wide expanses of grass or sod) to lay eggs, usually beginning in late July and August. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads). The first grubs usually appear around mid-August and begin feeding on roots of grasses and other plants (especially corn). After about two weeks of feeding, the grubs molt to a second “instar”, and feed for another three weeks. The grubs molt once more, to the “third instar” (or large grub) around the middle of September, and continue feeding until the soils begin to cool down. In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding for about six weeks. By the middle of June, most grubs have completed their feeding requirements and pupate (still in the soil) for about a week before emerging as new young adults.

CONTROLS. There are not many controls for organic growers to choose from. Beneficial nematodes work fairly well on the grubs if there before the population explodes, but for vegetable grower the adults are the critters that cause most damage and they are good fliers so your control of grubs in your sod fields will not likely reduce the damage. Neem and pyrethrum offer fair control of the adults.

R. Hazzard, adapted from Pat Vittum, Turf Entomologist, UMass, Beth Bishop, Michigan State University, Michael Seagraves, Cornell Cooperative Extension, and Ann Hazelrig, University of Vermont

Spider mite damange on cucumber plants. Photo by Eric Sideman.
Usually, natural enemies keep spider mites in check, but this year either the very dry weather or broad spectrum insecticides sprayed for leafhoppers or something else have lead to two spotted spider mite populations causing lots of damage. Spider mites puncture the cells of the leaves and extract juice. This results in the cell dying and the leaf getting a stippled appearance where the mites are feeding. As the feeding progresses the leaves become pale, mottled and then leather and then shriveled and desiccated. If you use a good magnifying glass (better yet, a hand lens) you can see the webbing caused by the mite, and the mites running around. They are very, very tiny. They are not insects (class Insecta) but are in the same class of Arthropods as spiders (class Arachnida) and have so 8 legs.

Scouting for mites should begin early in the season. They are more commonly a problem in greenhouse cucumber production than field production. In greenhouse production the release of predators is the best means of control. In field production one hopes for, and usually gets plenty of natural predators. Avoid spraying broad spectrum insecticides such as pyrethrum. If they build and it is early enough in the season to warrant control, neem oil and insecticidal soaps may help if the mites are spotted early.

Hornworms are probably the most destructive insect attacking tomatoes and they are showing up now in hoophouse tomatoes. They are giant caterpillars that can do a vast amount of eating in a very short time. Sometimes it seems that overnight healthy looking tomato plants are striped of their leaves leaving bare stems. The hornworms will also attack the fruit eating gouges out so large that they look more like bites of a furry animal than an insect. Look now for the damage and the frass, which is black pellets lying all around plants hosting hornworms. The frass may be your first sign there is a problem.

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

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

Bt works very well on this caterpillar, especially when they are small.


Braconid wasp parasites on tomato hornworm. Photo by Eric Sideman.
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)

August 23 | Page 3 of 15 | July 26


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