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 MOFGA's 2006 Pest Reports - Compiled by Eric Sideman, PhD Minimize

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LATE BLIGHT WARNING: [The following warning about late blight has been modified from notices from Steve Johnson in Umaine Coop Extension]

A late blight sighting has been confirmed in the Hartland, New Brunswick area and southern Aroostook County. The growers are aware of the situation. The sites are being handled as appropriate.

Late blight has been reported in Prince Edward Island.

Late blight has been reported in Long Island, New York. Some areas have had 24 inches of rain since planting.

All areas should be on a 5-day schedule.

SWEET CORN: [Reprinted from the Umaine IPM Sweet Corn Newsletter]

Corn Earworm Flight Threatens Silking Corn
Warm Weather Pushes Early Corn into Silk

Situation: Early corn planted under plastic mulch or rowcovers is now in the silk stage in southern Maine, while uncovered early fields are in the pre-tassel to tassel stage. Many late-planted fields are still in the whorl stage, but warm weather and plenty of soil moisture should move things along quickly. The warmer weather has also increased insect activity significantly, and we are now recommending protection for any silking corn in most areas of the state.

European Corn Borer: We continue to see significant European corn borer moth activity around the state, and an increase in larval feeding damage in many fields. Sprays on pre-silking corn for feeding damage exceeding the 15% action threshold were recommended in Auburn, Biddeford, Dayton, Dresden, Lewiston, North Berwick, Poland Spring, and Wells. Borer injury tends to be heaviest in fields with a history of corn production, or near other fields of silage or sweet corn. When corn reaches the silk stage sprays may be recommended based on the number of moths caught in pheromone traps. European corn borer moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving any visible feeding injury that would be noticed when scouting. Therefore, if more than five moths are caught in a week in a field with silking corn, a spray will be recommended. This week sprays to protect silking corn from corn borer were recommended in Lewiston, Readfield, Warren and Wayne. We do not recommend spraying silking fields for European corn borer if they are already being sprayed for corn earworm. Sprays for earworm should control both pests.

Corn Earworm: Moths are being caught in pheromone traps around much the state this week, resulting in recommendations to protect any silking corn in the area. The arrival of this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. Insecticide application recommendations for earworm are based on the number of moths caught in pheromone traps on a nightly basis. The greater the number of moths per night, the more frequently insecticides need to be applied to prevent infestation. This week a six-day spray interval to protect silking corn from corn earworm was recommended in Dayton, North Berwick and Wells. A 5 day spray interval was recommended in Auburn, and a 4 day spray interval was recommended in Cape Elizabeth and Nobleboro.

Fall Armyworm: We have not yet caught any fall armyworm moths in our pheromone traps around the state, and have not yet found any larval feeding damage in the field. This is usually the last serious corn insect pest to arrive in Maine, but it could appear any time now.

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

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

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

STRAWBERRY ROOT WORM: As foliage grows back after renovation, keep an eye out for feeding of strawberry rootworm (Paria fragariae). Strawberry leaves attacked by strawberry rootworm beetles are riddled with small holes. Some leaf damage occurs in May, but most occurs in July and August. Heavy infestations can reduce plant growth or kill plants.

Although adults of the strawberry rootworm feed on the leaves of strawberry, root-feeding by the larvae is more damaging to strawberry production. Adult strawberry rootworms are brown to black or copper-colored, shiny, oval-shaped beetles with four blotches on the shell-like wing covers. They are 1/8 inch long. The larvae are grubs that are 1/8 inch long, creamy white, with three pairs of legs. Adult strawberry rootworms overwinter in mulch and soil crevices, and become active in May and June. Adults feed primarily at night and hide in soil or mulch during the day. They chew small holes in leaves, and females lay eggs on older leaves near the soil surface. Larvae burrow into the ground to feed on strawberry roots from late spring to early summer. Small to large patches of dead plants may result. New adults begin emerging in mid-summer, and these beetles feed on strawberry foliage through early fall. Scouting for the presence of adult beetles is best done after dark using a flashlight to examine plants. No threshold has been established for this insect, but a population of 10 to 20 beetles per square foot is considered high. As with all the root feeding insects, control of the root feeding stage is very difficult. Therefore, control measures for strawberry rootworm should be directed toward the adult stage. If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and, therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again. The only control that really works for organic growers is to rotate out of the field after one or two years of picking.

POTATO LEAFHOPPER: Check new plantings of strawberries, beans and potatoes now for potato leafhopper (Empoasca fabae). I have seen these in small populations in the Brunswick and Bowdoinham area. Leafhoppers are sucking bugs that feed primarily on the underside of leaves, causing them to yellow between the veins and become curled and distorted. Feeding activity is most serious during the late spring and early summer. Leafhoppers are 1/8 inch long, green, bullet-shaped insects that take flight quickly if disturbed. The nymphs are light green and do not fly. Nymphs are easily identified by their habit of moving sideways when disturbed. Insecticides should be applied only when large populations of nymphs are noted on the leaves or symptoms first become apparent. By the time severe symptoms are seen it is too late to do anything. I believe the only material organic growers have that works is Pyganic, but if you think something else works let me know and I will pass it on.

BEANS: Mexican bean beetle has arrived in snap beans.. Look for coppery brown, spotted adults that look like large ladybeetles, yellow-orange egg masses, or bright yellow, oval spiny larvae. A beneficial insect, Pediobius foveolatus, is now commercially available for Mexican bean beetle control. This small, non-stinging, parasitic wasp attacks and kills Mexican bean beetle larvae. The parasite does not overwinter here, but provides excellent long-season control of the beetles. This wasp has been tested in snap beans and soybeans in New Jersey and Maryland. A single release, timed so that wasps can attack bean beetle larvae, can provide control. Wasps reproduce in the field and are still present when the second generation hatches out. To pronounce Pediobius, say "pee-dee-oh-bee-us". To purchase Pediobius contact:

ARBICO, 800-827-2847 (AZ), http://www.arbico.com/

The Beneficial Insect Company (NC), 336-973-8490


Rincon Vitova (CA), 800-248-2847




The Green Spot (NH), 603-943-8925

For more information, you can contact: Carol A. Holko, Maryland Department of Agriculture, Plant Protection and Weed Management Section, 410-841-5920, http://www.mda.state.md.us/plant/mex.htm

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