MOFGA Pest Report 2004
June 29, 2004

(View List Of All 2004 Pest Reports)

PEAS: FUSARIUM WILT

There are at least 6 races of Fusarium of peas and it would take a lab culture to determine which one is out there but there is one in my peas. Symptoms of the races differ slightly. The key is yellowing of the leaves starting with the lower leaves and working up the plant. In hot weather, which may come eventually even in Maine, the disease progresses very rapidly and the whole plant will yellow and die in less then a week. The stem turns brittle near the soil line but the root system often is healthy looking.

The disease is caused by Fusarium oxysporum, which can persist in the soil for over 10 years. It is disseminated through the movement of contaminated soil, plant fragments, water, wind, tools, etc. It is commonly transmitted by contaminated and infected seed.

In my field I have three varieties of peas and only my snow pea has it.

The only economical control of Fusarium wilt of peas is varietal resistance. Of course, good cultural practices are necessary too. Rotation and sanitation is a must if you have this in your soil in one field and not yet in another. Early planting so peas mature before the soil warms and the disease spreads rapidly helps.

SWEET CORN, GRAIN, GRASS: COMMON ARMYWORM

Almost every year some locality east of the Rocky Mountains gets hit hard by marching armies of caterpillars eating grass including hay, small grains and corn. In 2001 it was Maine's turn. This year I am beginning to see and hear about some damage in central Maine. Nothing bad yet, but let's all keep our eyes open. Let me know if you have the damage. The damage I am seeing now is in sweet corn where the caterpillar is feeding in the whorl and the leaves have large ragged edges and holes, and there are masses of sawdust-like excrement. It is probably not economically worth trying to control this pest until about 15% of the corn is damaged and I am not seeing anywhere near that level yet...

The critter is the common armyworm. Luckily there are many natural enemies of the army worm and it is rarely a major problem two years in a row in any location because as the pest populations build up so do its natural enemies. As predicted, even after a bad battle in 2001 there was nearly no damage in 2002 or 2003. There are many natural enemies of the army worm including ground beetles, parasitic wasps, and birds. The most effective enemy is the red-tailed tachina-fly.

The armyworm is related to the cut worm and somewhat has that same greasy appearance. They are gray to black with a narrow yellow stripe on their back and a wider yellow stripe on each side.

There is some question as to whether the army worm can over winter in Maine. Where it does, it over winters as a hibernating, partially grown caterpillar. The young larvae feed in the spring, not usually doing much damage, pupate in May, and the moths of the first generation appear in June. The females lay about seven hundred eggs each that hatch in about ten days. The moths tend to cluster when egg laying and so you see patches of very dense populations of caterpillars. The caterpillars from these eggs are the destructive worms that you see now feeding. The worms feed mostly at night when their enemies are sleeping. Leaves of grass are their favorite food and many fields of hay and small grains were destroyed in 2001. As the worm finishes the food in an area they march along spreading out from the patch and devouring grass along the way, hence the name army worm.

It takes about three to four weeks for the worms to reach their full grown size of about 1.5 to 2 inches, at which time they burrow into the soil and pupate. New moths emerge in about two weeks. These lay eggs for another generation of army worms but these are not unsually as destructive as the earlier generation.

Controls
The best pesticides available to organic growers are probably a Bt and spinosad. Dipel Df (2 lb/A) or Xenteri (1.5 lb/A) and Entrust (1-2 oz/A) are labeled for armyworm.

STRAWBERRY: Harvest Season Pests

(Modified from U. Maine, Strawberry IPM Newsletter)

Sap beetles chew small holes and tunnels in ripening fruit, similar to slug injury. These beetles are about 1/8 inch long and dark brown in color. They can be hard to find because they drop to the ground when disturbed. They are usually found during harvest in the cavities of chewed fruit. The best management for this pest is sanitation. Keep the field free of over ripe fruit by picking the plants thoroughly and regularly. Some growers have tried trapping sap beetles with bait baskets of over-ripe fruit or backs of bread dough placed along the edges of the field and wooded areas. The idea is to prevent the beetles from moving into the field. Results with this technique have been variable.

Black Vine & Strawberry Root Weevils:
As we get into the harvest season it is also time for the adult black vine and strawberry root weevils to begin to emerge and start feeding on strawberry foliage. Look for notching along the leaf edges and the presence of the black or brown snout beetles. These insects do most of their feeding at night and spend the daylight hours at the base of the plants under the mulch. These insects will be laying eggs and the larvae or grubs will feed on the strawberry plant roots through the fall and again next spring, causing plants to weaken and die. Organic growers should rotate fields on a 1-2 year basis to avoid these insects.

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)