Eric Sideman's Pest Report
June 21, 2002

NOTE: This is the last pest report I will send to my old list of growers. Next week I will have the report sent to the new MOFGA Certification Services, LLC list of certified growers. If you do not receive another pest report after this one by July 4, that means you are not on the list. If you do not receive the next pest report and you want to continue getting them, send a note Dawn at the MOFGA office at mofga@mofga.org.

Crop Condition

Today is the first day of summer and it is very warm and there is plenty of soil moisture and so I expect crops will finally start growing at a normal pace. Up until now it has been cool or cold and the soil has been very moist. These conditions have three effects on crops. First of all, seeds germinate very slowly. I have heard reports of seed rotting before it germinated in the cool soil we had this spring, especially bean and corn. Early corn will be scarce this year! A major cause of this is the seed corn maggot that in cool soil has a good chance at the sitting-duck seeds (see below). Warm weather crops just do not grow. In addition, there is little microbial activity in the soil so there is little nutrient made available to crops. Many crops I have seen, especially tomatoes, corn and the squash family are stunted. The next few days should turn things around.

POTATO:

BE READY FOR COLORADO POTATO BEETLE EGG HATCH
I have received early reports of Colorado potato beetles (CPB) moving into potato fields and laying eggs in southern Maine. Walk your fields and look for CPB adults and eggs. Except for field edges in non-rotated fields, adult beetles do not usually cause enough damage to early potatoes to require control. The economic threshold for adult beetles in potato is 1 beetle per 2 plants (or per 2 stalks, in midseason).

Scouting. Look on the undersides of leaves for the orange-yellow egg masses. The fresher the eggs, the brighter orange the eggs will appear. If eggs have been around for a while, they appear more orangish then turn a dark brown . When you find eggs, flag ten egg masses with bright tape or flags, and then keep an eye on the hatch. This will tell you when the earliest eggs are hatching.

Timing and thresholds. If you are using Bt’s, you want to apply the Bt when 20-30% of the eggs have hatched and then again a week or so later when the rest are done hatching. If you are good with the timing you may be done spraying for the season, unless you are close enough to other growers who do not control their CPB and second generation adults fly into your fields.

With cool conditions, beetle invasion of fields, egg deposition and then hatch can be spread out over a long period of time. This situation is not good as then you can have various stages of larvae as well as adults in your field. Or, if it warms up suddenly, you will have a rapid flush of larval hatch and feeding damage that may seem to explode out of nowhere. 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 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. And, worst of all for organic growers is that the Bt is only really effective on the small larvae.

The two Bt formulations that are approved for this season are CPB Beater and Novodor.

NOTE: These may not be approved for next season because they are formulated with inert ingredients that may not be permitted. Please find time to call the manufacturer and tell them how important the Bt is to your farm and that you would like them to work on getting Novodor approved for organic use. (Adapted from John Mishanec, UMass IPM Vegetable Program)

THREE LINED POTATO BUG (Lema trilineata)

This beetle is sometimes confused with the cucumber beetle and growers wonder what the cucumber beetle is doing feeding on plants in the tomato family, especially tomatillo. It is not a cucumber beetle but what is sometimes referred to as the old fashion potato beetle. It is dark yellow with three black stripes and the adults are out now in force feeding on leaves. The larvae are smaller than CPB larvae and have the distasteful habit of carrying a pile of excrement on their back. Usually these do not wipe out a crop, but on ornamental plants they sure can make it look ugly. I would only spray with rotenone as a last resort.

LATE BLIGHT
Bury cull piles and kill volunteer sprouts in last year's fields. It looks like we are beginning to have a perfect late blight kind of year. Cool, wet conditions favor late blight (LB). With that in mind, before things get too busy, it’s a good idea to check your potato cull piles. Cull piles are a good source of LB. It can be carried over from the previous year or unsprayed potato plants will be more susceptible. Bury the pile with at least 2 feet of soil or cover with a black plastic tarp.

LEAFHOPPERS
Potato Leafhoppers normally begin to appear in fields around late June. Often leafhoppers cause serious damage before thegrower knows they are present. Leaf bronzing or "hopperburn"’ can cause serious reduction in yields. Look for the greenish adults under leaves. Adults quickly fly off when disturbed. Later, the light green or tan nymphs are easier to detect. Leafhoppers can be monitored using a sweep net or by searching the underside of the leaves. With a sweep net, make 5 sweeps across a row at five locations in the field. Control is suggested on potatoes if there is more than one leafhopper per sweep or 5 nymphs per 50 leaves. If you don’t have a sweep net, search under leaves and note adults or nymphs. If you find an average of 1 per 10 leaves, control is recommended. A third method is to flop the vines into the row and shake the plant vigorously. Look on the ground for leafhoppers that fall off the plant. Pyrethrum will work to control this pest. Be sure to spray undersides of leaves. ( adapted by me from adaption by R Hazzard from J. Mishanec and M. Baker)

WEB SOURCE FOR DISEASE IDENTIFICATION
An excellent new web resource for disease identification is the New York State’s Vegetable MD Online. This is a site produced by the Plant Pathology Department at Cornell. It has great pictures. You can go through a selected crop and learn about any disease that might affect that crop. Did I mention it has great pictures? Check it out. The web location is:

http://VegetableMDOnline.ppath.cornell.edu/Home.htm

SEEDCORN MAGGOT INFESTATIONS: WHAT TO DO?
(I may be a bit late getting this one to you but this was a problem here a few weeks ago Many fields have already been replanted.

This spring, growers have reported seedcorn maggot in many vegetable plantings. Cool, wet weather is ideal for seedcorn maggot growth and development. Bean, corn and vine crop fields are most commonly attacked, although the seedcorn maggot has a fairly wide host range. The adults, small gray flies that look like houseflies, are attracted to soils rich in organic matter for egg laying. Applying manure to soils or plowing down green manure increases the attractiveness of soil for several weeks. Growers should delay planting into such soils. Once a field has been infested with seedcorn maggots, there is no remedy but to replant. Insecticides cannot salvage fields already infested. If a grower chooses to replant, there are several ways to prevent damage to the second planting. The best solution is to delay replanting until the maggots have matured and the soil has warmed so that the seeds germinate quickly. Mature maggots are about a quarter of an inch long. If a grower finds maggots this size in the field and waits about a week to replant, it should be okay. If maggots are smaller, growers should wait about one and a half to two weeks to replant. Planting into soils where maggots are present is risky. The best strategy is to wait. Once the soils warm to around 70° F, there is little danger of damage from seedcorn maggot. (adapted from B. Bishop & W.Pett, Michigan State)

TOMATO

Cat-facing on early tomatoes may be a problem this year, as a result of cold temperatures during flower formation in May. Nothing can be done by the time you see symptoms except to hope that the next cluster was not subject to such extreme cold.

In greenhouse tomatoes, watch for Botrytis. Cool, dark days favor the development of this disease. Botrytis blight produces characteristic gray fuzzy appearing spores on the surface of infected leaves or fruit. Air currents and splashing water can easily spread the spores. Control of the environment is very important in controlling this disease. Keep humidity below 93% by heating and ventilating. Avoid wetting the foliage during times when drying is slow. TopShield, Trichderma harzianum, is a beneficial fungus which can suppress Botryitis if used as a preventative. It does not cure diseased plants. Oxidate has been reported to help in houses that have had problems. By far managing ventilation and keeping the plants well pruned are the best tools.

Where bacterial diseases have been a problem on your farm, early applications of copper are recommended to prevent outbreaks later in the season. Recent wet, cool weather favors the development of bacterial diseases.

CRUCIFERS

Cabbage root maggots are showing up in plant roots in untreated fields of early brassicas, causing scattered wilt and death of plants and ruined radish. Organic rescue treatments are not effective. New plantings should not need treatments for root maggot any more this season. Diamondback moth and imported cabbageworm have not been observed yet.

CUCURBITS

STRIPED CUCUMBER BEETLE

Striped cucumber beetles are becoming active and numbers are likely to jump rapidly this week. I observed large numbers on zucchini in a non-rotated field. Direct-seeded pumpkin, winter squash, melons and cucumbers that are just emerging, as well as transplants that are still young are highly susceptible to both feeding damage and transmission of bacterial wilt, which is vectored by the cucumber beetle. The cotyledon up to the five-leaf stage is most susceptible.

Beetles are very mobile and can build up rapidly, so fields should be scouted at least twice a week. Activity tends to be high during hot sunny weather. Rotation makes a difference! Numbers will be higher and infestation earlier in non-rotated fields.

Scouting. Look for signs of feeding on the underside of leaves, especially the cotyledons. Beetles are often found underneath leaves or in cracks in the soil. Check sets of 5 plants in at least five areas of the field (25 plants total), counting number of beetles on or near the plant. This can be done in about 20 minutes. Check field edges for hot spots. Beetles often colonize from field edges and numbers will be higher in the first rows near a woods or fallow area. Border treatments or border trap crops may help reduce infestation of the whole field.

Row covers work very well in excluding the beetle. Be sure to get the row covers on before the beetles arrive. Also, remember to weed and you need to take the covers off at blossom time for pollinators.

Successful management of the cucumber beetle has been reported using Surround. Surround is a formulation of kaolin clay that coats the leaves. Here are some tips on using Surround WP as reported in the UMASS Newsletter:

• Apply before beetles arrive. This acts as a repellent and anti-feedent so must be present before damage is done.
• If you are using transplants, apply before setting them out. This saves time and materials.
• With direct-seeded crops, apply as soon as seedlings emerge if beetles are active.
• Ensure good coverage of the foliage (it will look like it was sprayed with white latex paint), including, if possible, the undersides of leaves (not easy when cotyledons are close to the ground).
• Reapply after a heavy rain
• Be sure to mix a slurry in a bucket and then add the slurry to the tank, as the dry powder could cake if added directly to the tank mix.
• Continuous agitation is needed.

ARMYWORM ALERT

It looks like common armyworm is in Mass. again - probably not on the same scale as last year, but at damaging levels in some fields. Only a few adults have been trapped in Maine. Typically, the year following a serious infestation does not bring serious outbreaks. However, George Murphy of Crop Production Services reports that they found heavy numbers of armyworm larvae feeding in field corn crops in two different fields in the Connecticut Valley, one in Deerfield and one in W. Northfield. They found one or two caterpillars (about 1 1/2 inches long) per plant and significant feeding damage. Where pheromone traps have been deployed at several locations in the Valley for the past two weeks, no moths have been captured. However, these infestations probably came from an earlier flight. There could have been an early migratory moth flight into the northeast, or it is possible that some pupae survived the mild winter.

This insect attacks grass and hay crops, field corn and sweet corn. Moths are pale gray-brown with a white dot near the center of the wing, but are seldom seen since they fly at night. Eggs are laid in folded leaves or leaf sheaths.

To Scout: check corn for damaged leaves appear to have been shredded, which is characteristic of both the common and fall armyworms. Typically, damage begins near the edge of a field as the caterpillars move in from neighboring fields. Be particularly watchful in fields that border hay. The young worms are pale green in color and have the looping habit of crawling until about half grown. The mature caterpillar is about 1 to 2 inches long, dark green and hairless with five whitish stripes along the length of the body. The head is a pale green-brown with darker mottling. Typically they feed at night and hide in the soil during the day. The best time to scout is in the evening or early morning. Each field should be scouted separately, because infestations can vary from field to field, even with fields that are close to each other.

Armyworms are heavy feeders on the leaves, in the whorl and in the ear. The threshold for these caterpillars in sweet corn is the same as for fall armyworm: control when damage exceeds 15% in the whorl or pretassel stages. Control in sweet corn is with Bt. I will keep you informed of this and other corn pests as they arrive. (adapted from the UMASS Newsletter)

(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.)