MOFGA Pest Report 2004
June 18

(View List Of All 2004 Pest Reports)

CROP CONDITION

The effects of the cool wet start here in Maine are still coming into view. Eggplant and tomato transplants are showing some stress. A purple leaf is a sign the plants are not taking up P from the soil. In wet, cool conditions, it is a good idea to increase P in the transplant solution. On the other hand, the recent warm weather is beginning to help and for the most part crops are coming out of it.

ONION SUNSCALD

This is a problem that resulted from the combination of the cool, wet weather that delayed planting and then the hot sun we have had this week. On the hot sunny days the temperature at the soil surface got very hot. The heat damaged the sensitive young onion seedlings that were just germinating. The injured tissue shriveled, strangling the neck right at the soil line, and the plant wilts and withers. The only way to avoid sunscald is to plant seed as early as possible so that the plants are beyond the sensitive stage before the soil temperature becomes too hot.

POTATO LATE BLIGHT

It looks like we may have a perfect late blight kind of year. Cool, wet conditions favor late blight. Check your potato cull piles. Cull piles are the chief source of the initial late blight infection. Bury the pile with at least 2 feet of soil or cover with a black plastic tarp.

POTATO LEAFHOPPER

Brian Caldwell saw potato leafhoppers on potatoes in Livingston County, NY. He also received a report that they are in the Hudson Valley. This is earlier than normal, even in New York.

Check potatoes for potato leafhoppers (PLH). Walk out into your potatoes and brush the leaves with your hand. If you see small white things darting around, you've got potato leaf hopper adults. Once you see them, look closely at several leaves. You may see small, elongated light green insects scurrying to hide from you-these are potato leafhopper nymphs. The IPM threshold for this pest is very low.

Later-maturing varieties including Katahdin, Elba, Green Mountain, Kennebec, and Blossom have some resistance, and likely will not need spraying. Yukon Gold, Red Norland, and most other varieties, are very susceptible.

PLH controls are not often used on organic farms, perhaps because growers don't realize how much yield loss this pest can cause. Pyganic EC, an approved pyrethrum product, is reported to be effective against PLH. Two to three sprays of Pyganic, 7-10 days apart, as soon as you find significant numbers of adults in your planting, should halt their damage and prevent a buildup of nymphs. Surround has been tested, and, unfortunately, does not appear to be very effect against PLH.

Beans are also a favorite so make sure you scout your beans.

From a report by Brian Caldwell
Farm Education Coordinator
Northeast Organic Farming Association of New York

COLORADO POTATO BEETLE

Colorado potato beetle eggs have been showing up this week in potato and eggplant. Soon warm temperatures will push adults to mate, feed and lay eggs at a steady pace. Eggs hatch within 5 to 12 days, depending upon temperatures. At 60 degrees F (constant temperature.) eggs hatch in 12 days; while at 75 degrees F, hatch occurs in just 5 days. Of course, the average daily field temperatures vary widely from day to day; these numbers simply give you a ballpark estimate of when to expect eggs to hatch under the range of temperatures we see in New England in June.

All insecticides are most effective on very young larvae. Eggs and pupae are not susceptible to chemical control and adults can be difficult to control. Targeting application to-ward young larvae helps prevent damaging populations and allows resistant adult beetles to mate with susceptible beetles keeping selection pressure for insecticides resistance low. If sprays are targeted against overwintering adults, the only survivors will be resistant individuals. When resistant individuals mate, their offspring are resistant thus fixing the resistance gene in the population. Once resistance has become fixed in a population, reversion to susceptibility occurs only after many generations of non-exposure and may never revert to pre-exposure levels I recommend that the later season CPB be allowed to overwinter for the same reason. Later in the season potatoes can take quite a bit of defoliation without reduced yield and you will be allowing susceptible genes to persist in the population.

CPB is the king (queen?) of insecticide resistance. This beetle has developed resistance to every insecticide that has been used to control it. We all recommend using other chemistries wherever possible! However, organic growers are left with only the very effective Entrust. Novodor (Bt) is very effective when used against young larvae up to the third instar, but it has not been reformulated as of yet and the present formulation of this Bt has not been approved for use on organic farms. Please give Valent, the company that manufactures it, a call (1800 323 9597) and ask them to reformulate for organic growers. In the mean time, be very careful not to overuse the Entrust.

Foliar materials are best applied between 15 and 30% egg hatch for optimum control. A second foliar application may be necessary if egg laying continues over an extended period. You can predict 15-30% egg hatch by flagging egg masses in the field and checking them daily. Alternatively, insecticide application could begin when egg hatch has occurred on 5-10% of the plants. Waiting to spray until beetles are in the late 3rd and early 4th instar is not a wise strategy. Large larvae are difficult to control and since the 4th instar larvae are responsible as much as 75% of the feeding damage, earlier treatment is usually necessary to prevent economic damage. Determining if a beetle population is large enough to treat is not easy. Potatoes can tolerate up to 30% defoliation prior to flowering but only 10% defoliation at the onset of tuber initiation. Failure to control the first generation larvae may translate into large numbers of summer adults that emerge and feed during the critical tuber initiation and tuber bulking stage.

(modified from a report in UMASS Vegetable Newsletter which was -Adapted from D. Ragsdale and E. Radcliffe, Department of En-tomology, University of Minnesota.

TOMATOES AND PEPPERS

Bacterial canker and speck can be problems on tomato foliage and fruit in wet seasons. Bacterial spot can affect both tomatoes and peppers. Canker is systemic in the plant causing curling and marginal leaf burn. Speck and spot cause small black, slightly raised lesions on foliage. If you have had a history of bacterial disease on your farm, it can make a difference to apply copper (tomatoes) or copper (peppers) within a week or two after transplanting. If you observe the disease in your plantings, a weekly application is recommended. Are you not sure if what you see is a bacterial disease? Contact Rob Wick at the UMass Disease Diagnostic Lab, 413-545-1045. In Massachusetts tomatoes, bacterial canker has been the most common bacterial disease, but we have observed all of these diseases on Massachusetts farms in past years. Cultural practices also make a difference: don't prune or handle the plants when they're wet to avoid spreading disease. We've seen it spread down a row, presumably during pruning or tying. It's also spread by wind-blown rain, and by airblast sprayers.

modified from a report in UMASS Vegetable Newsletter which was - adapted by R Hazzard from OWYS Weekly Vegetable Update, Cornell Cooperative Extension, 6/09/2004, C.R. MacNeil & Julie Kikkert

CUTWORMS ON TRANSPLANTS

We have had numerous reports of cutworm damage in transplants and seedlings of brassicas, cucurbits and other crops. Typical damage includes clipped stems as well as leaf feeding, indicating that these cutworms are climbing up into foliage. If the soil near the plant is searched during the day, one or more cutworms can be found curled up in the soil.

The cutworm is a caterpillar that lives buried in the soil during the day and comes out to feed at night. The moths fly in and lay eggs on plants. Some species arrive very early in the spring, others arrive in the summer or fall and overwinter. In both cases weeds swell the problem because they provide a great egg laying site for the moths. Growers notice the problem in the spring mostly because we have just cleared the fields of most of the food for the cutworms (by tilling or plowing) and planted only a small bit to re-place it, i.e., our transplants or newly emerged seedlings.

There are many species of cutworms that attack vegetables; the most common in this region are black cutworm (Agro-tis ipsilon) and variegated cutworm (Peridroma saucia). Others may include dingy, spotted, dark-sided, or glassy cutworm. Both black and variegated cutworms climb onto foliage. Variegated cutworm has some pale yellow mark-ings on its back, while black cutworm is nearly uniform gray to black with a greasy, rough appearance. Samples coming in to our lab at UMass appear to be black cutworm.

Black cutworm migrates northward annually, with the first moths arriving in early spring. The females deposit eggs in areas such as low, waterlogged or flooded spots in fields, and in sites overgrown with grasses or winter annual weeds. Weeds that are attractive to egg-laying moths include chick-weed, shepherd's purse, peppergrass, and mustards such as yellow rocket. Winter wheat and alfalfa are also likely hosts; other cover crops may also be hosts. Eggs hatch in 5-7 days. Small larvae feed on plant leaves, so early cutworm feeding shows up as small irregular holes in the leaves. The larvae feed above ground for about the first quarter of their lives, or until they are approximately half an inch long. Black cutworms do not begin to cut plants until they reach the 4th instar. Larval development takes about a month (28-34 days). Pupation takes place in the soil; the complete life cycle from egg to adult moths requires about 45 days.

Monitoring- Scout weed borders before plantings go in. Check newly transplanted or emerged crops to as-sess presence and severity of cutworms before the damage is severe. Estimate % stand loss to determine need for a spray.

Adult moths of the black or variegated cutworm can be monitored with bucket traps (the Unitrap or Multipher trap, baited with the appropriate lure, with a vaporstrip to kill moths) placed in fields or weedy areas near the field. This would indicate high levels of moth activity, help predict egg laying, and warn of future problems. Trap sources: Great lakes IPM (800-235-0285 ) or Gemplers (800-382-8473).

Cultural Management- Weedy land harbors the most cutworms, as the adult moths seem to prefer dense plant cover for egg laying. Crop residues may also attract higher populations. Therefore, crops that follow weedy crops, alfalfa, or no-till crops are more likely to be dam-aged by cutworms. Plant early transplants into fields that had low weed pressure the previous year, or where crop residue was tilled under in the fall. Plow fields in spring and keep weed free for at least two weeks before planting to starve young larvae and reduce egg-laying. Avoid plant-ing susceptible crops close to sod, alfalfa or fallow areas. Summer plowing or discing disturbs eggs and larvae and raises them to the soil surface where they are more vulner-able to predation and dessication. Plan rotations to avoid row or hill crops following a grassy sod, and plow sod fields in later summer or early fall.

We would all like to know more about the relationship between cover crop systems and cutworms. Outbreaks seems to be unpredictable and it is not clear if they are related to particular cover crops. I would welcome any observations or research information on this topic.

Another suggestion is to plant a thick "trap crop" of sun-flower, a favored host, around the perimeter of the field, then find and kill cutworms in this crop.

Biological management- Several predators and parasites have been identified, however none have been commercialized for release against these pests. At Iowa State University, a new virus has been isolated from black cutworm which is highly active and has potential as an alternative to chemical control. Work is ongoing to evaluate this unique strain of baculovirus and the most effective way to use it in the field. Soil applications of nematodes have been evaluated with mixed success. Daily search and destroy missions -- by hand -- are a time-honored "biological" management for small plantings!

Chemical management- Directed applications (banded or directed to foliage and soil surface) of insecticides will control cutworms. For best results apply in the evening just prior to active feeding. Check New England Vegetable Management Guide for specific materials and follow label instructions for the target crop (crop registra-tions do vary!).

This is a tough pest for organic growers as no effective broad-spectrum products are available. Strategies such as cardboard or tinfoil collars work but are impractical on a commercial scale. Eric Sideman, technical advisor for Maine Organic Farming and Gardening Association (MOF-GA) reports that insecticidal baits have been effective. He recommends a recipe using a very concentrated solution of Bt, mixed with bran and a bit of molasses. It can be sprinkled on the ground near the crops or made into patties that are placed along the rows. Bt sprays (ie, Bt aizawi or kurstaki) directed at plant stems and foliage) are another possible control, especially for cutworms that are foliar feeding. Apply the spray in the evening when the cutworm activity is greatest. The main challenge if you have large cutworms is to get them to ingest a big enough dose of BT to stop feeding and die before they destroy the seedling.

--R. Hazzard with input from Brian Caldwel, NOFA-NY, Eric Side-man, MOFGA, & Vern Grnbinge, Univ. of VT Extension

STRAWBERRIES

Situation: Recent warm weather has hastened ripening in much of the state. Harvest has begun in some southern fields and in plantings that were under rowcovers. Pick your own fields are expected to start opening this weekend in some locations. Although the harvest looks to be a little bit late, and a little bit light in most locations, quality is good, and demand appears to be strong.

Strawberry bud weevil or "clipper": While most fields around the state are beyond the stage where clipper can cause significant economic harm, there may still be a few fields in northern Maine that should still be scouting for clipper. We have been finding plenty of adult clippers around, but we do not recommend a control if the field is past bloom.

Tarnished plant bug
With the exception of a few fields, tarnished plant bug has been noticeable by its absence so far this season. Adult bugs are still active and, we presume, are still laying eggs. So it is not too late for this insect to become a problem in fields that are still in the bloom to petal fall stage. Fields in North Berwick, Poland Spring and Monmouth over the threshold of 4 out of 30 flower clusters scouted infested with tarnished plant bug nymphs. Remember that this insect can remain a pest well into the fruit development stage, so growers should continue scouting for it.

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 have now proven materials for these weevils or the clipper or root worm. If you are seeing a lot of damage it is time to plow this field after harvest and have a new field far away next year. How far? I don't know, the further the better.

(modified from Strawberry IPM Newsletter No. 5 by David Handley, U Maine)

CABBAGE MOTH

I saw the first cabbage moths this week. Remember, Bt is very effective against the caterpillar but has a very short life in field conditions. There is no point in spraying until you see the caterpillars.

(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.)