MOFGA Pest Report 2004
11 August

(View List Of All 2004 Pest Reports)

Sweet Corn IPM Newsletter

(modified from report by Dave Handley, Umaine COOP Ext.)

Fall Armyworm Pressure on the Rise

Earworm: Highest Pressure of the Season in Southern Maine

SITUATION Corn harvest is in full swing in most of the state. Fluctuating temperatures and some rain have made the pest situation highly variable form field to field, with generally high pest pressure in southern Maine and moderate pest pressure in the midstate region. Growers are encouraged to closely monitor their fields for sudden infestations moving in from the south and west.

European Corn Borer: Pheromone trap catches were very low in general this week, with a slight rise in the most southern locations. Larval feeding injury was also very low, but fall armyworm damage continues to be high, keeping young fields at risk.

Although moth counts were generally low this week, the threshold for European corn borer moths in silking corn was exceeded in Biddeford, Cape Elizabeth, Dayton, and North Berwick. However, all of these fields were already under a spray interval for corn earworm, so no additional sprays should be needed.

Corn Earworm: Moth populations were very variable this week, breaking season records in some locations, but being very low in others. Situations like this illustrate the importance of scouting your own fields, because the populations can vary greatly even over a distance of just a few miles. This week a three day spray interval was recommended on silking corn in No. Berwick and Wells. A four day spray interval was recommended in Biddeford, Cape Elizabeth, Dayton, Dresden, East Corinth, Levant, Lewiston, Litchfield, New Gloucester, Poland Spring, Warren and Wayne. A five day spray interval was recommended for China and Oxford. A six day spray interval was recommended for Garland and Nobleboro. No spray was recommended in Farmington.

Fall Armyworm: Fall Armyworm moth captures remained high in most locations this week. Sprays for moths are recommended on silking corn when three or more moths are caught in a week. This week the threshold was exceeded in Biddeford, Cape Elizabeth, Dayton, Dresden, Garland, Lewiston, New Gloucester, No. Berwick, Oxford, Poland Spring and Wells. However, these locations were already on a spray interval for corn earworm, so no additional spray was required. Fall armyworm larval feeding injury has increased and was found in most locations in southern Maine. This injury is combined with European corn borer injury to determine if protection is needed. Control thresholds are 30% infestation in whorl stage corn or 15% for corn at pre-tassel and beyond. Injury exceeded control thresholds in Cape Elizabeth, Dayton, Litchfield, Monmouth and Poland Spring.

Twilight Meeting: Thursday, August 26th
Johnny's Selected Seeds, Foss Hill Road, Albion, Maine. Self guided tours 5-6:00, Guided tours, Q&A 6:00 until dusk. Come see what is new in the world of new vegetables, flowers, and herbs. Members of Johnny's research staff will lead us through the trial plots, pointing out exciting new varieties and will describe how they determine what varieties to include in their offerings.

BEANS

Beans all over the state are showing interveinal chlorosis on the younger leaves (yellowing between the veins). This is a sign of a nutrient deficiency, but I think it is really a symptom of the weather we have had this summer. Nutrients may not really be lacking in the soil but the wet, cool (less than ideal for beans) weather we have had has induced a nutrient deficiency. The most likely in my reading seems to be iron, but manganese or magnesium would have the same symptoms. If you are really gong ho about it you can try spraying a seaweed mix, but I think it is so late in the season and beans are so far along I would just hope that there is enough there to get a reasonable yield.

White mold is another story. Again, the wet weather is to blame, mostly. Of course, if you did not have white mold spores in the soil you would not have it on your plants now. White mold is a fungus (Sclerotinia sclerotiorum) that can effect all parts of the bean plant but is most common deep in the canopy, where it is continually damp, on the beans themselves and on the stem. The disease typically becomes serious in crops that are crowded together, in years that are cool and moistŠ.like this year. White mold over winters as sclerotia (hard resting bodies of vegetative tissue) that sprout in the spring and release the spores. If the conditions are right, the spores germinate when they land on a host and grow into this very white mycelium. Soon, new sclerotia are formed that fall to the soil and can remain dormant there for many years until conditions are right to germinate. In addition to the long dormancy, white mold is hard to get rid of by crop rotation because it has quite a few other hosts besides beans, including carrots, tomatoes, peppers and lettuce. Corn and grass cover crops make good choices for rotation if you are trying to clean up a field where white mold has been a big problem. Also, there is a new material made from an antagonistic fungus that attacks the slcerotia called Contans. If you would like info on this go to the web site www.encoretechllc.com.

BRASSICAS: CATERPILLARS AND FLEA BEETLES

(modified from an article by Ruth Hazzard in the UMASS Vegetable Newsletter)

Its not news that diamondback moths (DBM) and imported cabbage worms (ICW) are active in brassica fields. Growers should be scouting for these pests. Cab-bage loopers (CL) have not been reported yet but could also be present. When scouting for 'worms', be sure to look beneath the leaves and on the inner most portions of the plants. Look for feeding damage as well as for caterpil-lars. Tiny feeding holes are often easier to spot than small green caterpillars. Apply controls when thresholds are reached, and direct materials at the undersides of leaves as much as possible. Use at least 50 gal/A of water to achieve better spray coverage, and use a spreader-sticker.

A threshold of 15%-infested plants (an 'infested' plant has at least one caterpillar of any species) is recommended for any heading cabbage, broccoli, and all leafy greens. Before the cupping stage, in cabbage and broccoli, use a threshold of 35% plants infested. These thresholds provide a clean crop at harvest. Cauliflower use a 10% threshold.

An excellent comparison of "worm" insects at various life stages can be found at the following website : http://www.ces.ncsu.edu/depts/ent/notes/Vegetables/veg012e/cwcompho.htm.

Imported Cabbageworm: The larva is a slow-moving, velvety-green caterpillar, which grows through a series of five stages, or instars, to a length of 1 1/4 inches. Larger caterpillars have a delicate yellow line that runs lengthwise down the center of their bodies. Small larvae feed on the undersides of outer leaves after hatching. Larger larvae are more mobile and are often found in the florets of broccoli or feeding on the heads of cabbage. Larvae may also move to neighboring plants.

Diamondback Moth larvae grow through four instars to a length of 1/3-inch. They are light green; tapering to points on both ends and appearing scalloped or segmented along the edges of their bodies. During the first two instars, the larvae have black heads, which later lighten to match their green bodies. They can be distinguished from other caterpillar pests by their habit of wiggling frantically when touched or disturbed. They may also drop from the plant and suspend themselves on a silken thread until the disturbance passes. The larval stage lasts from two to four weeks, depending upon temperatures. Pupae are found attached to the undersides of crop foliage and appear to be thinly veiled under a fine, net-like silken cocoon.

The cabbage looper caterpillar is light green, with wavy white or light yellow lines down the back and sides. Full-grown larvae reach 1 1/2 to 2 inches. At rest or when disturbed, cabbage loopers of any size will raise the middle of their body in a characteristic "loop" shape. Eggs are round, light green or yellow, and laid underneath the foliage. Feeding tends to create ragged, large holes in foliage, on both frame leaves and heads. Moths arrive in New England on migratory flights from the south, like corn earworm. Insecticides for Caterpillars: In the area of caterpillar control there are two very effective products available to organic growers. The material spinosad is available in an organic formulation called Entrust (this material is also effective for Colorado potato beetle, thrips and leaf miners). Both Bt aizawi (eg Xentari) and Bt kurstaki ( eg Dipel,) products work well; Bt aizawi is recommended when diamondback moth is the dominant species. It is possible to get excellent control of the three major caterpillar pests using low-risk products that are safe to handle and conserve beneficial insects (which do have an impact in suppressing aphids and caterpillars). It is also easier now to rotate among different types of products, to prevent selecting for resistance to any single product.

Flea beetle numbers have gone down - it is likely that we are between adult generations - pupae and larvae are in the soil, near the roots of early brassicas. We are starting to see an increase in numbers of striped flea beetles, which emerge a bit earlier. Planting fall broccoli or greens? Think twice before you put them close to your spring plantings - especially if you had a significant number of flea beetles. Those new adult beetles that will be emerging in August will be very hungry. If your fall brassicas are close by, feeding damage will be heavy. Try to rotate fall brassicas to a field that did not have spring brassicas.

OTHER PROBLEMS SEEN IN MAINE THIS WEEK

Let me know if these are big problems for you.

Onion thrips
Bacterial wilt of cucumbers, etc.
Squash bugs (and subsequent browning of leaves)
Early blight on tomatoes
Hopper burn caused by potato leaf hopper (I am trying to compile a list of resistant and susceptible varieties, e.g., red norlands go down very fast. Let me know what worked well of your potato varieties)

(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.)