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Eastern New York Field Crops Pest Report, 2004

This is a seasonal scouting report giving growers in the Eastern New York area information on the presence of agricultural pests. The report is written by Ken Wise, IPM Extension Area Educator for Livestock and Field Crops.

August 26, 2004

SOYBEANS

Downy Mildew Found on Leafs

At the Cornell University Research Farm in Valatie (Columbia County) this week I found soybean plants with downy mildew. Early symptoms of this disease appear as pale green to light yellow spots on the leaves. As downy mildew progresses the lesions increase in size and turn pale to light yellow. When leaves become severely infected they turn yellow, brown, curl around the edges and drop off prematurely. The soybean pod may also become infected, but there are no symptoms on the outer surface. The pod may have a white moldy fungus in the interior surface and may infect the seed. Oospores survive within leaf residue or in seed. Cool to mild temperatures and high humidity favor this disease. Management of downy mildew can be accomplished by crop rotation and clean tillage of fields with infested residue. There are also some soybean varieties that are resistant to downy mildew.

FIELD CORN

Deer and Bird Damaged Corn Ears: Open the Door

This week I have seen an excess of corn ear damage created by deer and birds. The husk covering the corn was pulled back and about a third of the grain was gone. Some of the ends of the ears were bitten right off by deer. In addition, the open husk can allow a variety of diseases to infect the ear of corn. Some of these diseases might be: Common smut, Fusarium ear rot, Gibberella ear rot, Diplodia ear rot, Cladosporium ear and kernel rot, and more.

For more information on diseases that infect the corn ear, see next weeks report!

European corn borer and Corn Standability

European corn borer (ECB) damage can on occasion cause localized problems for field corn producers. However, while ECB damage may be conspicuous, it more typically does not cause significant economic losses in NYS. As you may know, ECB can drill holes in corn stalks thus, causing them to weaken. Harvest yield loss is greatest with weak-stemmed hybrids and increases when late harvesting and/or adverse weather leading to more lodging in the field. If you tend to have this problem with lodging corn you should consider selecting corn hybrids with strong standability (strong-stemmed). These hybrids can withstand more ECB damage and keep standing.

ALFALFA

What is an Alfalfa Snout Beetle: Identification, Lifecycle and Signs of Damage

Alfalfa snout beetle (ASB) is a very serious root-feeding weevil that is found only in northern New York State and southern Ontario. Adult ASB feed on leaves and stems, and the larvae feed on the roots of alfalfa and clover. ASB is one of the few pests that can completely destroy an alfalfa field. Some growers have been forced to grow other forages than alfalfa because of the destructive damage by this insect to alfalfa and certain clovers. Adult ASB are mottled gray, humpbacked, 1/2 inch long, do not fly, and are all females. Adult ASB emerges in the spring to feed on new shoots from the alfalfa crown. (Note: above ground active adult ASB is only a small portion of the infestation). ASB lives under the soil surface for about 2 years. When adults emerge in the spring they migrate in mass numbers often in a northeast or northwest direction. Legless white larvae, are a 1/2 inch long, can be found within a foot of the soil surface in mid to late summer and feeding on alfalfa roots. Larvae feed on side roots, and girdle the main taproot causing death to the plant. ASB root feeding and systemic root diseases can cause alfalfa stands to exhibit signs of early senescence in the fall. In counties with confirmed ASB infestations, fields showing these symptoms should be sampled for ASB. If snout beetles are present their larvae should be easily found on alfalfa tap roots. THIS MEANS CHECK NOW! During late summer and early fall the larvae move deeper in the soil where they spend the winter. The following spring the larvae move 10-12 inches from the surface, pupate by mid-summer and become inactive adults, which remain in the soil until the following spring. To combat the ASB the only line of defense is to practice intensive crop management. Rotation with susceptible and non-susceptible crops is very important. Rotation limits the ASB from developing large infestations in field. ASB has host plants other than alfalfa that make eradication impossible. Host plants for ASB are: alfalfa, red clover, dock, wild carrot, quackgrass, and white clover. Non-host cultivated crops for ASB are: corn, wheat, oats, soybeans, potatoes, and birdsfoot trefoil. Growers should plan to crop alfalfa for 2 to 3 seasons, using clear seedlings, and then rotate with non-host cultivated crops for 2 or 3 successive years. New infestations can be caused by transporting ASB to other farms, fields or homes. Take precautions to limit artificial transport of ASB by cleaning equipment between fields and farms. Limit transporting possible infested hay bales, gravel and soil to non-infested sites. Research is continuing to identify sources of alfalfa root resistance to ASB (Don Viands, Julie Hansen and Elson Shields). The use of an insecticide for the control of this insect has not been shown to be effective.

Where do potato leafhoppers go in the fall?
In late summer and early fall, potato leafhoppers migrate back to the southern United States. Potato leafhoppers over-winter on pines and numerous other host plants in the southern and southeastern United States. For more information, see Potato Leafhopper on Alfalfa Management Guide

Thanks to: Keith Waldron and Julie Stavisky (NYS IPM) for contributing to this week's report.

Cheers,
Ken Wise