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Eastern New York Field Crops Pest Report, 2002

For 5/24/02:

Alfalfa

Alfalfa at the SUNY Cobleskill farm was 14 to 24 inches tall although most of it has lodged (May 21).

Alfalfa Weevil: A good control measure for alfalfa weevil is your 1st cutting of alfalfa. Wet weather may delay harvest and this might allow alfalfa weevil to reach levels that can cause economic damage. It is still essential to scout for alfalfa weevil even if you canít get in the fields to harvest. The reason is when fields do become dry enough to harvest you can cut the alfalfa that is closest to the tip feeding threshold first, avoiding more yield losses. Alfalfa weevil threshold before first cutting is 40% tip feeding. Sometimes harvesting alfalfa will not totally control alfalfa weevil and you can still get economic damage on re-growth. Insecticide use may be necessary after the first cutting if small larvae are still present and damaging growth of at least 50% of the new buds. Watch windrows for signs of weevil feeding on regrowth.

Recent rains may have helped us a bit by fostering conditions favorable to epidemics of a fungal disease (Zoopthora spp.) which attacks alfalfa weevil - and other insects. If you see shriveled up, brown colored, or dead weevil larvae you know fungal diseases are at work keeping alfalfa weevil populations low.

SUNY Cobleskill alfalfa fields are currently at 0% 45% tip feeding with many larvae ranging from 1/8 to 1/2 inch long. Out of 10 alfalfa fields monitored, only one 3rd year field was over threshold for alfalfa weevil this week (May 21).

Terry Lavigne (Albany County) reports 15% to 30% tip feeding with many small larvae in the alfalfa fields (May 23).

Kathryn Chabarek (Dutchess and Columbia County) reports 5% to 95% tip feeding on several farms. Many farms are in the progress of their 1st cutting of alfalfa. She observed one alfalfa field at extremely high tip feeding (95%) levels. This field will be harvested this week (May 21).

Check out our on-line publication, IPM for Alfalfa Weevil. 1.2 Mb pdf file

Potato Leafhopper: The season for potato leafhopper is closing in quickly. So, it is time to dust off that sweep net you have in the closet and start looking of potato leafhopper. If you canít remember what they look like, adults are bright lime green, 1/8 inch long and can fly. Potato leafhopper nymphs are yellowish-green and look similar to the adult but do not have wings.

Check out our on-line publication, Potato Leafhopper Management in Alfalfa

Alfalfa Disease: Verticillium. Kathryn Chabarek (Dutchess and Columbia County) reports verticillium infected plants in an old stand of alfalfa (May 21). Verticillium wilt can be a serious disease limiting yield and the number of productive years of an alfalfa stand. An early symptom includes V-shaped discoloration at the tip of a leaflet. As the disease progresses, leaflets wilt, turn yellow or pink, and often curl or twist. The curl and twisting of leaflets is the most characteristic symptoms of Verticillium wilt. Taproots appear healthy and sound, but have a dark ring (the water-conducting tissues) which is evident when the taproot is cut in cross section. Verticillium wilt symptoms may be more obvious in the second cutting.

Check out our on-line publication, Verticillium Wilt in Alfalfa, (1.3 Mb pdf file).

Grass & Pasture

Grasses at the SUNY Cobleskill farm range for 10 to 20 inches tall, but has lodged due to wind, rain and snow.

White Grubs: Pete Carey (Sullivan County) reports an infestation of 10 white grubs per square foot in a pasture (May 17). White grubs are the larval forms of Japanese beetles, May or June beetles, Oriental beetles or European chafers. White grubs are thick, white soft-bodied larvae about 1/4" to 1" long, and curl into a C-shape when disturbed. White grubs feed on the roots of grasses in pastures and hay fields. White grubs can also be a problem in 1st year field corn after sod. Crop rotation is the most effective control method for white grubs in pasture.

True Armyworm: Lisa Fields, (Schoharie County) and Kevin Ganoe (Chenango, Fulton, Herkimer, Montgomery and Otsego Counties) reports very low armyworm moth counts this season.

Grass Diseases: Aaron Gabriel, (Washington County) and Rebecca Bennett (Cornell graduate student) have identified an orchard grass disease called Cercosporidium graminicola. The disease is favors prolonged cool, wet weather in April and May.

Field Corn

Kathryn Chabarek (Dutchess and Columbia County) reports that field corn is at the 1st and 2nd leaf stage.

Corn Rootworm and Wet Soils: Should a grower treat a corn field for corn rootworm (CRW) if it was over threshold last year and has flooded?

CRW eggs are resilient to wet, dry and cold weather conditions. Because CRW eggs will not hatch for several more weeks they most likely will survive. Appearance of fire flies signal the approximate time of CRW egg hatch. If a field floods when larvae are present it may cause some mortality. So the question is fHow much mortality? This is tough to predict. It would be a gamble not to treat the field if it was over threshold the previous year.

Crows in Field Corn: There has been a lot of discussion on what to do about crows in field corn. Recommendations are limited. Propane cannons may provide some relief, however crows can adapt to the sound and one should consider community relations when installing a source of regular Ka-Booms. Other suggestions include paying close attention to planter settings for depth and seed slot closure, planting at a higher population on fields where bird feeding is anticipated, setting out alternative or decoy foods for birds such as moistened corn seed.

Weeds in Field Corn: In several of the corn fields at SUNY Cobleskill, 1000s of wild mustard seedlings are starting to appear. In some areas of the field there are 50+ per square foot.

Have a good Memorial Day weekend!