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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.

June 22, 2004

Eastern New York Cornell University Weed Day

Date:  Wednesday, JULY 7.

Where: CORNELL/VALATIE RESEARCH FARM, Valatie, NY (State Farm Road off Route 9 just north of Valatie)
Time: 9:30 a.m. Registration, 10:00 - 12:00 p.m. Field Crop Weed Control
Note: CCA and DEC Credits have been requested
Why Come: You can learn and see the newest strategies for controlling weeds in field corn!


Strange Happenings: Alfalfa Weevil

This year, while monitoring alfalfa weevil I have seen very few larvae reach the 4th instar. I kept waiting and this week there was not a single alfalfa weevil in the field. I looked for pupa all curled up in the leaves and found very few. I did see a lot of larvae infected with a fungal pathogen this growing season. The fungus is Zoophthora phytonomi and the epidemics it may cause are favored by wet conditions like those we have had this season. When weather conditions favor Zoophthora phytonomi it can kill about 60% of the larval population. This might be the reason why the alfalfa weevil infestations were low.

Beneficial Organisms: Damsel Bugs

Every year, I see many damsel bugs in the sweep net when monitoring alfalfa. Damsel bugs, also known as “nabids”, eat small insect eggs as well as aphids and mites. This insect uses a needle like mouth-part to insert into its prey and suck out the insides. They are slender, often yellowish-brown and about 8 -12 mm (3/8 to 1/2 inch) long. The wings lie flat across the back, crossing at the tips. The abdomen is slightly swollen and the body tapers toward a narrow, elongated head. The adult female inserts white colored eggs into the stem of the plant --only the egg cap shows. Damsel Bug nymphs are a little smaller than their parents but otherwise resemble wingless adults in shape and color. Be a little careful with damsel bugs because they are predators and can give a painful bite to big and small alike.

Potato Leafhopper Populations Remain Level

Talking with other extension educators this week has confirmed what I have also been seeing regarding PLH populations ­ they seem to be static, still well below action threshold.

Remember, potato leafhopper infestations can vary greatly from field to field. Checking all fields on a farm is important even if the first one you monitor might be below threshold. For management information check our on-line IPM guides: IPM for Potato Leafhopper in Alfalfa.

Field Corn
White Grubs Found in Fields

During a TAg meeting in Lewis County last week we discovered white grubs in corn fields. White grubs are the larval form of Japanese beetles, May or June beetles, or European chafers - all types of scarab beetles. White grubs are thick, white soft-bodied larvae about 1/4" to 1" long, and curl into a C-shape when disturbed. White grubs can be a problem in 1st year corn after sod, feeding on the roots of corn plants. Symptoms are gaps in corn rows at time of emergence and wilted, or stunted seedlings. There are no control measures for white grub. These insects are seldom an economically significant problem for corn in NY. For more information checkout our online publication: Early Season Field Corn Insect Pests

Stand Reductions by Early Season Corn Disease

Kevin Ganoe reports nearly 1/2 to 1/3 population reductions in some local corn stands. It may be too late to do anything about the problem now but highlights a possible management opportunity for next year, “Prevention is the key to control early season corn diseases!” By using a fungicide/insecticide planter box treatment will help prevent corn seed from many different early season diseases and seed corn maggot too. Sound planting practices, such as use of certified seed, good seed bed preparation, good seed soil contact, and appropriate planting depth, help promote stand establishment and help avoid seedling blights and emergence diseases. For more information checkout our online publication: http://www.nysipm.cornell.edu/publications/corn_dis.pdf

Weed of the Week: Common Ragweed is Resistant to What?

Walking through a few corn fields this week I found healthy populations of common ragweed. According to predicative models 100% of common ragweed have germinated and emerged in NYS. Common Ragweed (Ambrosia artemisiifolia) is a dicot weed in the Asteraceae family.  The interesting thing about this weed is that populations of it have been found to be resistant to triazine herbicides in New York. This does not, however, mean all the common ragweed we encounter is triazine herbicide resistant. It means that under certain management practices when triazine herbicides are used extensively there is the potential that some individual plants may survive. These survivors produce seed and a portion of that seed is also resistant, thus contributing to a triazine resistant ragweed seed bank. In other parts of the country some common ragweed populations have been found to be resistant to some acetolactate synthase (ALS) herbicides. It is important to use different families of herbicides each year to prevent your common ragweed from developing resistance to any one type of herbicide. Don’t forget there are other weed control options than using just herbicides alone; like using a combination of cultivation and just banding herbicide over the corn rows. The better stewards we are regarding pesticide selection and use the more likely we will have effective materials available when we need them.

Do you know any other weeds resistant to herbicides in NYS? (See next week’s report for the answer!)

Soybean Aphids Found in Western NYS

Soybean aphids have been reported on soybeans in Western NYS. The one field I have access to does not have soybean aphids yet. Soybean aphid (SBA) is the only aphid that attacks soybeans in the United States. This aphid is very small at a 1/16 of an inch long when fully grown and may be yellow to yellow-green in color. SBA have two black-tipped tail pipes or cornicles that can be seen easily under a hand lens. They tend to colonize and are found on the under side of the leaf. The threshold for soybean aphids is 250 or more per plant through the R4 stage. To make the best decision you should take an average aphid count from 20-30 plants per field. This threshold allows for about 7 days for treatment action. For more information on managing insect pests on soybean check out our on-line publication: Soybean Insect Pest Management Guide

Thanks to: Jeff Miller (Oneida County), Kevin Ganoe (Chenango, Fulton, Herkimer, Otsego, Montgomery and Schoharie Counties), Jennifer Beckman (Lewis County), Keith Waldron (NYS IPM) and Julie Stavisky (NYS IPM) for contributing to this week's report.

Ken Wise