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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 4, 2004
Fungus Killing Alfalfa Weevil?
During wet springs with high relative humidity a fungus aids in reducing alfalfa weevil infestations. I observed alfalfa weevil larvae infected with the fungus Zoophthora phytonomi. Infected larvae slowly turn a pale cream color and dies. When conditions favor Zoophthora phytonomi it can kill about 60% of the larval population.
Other parts of the US Armyworms are present
In the Mid-West common armyworm has damaged corn and some wheat fields. We have not seen any damage here in NYS as of this week. It is always good to keep a keen eye on your corn, wheat, oats and grass fields for armyworm. True armyworm larvae appear smooth, cylindrical, pale green to brownish when they are still small. Mature larvae are smooth and marked with two orange, white-bordered strips on each side. True armyworms range in size from 1/8 inch to 1.5 inches long. It is important to detect armyworm areas early, while larvae are still small, since large larvae do most of the feeding and quickly destroy whole stands of corn, grasses and small grains. Because armyworms feed at night look for chewed leaves, cut stems, lodged plants, pellet-like frass on the ground, and larvae hidden under plant canopy and surface residue. You will need to be aware that armyworms can move from field to field every quickly. Start scouting for the armyworms in May and repeat scouting every 3 days to 5 days. Monitor fields for armyworm larvae when they are less than 1/2 inch long. If there are sufficient numbers and damage is present, an insecticide could be justified. Treat only the affected area and a 20 to 40-foot border around the infestation. Rarely does a whole field need to be treated for armyworm. Larger armyworm larvae, greater than 1/2 inch long, are much more difficult to control. These large larvae are more tolerant of insecticides, reducing the effectiveness and economic viability of this option.
Japanese beetle and Mexican bean beetle are the main defoliators of soybeans in NYS. While they are minor pests, defoliation of soybeans sends up many red flags by growers. The question normally is how much leaf defoliation is too much in soybeans? The good thing is that soybeans can withstand much defoliation without losing yield. The soybean defoliation threshold is 35 percent of leaf eaten or missing V1 to just before bloom. During blooming through pod-filling stages, the threshold is 20 percent defoliation. The following pictures are a guide that depict 10, 20, 30 and 40 percent defoliation:
(Source: Purdue University Field Crops Pest Management Manual, 1/92)
For more information
on managing insect pests on soybeans, check out our on-line publication:
Pest Management Guide
What are the early season diseases that can infect soybeans? See next weekís report for enlightenment!
While at the Cornell Musgrave Research Farm last week we observed cereal leaf beetle on wheat. Even if we have not seen this pest in Eastern NYS yet it is important to know what it looks like. Here is a photograph Keith Waldron snapped of eggs and a larva of cereal leaf beetle:
Thanks to: Jeff Miller (Oneida County) Keith Waldron
(NYS IPM) and Julie Stavisky (NYS IPM) for contributing to this