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Sweet Corn Pheromone Trap Network for Western New York,
This is a seasonal scouting report giving growers in the Western New York area information on the presence of sweet corn pests and recommendations on scouting and thresholds. The report is written by Abby Seaman, NYS IPM's Area Extension Educator for Vegetables.
ECB-E catches are mostly down from last week. ECB-Z catches are mostly lower than last week, but higher at a few locations. One lone CEW caught in Eden. Some of the earliest fields are not over threshold for larvae in the tassel, which is unusual. In one silk stage field tiny ECB larvae are being found in the silks after hatching from eggs laid on the flag leaves. Any egg masses in the field during the next few days will be developing and hatching very quickly with the warm temperatures.
Watch for common armyworm migrating from small grain fields into corn and other vegetable crops. I've heard about them marching across roads in large numbers, and infesting peppers, strawberries, and lawns in addition to corn. If they are a problem in sweet corn, the 15% infested plants threshold applies for pre-tassel corn, and 5% for silking corn. Scout fields even if they are not at the tassel emergence stage, especially if small grain or grass cover crop or hay fields are nearby.
Corn should be first scouted for ECB at early tassel emergence. Even at a location with high ECB populations, insecticide applications to whorl stage corn did not result in improved control when compared with one or two well-timed applications at tassel emergence. Larvae feeding in the whorl are protected from insecticide applications and mortality will not be as high as at tassel emergence, when larvae feeding in the emerging whorl are exposed to the spray. Larvae will leave the tassel as it opens up and no longer provides a moist, protected feeding environment, and move down the plant looking for protected places to feed. Insecticide applications need to be timed to kill larvae before they bore into a new feeding location where they will be again protected from sprays. In fields with uneven development, two applications may be necessary, one when approximately 25-50% if the tassels have emerged, and again after 75% of the tassels have emerged, if the field is still over threshold.
The threshold for ECB at tassel emergence is 15% infested plants. Look down into emerging tassels for tiny larvae or frass (white to brown material about the size of fine sand). Before any insecticides have been applied, scouting is fast and easy because any sign of feeding is an almost sure sign of live larvae, so it's not necessary to spend time finding the larvae. After the initial insecticide application, feeding damage may be from a larva that has already been killed, so finding the critter is more important for an accurate count.
Once a field is silking, the threshold drops to 5% infested plants. Scout the ear zone (roughly from two leaves above and one leaf below the ears) for egg masses and larvae. Egg masses are found most frequently on the underside of leaves near the midrib, and consist of approximately 10-20 flattened eggs overlapping like fish scales. Eggs are white when first laid, turning cream colored after a couple of days, and showing the black head capsules of the tiny larvae through the surface of the eggs when within 1 day of hatching (the "black head" stage). Egg masses can also sometimes be found on the flag leaves of the ears or on the husk itself. Eggs take approximately 100 base 50 degree days to hatch. When temperatures are in the 70's during the day and the 50's at night egg masses will take about a week to hatch. When temperatures are in the 80's during the day and the 60's at night, they could take only 4 days to hatch.
Look down into the tops of the silks for newly hatched larvae, and pull the ear away from the stalk slightly to look for larvae feeding there.
The numbers below are the weekly total for each location.