Sweet Corn Pheromone Trap Network for Western New York, 2002

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.

For 6/18/02

The trend in ECB trap catches is generally upward, with both E catches mixed and Z race catches up at most locations this week. Egg masses and newly hatched larvae are being found in fields. Keep an eye on small plants in fields with Stewart's wilt susceptible varieties. Some fields have had a lot of feeding. The threshold for foliar applications against corn flea beetle is 6 beetles on 100 plants.

Fields at the most advanced stage of development will be most attractive to egg-laying ECB moths. Larvae hatching from eggs laid now will feed in the whorl and be found later in the emerging tassel. Information from North Carolina indicates that CEW will lay eggs on the growing tips of small corn plants, and larvae will feed on the whorl. The feeding sounds similar to FAW feeding, and any CEW larvae can probably be targeted in a tassel emergence spray.

Corn should be first scouted for ECB, armyworms, and CEW larvae where they are being caught 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 tassel 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 and armyworms at tassel emergence is 15% infested plants. For corn borers, look down into emerging tassels for tiny larvae or frass (white to brown material about the size of fine sand). For armyworms look for ragged feeding holes and frass pellets the texture of coarse sawdust. The North Carolina web page cited above describes CEW whorl feeding as follows: numerous ragged holes appear when the blades unfurl. Wet, tan to brown excrement lodges in the whorl and blade axils. This condition is often referred to as "shatterworm" injury.
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 estimate of the number of infested plants.

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