Sweet corn pheromone trap catches: What do they mean? How do I use them?

The New York State Integrated Pest Management Program, along with many collaborators, operates a network of pheromone traps in western and central NY. These numbers appear, along with interpretation, in the Veg Edge weekly pest update. But what do these numbers mean and how are they used when making a decision to spray or not to spray a field?

We trap for European corn borer, fall armyworm, western bean cutworm, and corn earworm. Only the corn earworm trap catches are used directly to make a spray decision. Trap catches for the other pests are only one piece of information to make a spray decision. Scouting and thresholds are the primary means of deciding if and when to spray.

European corn borer and fall armyworm:
Trap catches are useful as a backup to scouting. If you scout a field and find it’s under threshold, and the trap counts are low, you can feel pretty sure that a spray is not needed. If trap catches are high and you’re not finding anything, maybe you need a scouting refresher course to be sure you’re able to see egg masses and damage. Remember that damage may be caused by larvae hatching earlier in the season when trap catches were high, even though they are not currently high. Another thing we’ve observed is that in hot, dry seasons moths may not lay as many eggs as we would expect because they don’t have access to water, so high trap catches are not always an indicator of what’s happening in the field. That’s why scouting is more reliable.

Western bean cutworm: trap catches are used as an indicator of when to scout for egg masses. Western bean cutworm only has one generation per year, so when the flight has peaked, fields in the late whorl – green silk stage should be scouted for egg masses, and if over threshold, sprays should be timed to prevent larvae from tunneling into ears.

Corn earworm: Because corn earworm moths lay their eggs directly on silks and they are difficult to reliable scout for, we use trap numbers to determine how often to spray green silk stage corn. The higher the trap catches, the more frequently the field needs to be sprayed.