Agronomic Crop Insect Scouting

David Owens, Extension Entomologist, owensd@udel.edu

Early Season Moth Activity
Many thanks to Haley Sater and Joanne Whalen for checking traps for us. Trap counts are as follows:

Early Season Insect Pest Control Thoughts
Stand establishment is one crop stage that needs to be monitored like a hawk. We have waited a full year to plant again, we need to make sure our practices are dialed in and not ruined or damaged by an insect or slug. This year especially, with prices the way they are, we need to make sure that our pest management investment is well placed. Complicating this is that pest problems are very sporadic.

Let’s first take a look at corn. The vast majority of corn has a neonicotinoid seed treatment. The low rate should provide adequate protection against seedcorn maggot and aphids (rare but happens). White grubs and wireworms however are much tougher. You can scout for them by digging 8”x8”x6” holes, but I don’t know anyone who does. Mid to high rates of neonic seed treatment can provide good control of both. If you have a low rate of the seed treatment and planting into a field that has had issues in the past with either, you can also include a pyrethroid at planting in the furrow. A number of years ago I was at a field that had a heavy wireworm population (2-5 per hole). One half of the field was planted into Poncho250 and the other half of the field into Poncho500. The difference between the two in terms of wireworm damage was minor. It is not worth putting an in-furrow material on the 1250 rate. The next seedling pest of concern is cutworm. If planting in late-terminated cover crop or broadleaf winter annual weeds, there is a chance that they may be present. This is a critter that we can scout for as the plants emerge. We have thresholds for them. Take a look at the bag tag and the Handy Bt Trait Table (https://www.texasinsects.org/uploads/4/9/3/0/49304017/bttraittable_march2025.pdf). Some trait packages are effective on cutworm (most are not). If growing organic field corn, reduced tillage should help with at least avoiding seedcorn maggot. Delaying planting until closer to the end of the month is also a possibility as white grubs would have cycled out by then.

Soybean production is probably the most complex. No-till full season beans are at some risk of slug injury (although I suspect that the risk this year is very low). If cover crop is aggressively tilled into the soil, the field may be at risk for seedcorn magot. This is the ONLY scenario for which an insecticide seed treatment might not be a bad thing. Seed treatments and broadcast pyrethroid use at burndown or other soybean growth stage can result in a reduced population of ground beetles which would have helped eat slugs.

Later planting, late terminated cover crop are at greater risk for cutworm, but remember, cutworm are sporadic things, and soybean can take heavy stand loss and still compensate well. It is highly unusual for bean leaf beetle populations to be heavy enough to warrant an insecticide treatment.

Fields at risk for slugs can be planted later when soils are warm to promote rapid growth. A light tillage, strip tillage, or conservation tillage in combination with row cleaners should help mitigate slug impact. Last of all, baits can be applied, but they are expensive and for soybean, should be used no later than once the first beans crack through the soil.

On corn or beans, the most tempting practice might be to include an insecticide with herbicide burndown application, but this is also the BEST way to save money on input by EXCLUDING the insecticide. Instead, if a field has some risk for cutworm, scout the emerging bean plants for signs of stand impact.