Corn Earworms In Soybean Are Active

PRINCETON, KY.
   Corn ear worm (CEW), also known as soybean podworm, are currently active in soybeans. This is a direct damage pest as it feeds on pods, seeds, & petioles. You are unlikely to detect this pest by checking for defoliation because it does not feed much on leaves. There is no sure way to detect this pest in your soybean crop except to scout for it. This means sweeping or direct visual examination of the pods.
   CEW may occur in many color phases. It sometimes appears very dark, almost black, to brown to red and green. The green color phase is most often seen when feeding in soybeans. When fully grown, the larvae are about 1 ½“ long. They are marked by alternating light and dark stripes running the entire length of the body. These stripes are not always the same from one caterpillar to another. Usually a double dark stripe will run down the middle of the back.
   You can certainly look for direct damage feeding on the pods to see if they are causing damage. In rows narrower than 30”, sweeping with a 15” sweep net is about the only way to measure this pest. The threshold is 9 worms per 25 sweeps.
   We do know that corn earworm moth flight has been increasing and populations are greater than we normally see. Moth capture in our IPM pheromone baited traps at the UK-REC in Princeton is shown in Figure 3. Remember, these are moth counts and moths are NOT the damaging stage. Caterpillars will appear about a week after the moth flight. In 2012, moth numbers (green line) are greater than the rolling five- year average (blue line) so we are at an elevated risk of damage from this pest compared to most years. However, trap captures will NOT tell you what will happen in an individual field.
   Only field sampling will help you establish whether or not a threshold has been met. Moth flight numbers will give you a week or two heads up on what might happen. 
   If insecticide control is warranted, you may find products listed for control of CEW in soybeans online at: http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html or from your County Extension Office. Be wary of spraying too early, you may kill the predatory insects that are providing some natural control and miss the actual pest. Δ
   DR. DOUG JOHNSON: Extension Entomologist, University of Kentucky

Figure 2. Corn earwormin the green color phase commonly seen in soybeans.

Figure 3. Capture of corn earworm moths in IPM pheromone baited traps at UK-REC, Princeton (Caldwell Co.) KY in 2012.