The western bean cutworm has slowly but steadily been advancing into Ohio from the western USA over the past 10 years. It is still at low density at most sites in northwestern and northeastern Ohio, and not yet detected at some southern Ohio sites, but growers should be aware of its possible presence in sweet corn fields. This caterpillar feeds on kernels of ears in both sweet corn and field corn. Feeding damage is usually at the tip end but can be in the middle or butt end of the ear. The western bean cutworm can be found as several larvae per ear, because it is not cannibalistic; this makes it different than the corn earworm, which also feeds on kernels at the tip of the ear, but which typically is found as a single larva per ear because it cannibalizes other corn earworm larvae.
The newer BT sweet corn hybrids in the Attribute II series (from Syngenta) provide genetic control of the western bean cutworm, but BT sweet corn hybrids in the Performance series (from Seminis) and the older Attribute series (from Syngenta) do not control this pest.
Monitoring of western bean cutworm is a two-part process. First, the adult moths can be monitored with a pheromone trap using a commercially available lure that lasts for 4 weeks. A bucket type of universal moth trap can be used, or a trap can be made from a one-gallon plastic milk jug with part of the sides removed, with an inch of dilute antifreeze solution in the bottom as a drowning and preserving agent. This pest has one generation per year, with adults usually first detected in late June, peak activity in late July, and moth activity ending by late August. Trap reports on western bean cutworm from several Ohio locations can be found using this link: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=441280294
On any farm where the western bean cutworm moth is detected in traps, scouting should be done to monitor eggs and hatching larvae. Scouting should concentrate on plantings in the emerging-tassel stage. Look at 20 consecutive plants in each of 5 random locations per field. Examine the flag leaf, where eggs are usually laid. Eggs are laid in masses. Eggs are white when fresh, then they darken to purple when ready to hatch. Hatch will occur within 24-48 hours once eggs turn purple. Our tentative threshold for sweet corn is to consider treatment if eggs or larvae are found on more than 1% of plants for fresh-market or on more than 4% of plants for the processing market. Insecticide applications must occur after egg hatch, or after tassel emergence, but before larvae enter the ear.
Pictures and additional details on western bean cutworm can be found in our OSU fact sheet: