Western Bean Cutworm Numbers Starting to Increase

Western bean cutworm moth

We are in the third week of monitoring for Western bean cutworm (WBC) in Ohio. Numbers of WBC moths doubled from the previous week; however, overall numbers across the state remain low. Trap counts for the week of July 6 – 12 resulted in a total of 117 WBC adults (1.3 average moths per trap) (Figure 1). A total of 27 counties monitored 91 traps across Ohio. Sandusky County reported capturing more than 1 moth / day over the 7-day monitoring period; therefore, scouting for egg masses should begin in this county. Fulton County is approaching scouting threshold. All other counties monitored remain below threshold.   

Figure 1. Average Western bean cutworm adult per trap followed by total number of traps in the county in parentheses for week ending July 12, 2020. 

Scouting guidelines

Figure 2. Western bean cutworm egg massScout pre-tassel corn approaching tassel fields. Choose at least 20 consecutive plants in 5 random locations (scout different areas of the field that may be in different growth stages). Inspect the uppermost 3–4 leaves. Consider treatment if >8% of inspected plants have eggs or larvae (field corn) or in sweet corn, if >4% of inspected plants have eggs or larvae (processing market), or >1% of plants (fresh-market).

Treatment

If the number of egg masses/larvae observed exceed threshold, many insecticides are available to adequately control WBC, especially those containing a pyrethroid. However, as with any ear-burrowing caterpillar pest, timing is critical. Insecticide applications must occur after egg hatch, or after tassel emergence, but before caterpillars enter the ear. If eggs have hatched, applications should be made after 95% of the field has tassel. If eggs have not hatched, monitor for the color change. Hatch will occur within 24–48 hours once eggs turn purple. To search for larval injury after it has occurred, search the corn for ears having feeding holes on the outside of the husks.              

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.