Lep Monitoring Update WBC Numbers Increase, Scouting Expands

Western Bean Cutworm
Western bean cutworm (WBC) averages have increased in many counties across Ohio from July 18 - 24. For the week ending July 24, the statewide average was greater than 9 moths, an increase from the 8 moth average last week. We recommend that any counties that reported an average of 7 or more moths within a week should begin scouting for egg masses. Over the past week 14 counties reported an average of 7 or more moths including: Ashtabula, Coshocton, Defiance, Erie, Fulton, Geauga, Hancock, Huron, Lucas, Paulding, Portage, Sandusky, Trumbull, and Williams (Figure 1).

Western Bean Cutworm Moth Map
July 18 – 24, 2022
Figure 1. Average western bean cutworm (WBC) moths captured from July 18th through July 24th. The large number indicates the average moth count for the week and the small number in parentheses is the total traps set up in the county.

Scouting guidelines
1) Counties reporting an average of 7 or more moths within a week should scout for WBC egg masses (Figure 2).

2) Randomly choose 20 consecutive plants in 5 locations within a field (a total of 100 plants per field).

2) Inspect the uppermost 3–4 leaves of the corn plant. It is helpful to look at the leaves with the sun behind them. Oftentimes the shadow of the egg mass will show through the leaf without having to examine the leaf closely.

3) Record the number of plants with egg masses or larvae to calculate the percentage of plants with WBC present.

For more scouting information, view our WBC scouting video https://aginsects.osu.edu/news/western-bean-cutworm-video

Treatment Recommendations
Field corn should be treated with a foliar treatment if more than 5% of inspected plants have eggs or larvae. Sweet corn should be treated if more than 4% of inspected plants have eggs or larvae (processing market), or 1% of plants (fresh-market). Timing an insecticide application is critical and must happen before the caterpillar enters the ear, but after the eggs hatch. If the eggs have hatched, applications should be made after 95% of the field has tassels. If the eggs have not hatched, monitor the egg masses for the color change. When the egg masses are first laid they are a whiteish color. As the egg masses mature, they turn a purplish color. Hatch will occur within 24–48 hours once eggs turn purple.

Figure 2. A) Western bean cutworm egg mass on upper leaves of corn plant. B) Close up of WBC egg mass, pencil for scale.

Corn Earworm
The number of Corn Earworm (CEW) numbers remain low but did slightly increase this past week. Brown county numbers increased from last week and overtook Van Wert County as the highest out of all monitoring counties with an average of 7 moths (Figure 3). 

Corn Earworm Moth Map
July 18 – 24, 2022
Figure 3. Average corn earworm (CEW) moths captured from July 18th through July 24th. The large number indicates the average moth count for the week and the small number in parentheses is the total traps set up in the county.

Fall Armyworm
Of the 5 counties that are monitoring Fall Armyworm (FAW), 4 counties have reported catching FAW the week of July 18 – 24, an increase from only 2 last week. Clark reported the most FAW with 4, an overall decrease from their 6 last week (Figure 4).

Fall Armyworm moth map
July 18 – 24, 2022
Figure 4. Average fall armyworm (FAW) moths captured from July 18th through July 24th. The large number indicates the average moth count for the week and the small number in parentheses is the total traps set up in the county.

European Corn Borer
This week’s numbers for European Corn Borer (ECB) have remained steady with no counties reporting of finding any ECB for the second week in a row (Figure 5).

European Corn Borer Moth Map
July 18 - 24, 2022
Figure 5. Average European corn borer (ECB) moths captured from July 18th to July 24th. The first number indicates the average ECB-IA followed by a comma and then the average ECB-NY moth count for the week. The small number in parentheses is the total traps for each species set in each county.

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.