Lep Monitoring Update WBC Numbers on the Rise, Scouting Recommended

Western Bean Cutworm

Western bean cutworm (WBC) numbers have increased in many counties across Ohio from July 11 - 17. For the week ending July 17, averages were greater than 7 moths per week and scouting egg masses is recommended in Ashtabula, Defiance, Fulton, Huron, Lucas, Paulding, Sandusky, and Wood counties (Figure 1). Overall, the statewide average was 8.2 moths per trap (this is an increase from a statewide average of 1.0 moths per trap from July 4 – 10).

Western Bean Cutworm Moth Map
July 11 – 17, 2022

Figure 1. Average western bean cutworm (WBC) moths captured from July 11th through July 17th. 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.

WBC Scouting guidelines

Scouting for egg masses is recommended in counties with adult WBC trap counts averaging 7 or more moths per week, particularly in corn fields that are pre-tassel approaching tassel. Newly laid egg masses are white and laid on the uppermost 3 -4 leaves (Figure 2). As the egg masses mature, they turn a purplish color. Hatch will occur within 24–48 hours once eggs turn purple.

To scout for egg masses:

1) 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 making the egg mass easier to see.

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

WBC Treatment

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.

A close-up of a golf ball

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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 earworn (CEW) has decreased again this week. Van Wert county numbers have decreased from last week but are still the highest out of all monitoring counties with an average of 3.5. The total number of counties finding CEW has fallen to three, which include Van Wert, Madison, and Brown counties (Figure 3).

Corn Earworm Moth Map
July 11 – 17, 2022

Figure 3. Average corn earworm (CEW) moths captured from July 11th through July 17th. 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), 2 counties have reported catching FAW the week of July 11 – 17. Clark reported an average of 6, while Van Wert reported an average of 2.3 (Figure 4).

Fall Armyworm moth map
July 11 – 17, 2022

Figure 4. Average fall armyworm (FAW) moths captured from July 11th through July 17th. 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 decreased. No counties reported adult ECB from July 11 – 17 (Figure 5).

European Corn Borer Moth Map
July 11 - 17, 2022

Figure 5. Average European corn borer (ECB) moths captured from July 11th to July 17th. 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.