Missouri Corn Growers Alerted to Black Cutworm Threat

By Blake Jackson

University of Missouri Integrated Pest Management has issued its initial pest alerts for the growing season, urging corn and wheat producers to monitor for early threats like Black cutworm and True armyworm.

MU Extension entomologist Ivair Valmorbida reports significant Black cutworm moth activity in some areas, with predicted damage appearing around the first week of May in Missouri.

This "cut date" is an estimate based on temperature data. Extension specialists across the state track pest numbers using traps, and subscribers to the IPM Pest Monitoring Network receive text alerts when thresholds are exceeded.

Black cutworms are migratory pests arriving from the Gulf Coast or Mexico. In corn, their larvae damage seedlings by cutting them at or below the soil surface, often dragging the plant into burrows in dry conditions.

Valmorbida advises scouting for larvae after corn emergence, examining 25 plants in ten different field locations every 7-10 days until the V4-V5 growth stage.

Treatment thresholds vary rescue insecticide is suggested when 2-4% of seedlings are cut belowground or 6-8% show aboveground feeding or cutting.

Valmorbida also emphasizes the cost-effectiveness of scouting for True armyworm, which affects wheat, corn, and forage grasses.

Scouting methods and treatment thresholds differ for each crop. Armyworm larvae feed from leaf edges towards the midrib, typically feeding early morning or near dusk.

In wheat and forage grasses, larvae primarily consume leaves but can also clip wheat heads, causing significant yield loss. The treatment threshold for these crops is an average of four larvae per square foot.

However, larvae over one inch long can be disregarded as they are nearing pupation. Due to the severity of head clipping in wheat, insecticide application is recommended if 2% of heads are clipped and larvae are present. Growers are encouraged to stay vigilant and utilize scouting to make informed pest management decisions.

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