No. 5 Article 2/April 22, 2005

First Intense Capture of Black Cutworm Moths

Black cutworm flights continue across the state this week. The first intense capture of black cutworm moths has occurred (9 or more cumulative moths caught over 2 consecutive days). Marc Rigg, with Pioneer in Good Hope, reported an intense capture on April 12 and 13 in his trap on the Mason-Tazewell county line.

After an intense capture is recorded, we can calculate degree-days to project when black cutworm injury, specifically cutting of corn plants, will occur. Black cutworm larvae are expected to begin feeding on and cutting corn plants with the accumulation of approximately 300 degree-days (base 50°F) after an intense capture occurs. We project the cutting of corn plants to occur between May 14 and May 16 near Mason and Tazewell counties. Remember, if you are monitoring a pheromone trap, you can predict cutting dates in your area by using the Degree-Day Calculator on the IPM (http://www.ipm.uiuc.edu/degreedays/) and WARM (http://www.sws.uiuc.edu/warm/pestdata/) Web sites.

As corn continues to emerge across the state, we encourage you to scout cornfields in your area for black cutworm injury. Small larvae will feed on corn plants, causing small, irregular holes in the plant leaves. Larvae begin cutting plants when they reach the fourth instar. Feeding primarily at night, larvae will move up the row as they feed. Large sections of fields may be quickly destroyed before the injury is noticed. On average, one larva may cut an average of three or four plants in its lifetime.

For years, the rule-of-thumb treatment guideline for black cutworm injury has been 3% to 5% cutting. No more recent data have been gathered to suggest a change. However, you can judge the severity of damage and the possible need for an insecticide based on the location of the cut (above or below the growing point), the size of the cutworms, and the soil conditions (moist or dry). Plants cut above ground will recover, to a certain extent; plants cut below the growing point will not recover. Younger cutworms (third and fourth instars) will cut more plants over time than older cutworms (fifth and sixth instars). For more information on black cutworm injury, scouting, and management, please see our black cutworm factsheet (Adobe PDF).

Suggested rescue treatments for black cutworm are summarized from the 2005 Illinois Agricultural Pest Management Handbook and listed in Table 1.


Corn injury caused by black cutworm feeding.


Photograph of a head capsule gauge (not to scale) showing two different black cutworm instars, approximate days left to feed, and potential number of plants that may be cut.

--Kelly Cook

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