Issue No. 6, Article 3/April 30, 2004
Intense Captures of Black Cutworm Moths
April showers have brought us not only spring flowers but also black cutworms. Many cooperators monitoring sticky traps in Illinois are beginning to report cutworms on a regular basis. Cooperators in several counties have reported intense captures during the week of April 26. Just a reminder: an intense capture is a cumulative total of nine or more moths caught over 2 consecutive days.
After an intense capture is recorded, we can calculate degree-days to project when black cutworm injury, specifically cutting of corn plants, will occur. Table 2 lists counties in which intense captures of black cutworm moths have been recorded and the expected dates when cutting by black cutworm larvae will occur.
Jim Morrison, Extension educator in crop systems in Rockford, reported that no intense captures have been recorded from the four traps for which he is coordinating reports for northern Illinois (located near Baileyville, Freeport, Milledgeville, and Winnebago). However, a few black cutworm moths have been captured in the traps near Baileyville and Winnebago.
Ron Hines, senior research specialist at the University of Illinois Dixon Springs Agricultural Center, indicated that more intense captures of black cutworm moths occurred in his traps in southern Illinois during the week ending April 27. Moth captures have been particularly numerous in the traps in St. Clair and Pulaski counties (http://www.ipm.uiuc.edu/pubs/hines_report/index.html). Ron also reported that "rescue" applications of insecticides to prevent excessive cutting injury already have begun in some of the southern counties. Based on degree-day projections using the degree-day calculator at http://www.ipm.uiuc.edu/degreedays/index.html, cutting is right on time in that area.
We encourage you to scout cornfields in your area for black cutworm injury. The recent cooler temperatures should have slowed down development of black cutworms in some areas, but it's better to be safe than sorry. A lot of early-planted corn should escape serious cutworm damage, but keep your eyes on the seedlings as they emerge.
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 that this threshold should be changed. 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).
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.
Insecticides suggested as "rescue" treatments for control of black cutworms are shown in Table 3. If an insecticide application is warranted, please follow all label directions and precautions.--Kevin Steffey and Kelly Cook