University of Illinois

No. 5/April 24, 1998

Black Cutworm Moth Flight Continues, But Reported Intense Captures Subside

Volunteers who have placed sticky pheromone traps in several areas of the state to capture black cutworm adult males continue to report their captures on a relatively regular basis. We sincerely appreciate receiving this information, which helps others in Illinois who are interested in the continuing activity of black cutworms. In articles in forthcoming issues of this Bulletin, we will provide dates of intense captures of black cutworm moths (nine or more moths captured during a 1- to 2-day period) and project when cutting activity of larvae commences (accumulation of heat units above a base temperature of 50 degrees F after an intense capture).

After the surge of black cutworm adult males captured in pheromone traps between April 8 and 13, the numbers of moths captured subsided in some areas of the state. Jeff Staly, who is monitoring three traps near Ridgway in Gallatin County (Southeast Crop-Reporting District), captured 17 and 27 male black cutworm adults in two traps during the period April 14 and 15, and 10 moths on April 19, but captures on April 21 were quite low. Kevin Black, who is monitoring a trap for Cargill Hybrid Seeds near Lexington in McLean County (Central Crop-Reporting District), captured 11, 13, 13, 18, and 12 black cutworm moths on April 6, 7, 13, 17, and 20, respectively. Doug Gucker, with United Prairie Co-op in Piatt County (East Crop-Reporting District), captured 11 black cutworm moths on April 15. Although David Feltes, Extension IPM educator in the Quad Cities, and Jim Morrison, Extension crop systems educator in Freeport, have been catching black cutworm males in their traps in the Northwest Crop-Reporting District, neither has observed an intense capture for a while.

From the aforementioned intense capture of black cutworm moths and from intense captures reported in earlier issues of this Bulletin, Bob Scott with the Illinois State Water Survey has been able to project accumulations of 300 heat units above a base temperature of 50 degrees F. The dates on which these projected accumulations of heat units might occur are presented in Table 1. To interpret the information in the table, choose the location nearest you,then look in the column under a selected date of an intense capture for the projected date on which initial cutting activity by fourth-instar black cutworms might occur. For example, from an intense capture near Carbondale on March 30, initial cutting activity by fourth-instar black cutworms could begin as soon as April 29. From an intense capture near Peoria on April 9, initial cutting activity by fourth-instar black cutworms could begin by May 15.

Table 1. Projected date when 300 heat units above base 50 degrees F will have accumulated after the date of an intense capture of black cutworm adults (nine or more moths caught in a pheromone trap during a 1- to 2-day period).

Crop-reporting district and locationDate of intense capture of black cutworm adults in pheromone-baited traps
Projected date of cutting activity by black cutworm larvae
Rend Lake4/224/224/234/234/234/254/305/45/45/55/75/8
Dixon Springs4/214/214/224/224/224/244/305/35/35/45/65/7
West Southwest
Wildlife Park5/45/45/55/55/55/75/115/135/135/145/155/16
St. Charles5/105/105/105/105/105/125/155/185/185/195/195/21

As soon as corn gets planted and begins to emerge in southern Illinois, cutting injury caused by black cutworm larvae could be evident. Be on the alert for pinholes in the leaves as soon as the seedlings emerge. Although pinhole injury is not economic, it suggests that small cutworm larvae are present and could cause economic cutting injury as soon as the larvae are large enough. As a general rule, "rescue" insecticide applications may be warranted when 3 to 5 percent (or more) of 2- to 4-leaf seedling corn plants are being cut below ground. We will provide more details about scouting for cutworms, thresholds, and rescue treatments in next week's issue of the Bulletin.

Kevin Steffey (, Extension Entomology, (217)333-6652