University of Illinois

No. 8/May 16, 1997

Status Report for Black Cutworms

Several people scouting in fields with emerged corn seedlings have reported leaf-feeding injury apparently from young black cutworm larvae. For several weeks, we have been predicting when evidence of cutting injury caused by fourth-instar cutworms could be observed in different areas of the state. These projected dates have continued to move ahead due to the cool temperatures. Cutworm larvae do not develop rapidly when temperatures are cool. Consequently, recent observations of leaf feeding, noneconomic injury caused by small black cutworm larvae, is right in line with our most recent projections. Table 1 shows an array of dates of intense moth captures, the counties where the captures occurred, and the projected dates when 300 heat units above 50 degrees F will accumulate after an intense moth capture (nine or more moths captured over a 1- to 2-day period). By the time you receive this issue of the Bulletin, cutting injury could be evident in several southern counties. During the week of May 19, cutting injury could be evident in southern and central Illinois counties.

Scouting for black cutworms should be under way. Scouting guidelines and the head capsule gauge for determining the stage of development of black cutworm larvae were in last week's issue (no. 7, May 9) of this Bulletin. Effective insecticides suggested as "rescue" treatments for black cutworms are *Ambush 2E at 6.4 to 12.8 oz per acre; *Asana XL at 5.8 to 9.6 oz per acre; Lorsban 4E at 1 to 2 pt per acre; *Pounce 3.2EC at 4 to 8 oz per acre; and *Warrior 1EC at 1.92 to 3.2 oz per acre. Please follow all label directions and precautions, and avoid pesticide drift.
Kevin Steffey, Extension Entomology, (217)333-6652

Table 1. Potential dates when 300 heat units above
50 degrees F have accumulated from an intense moth
capture, indicating when black cutworm larvae are
large enough (fourth instar) to cut corn seedlings.

Date of moth captureCounty of moth captureProjected date when 300 heat units (base 50F) have accumulated
March 24RandolphMay 13
March 26AlexanderMay 14
April 1MonroeMay 16
April 11ClarkMay 21 or 24
April 12Macon May 22 or 24
April 13FranklinMay 20
April 16HancockMay 21 or 24
April 16VermilionMay 24
April 19ClarkMay 22
April 26PikeMay 22
April 28FordMay 27 or 28
April 29AdamsMay 23
May 3Clark May 29 or 26
May 6PikeMay 27
May 6WayneMay 27
May 7LaSalleMay 31 or June 2

Note: Two dates may be listed for the same county if
the heat-unit accumulations were generated from
different Illinois Climate Network sites.