Southern Corn Leaf Beetle Has Caused Significant Damage in Western Illinois

May 12, 2000
There is little doubt now that the southern corn leaf beetle has established itself as an insect to cope with in western and southern Illinois. I also have heard reports of this insect causing problems in Missouri and in the southern tier of counties of Iowa. Although several people have dealt with it in the past, most of them report that they have never witnessed the numbers of fields infested that they have observed this year. Apparently the mild winter and early planting enhance this insect's pest status. In addition, several people have determined that southern corn leaf beetles are more common in no-till or reduced-tillage systems.

Several people have called or emailed reports of injury caused by this insect during the past week, and some of them have sent some pretty good photographs. I applaud the latter effort because the beetles are very small and difficult to photograph. Jeff Staley with Wabash Valley FS found southern corn leaf beetles in Gallatin County and sent a photo of the characteristic notching injury. Tracy Cameron with Crestland Co-Op in southwestern Iowa reported that these pests can be found in the southern half of the southern tier of counties in the state. Tom McMurren, district manager for the western Illinois territory for AFS Services, reported lots of damage and high numbers this year.

Southern corn leaf beetle adult. (Photo courtesy of Tom McMurren, AFS Services.)

I reported in last week's issue (no. 6, May 5, 2000) of the Bulletin that southern corn leaf beetle had been added to the Capture 2EC label for corn. More recently, Zeneca Ag Products has issues a FIFRA Section 2(ee) recommendation for Warrior T for suppression (their underline) of southern corn leaf beetle in field, sweet, and seed corn in Illinois only. The recommendation must be in the possession of the user at the time of pesticide application. The application rate is 3.84 ounces per acre. In bold print, the label states: May be applied through chemigation equipment. Apply in a minimum of 2 gallons per acre by air or 10 gallons per acre by ground. When pest populations are high, 5­10 gallons per acre by air or 20 gallons per acre by ground and higher use rates are recommended (my italics). I italicized the latter portion of the previous sentence because only one rate is listed on the label. Using higher-than-labeled rates of application is not legal.

David Thomas with Zeneca also faxed me a copy of some efficacy data generated in 1998 by entomologists and extension personnel at Kansas State University. The field was located near Troy, Kansas, not too far from St. Joseph, Missouri. The products tested and their rates of application were as follows: Ambush 2E at 0.1 lb a.i. per acre; Baythroid 2E at 0.025 and 0.031 lb a.i. per acre; Lorsban 4E at 1 lb a.i. per acre; Pounce 3.2EC at 0.1 lb a.i. per acre; and Warrior T at 0.02 and 0.03 lb a.i. per acre. The number of living adults in the untreated plot was significantly higher than the numbers of living adults in all plots treated with insecticides. The numbers of living adults in plots treated with Ambush and in plots treated with Warrior at 0.02 lb a.i. per acre were significantly higher than the numbers of living adults in all other insecticide-treated plots. Baythroid applied at both rates and Lorsban, Pounce, and Warrior applied at 0.03 lb a.i. per acre (3.84 oz per acre) provided equivalent control. However, Baythroid is not registered for use on corn. In their notes accompanying the data, the following is attributed to Randy Higgins, an Extension entomologist at Kansas State University: "Higgins believes that it is possible that the insect may have been causing damage for years with the damage mistaken for black cutworms during years when it had been a problem. Damage strongly resembles severe cutworm injury." Randy may be right, which further emphasizes the need for accurate diagnosis before insect control is initiated.

It's clear that we need to learn more about the southern corn leaf beetle. Its widespread occurrence this year has captured considerable attention. If you have additional observations about this insect, please continue to send them to us. Every little piece of the puzzle helps.--Kevin Steffey

Author: Kevin Steffey