University of Illinois

No. 8/May 16, 1997

Flea Beetles Attacking Corn Seedlings in Several Locations

During the latter part of the week of May 5 and the early part of the week of May 12, we received several reports of economic or near-economic levels of infestation of flea beetles in corn fields. Infestations of flea beetles have been reported from Clark, Effingham, Fayette, Lawrence, and Montgomery counties, and a few additional counties in western Illinois. Don Rhodes with Burrus Power Hybrids observed as many as 12 flea beetles per plant during his visit to some fields in Missouri. Bill Brink, Extension educator in crop systems at the Springfield Extension Center, reported 4 to 6 per plant in a field in Montgomery County. And Randy McElroy, regional agronomist with DeKalb Genetics Corporation, indicated that some fields of seed corn in Effingham County have already been sprayed for control of flea beetles. In fields of 1- to 2-leaf corn in Clark, Effingham, and Lawrence counties, some corn seedlings were wilted; and others were nearly dead due to extensive feeding by flea beetles.

In issue no. 2 (April 4) of this Bulletin, we indicated that based upon the sum of the average temperatures of December, January, and February, flea beetle survival north of Interstate 70 was not expected to be good. Although these average winter temperatures offer a clue regarding flea beetle survival, snow cover is not considered. Consequently, even when winter temperatures are cold, snow cover may insulate the overwintering beetles and protect them. However, we have received few reports of flea beetle problems north of Interstate 70, so the prediction might have been relatively accurate. Nevertheless, we encourage scouting for flea beetles right now in any area of Illinois where corn seedlings are growing slowly.

Corn flea beetles are only 1/16 inch long, are shiny black, and have enlarged hind legs that enable them to jump when disturbed. They injure corn by feeding on the epidermis of leaves, causing small feeding streaks or windowpane feeding patches. Although this injury usually does not cause economic yield loss, if the numbers of beetles are great and the corn is not growing vigorously, the seedlings may wilt and die. Corn flea beetles also transmit the bacterium Erwinia stewartii, the causal agent of Stewart's bacterial wilt. The bacterium overwinters both in flea beetles and in soil and plant residue. Seedling corn infected by the bacteria may become stunted, wilt, and display linear lesions with wavy edges on the leaves. Sweet corn varieties and sensitive inbred lines planted in seed-production fields are more susceptible than commercial corn hybrids to injury caused by corn flea beetles and to Stewart's bacterial wilt.

As you scout fields of seedling corn, look for flea beetles and the symptoms of the injury they cause. The suggested economic threshold in hybrid corn is five or more beetles per plant. In seed-corn production fields, treatment may be justified if 10 percent of the plants inspected have severe flea beetle-feeding injury and there are two or more beetles per plant. However, these thresholds are based upon relatively good growing conditions. Reduce the thresholds if the seedlings are growing poorly and the injury caused by flea beetles is severe. Use your best judgement.

If an insecticide application for control of flea beetles is warranted, several products are effective. Refer to Table 2 for labeled rates of insecticides suggested for control of flea beetles in seedling corn. Please follow all label directions and precautions, and avoid pesticide drift.
Kevin Steffey, Extension Entomology, (217)333-6652

Table 2. Insecticides suggested for control of flea
beetles in seedling corn.

InsecticideAmount of product per acre
*Ambush 2E6.4 to 12.9 oz
*Asana XL5.8 to 9.6 oz
*Furadan 4F2.5 fl oz per 1,000 row ft
Lorsban 4E2 to 3 pt
*Penncap-M2 to 3 pt
*Pounce 3.2EC4 to 8 oz
Sevin XLR Plus2 pt
*Warrior 1EC2.56 to 3.84 oz

* Use restricted to certified applicators.