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More European Corn Borer Moth Captures Reported in Southern Illinois

May 11, 2001
Ron Hines, senior research specialist, Dixon Springs Agricultural Center, reported the capture of 13 European corn borer moths in a pheromone trap on May 8. Additional moths were caught in other pheromone traps. Ron indicated that these captures represent the greatest weekly totals in the last 4 years for his trapping location. Does this mean the first generation of European corn borers may cause more problems than anticipated? I think it is too early to answer this question. We'll continue to offer weekly updates on the status of the 2001 European corn borer flight. Please let us know of the first sightings of European corn borer moths in central Illinois. We would like to track the emergence of these moths throughout the state. This will enable us to offer more accurate predictions regarding the optimum time for scouting efforts to begin.

Entomologists have developed a system to predict the occurrence of different life stages and activity of European corn borers throughout a growing season, based on the initial capture of moths in the spring. By using May 1 as the first flight date in southern Illinois, we can predict when eggs are likely to hatch, and more importantly, when stalk boring will begin. When 212 heat units (base 50°F) have accumulated from the first spring flight, we should expect that egg hatch has occurred and first-instar larvae are beginning to create pinholes on corn leaves. Second instars and shot-hole leaf feeding can be found when 318 heat units (base 50°F) have accumulated. Third instars and stalk boring can be observed when 435 heat units (base 50°F) have accumulated. Treatment decisions must be made prior to the stalk-boring event because larvae that have tunneled into stalks cannot be killed with rescue treatments. By late this week and certainly by early next week, we should begin to observe some egg masses on corn plants in southern Illinois and possibly even some first-instar larvae.

Prospects for survival are dim for first-generation borers that find themselves on small corn plants. Southern Illinois producers who planted corn in late March or early April should monitor fields that in essence will serve as trap crops for egg-laying corn borer moths. Corn plants that are small (less than 18 inches, extended leaf height) are less susceptible to corn borer injury. Corn borers that feed on corn less than 18 inches in height typically fail to establish. The explanation for this response is the presence of a plant compound commonly referred to as DIMBOA (2-4 dihydroxy-7-methoxy-1, 4-benzoxazin-3-one), which prevents larvae from establishing. As plants mature, the concentration of DIMBOA decreases. Larval survival is much better on corn plants that are in mid- to late-whorl stage of development. Please let us know when you first begin to observe egg masses in your respective areas of the state.--Mike Gray

Scouting for first-generation European corn borer.

European corn borer egg mass.

First-instar European corn borer larvae hatching.

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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