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FOR IMMEDIATE RELEA SE June 16, I961 



INSECT SURVEY BULLETIN NO. 9 



This weekly bulletin on the general insect situation in Illinois (fruit 

 insects excepted) is prepared by entomologists of the Illinois Natural History Sur- 

 vey, University of Illinois College of Agriculture and cooperating agencies. It 

 is designed to forewarn people in Illinois of Impending changes in insect activity 

 and to suggest abbreviated control measures. These reports indicate only general 

 trends. Each individual should check his own fields to determine local conditions. 



Corn borer moths are now laying eggs throughout the more heavily infested 

 area, which is north of a line from St. Louis to Danville. In general, weather 

 conditions during the next three weeks may determine the severity of corn borer 

 this year. Wind and rain storms kill moths. Hot, dry weather that rolls the corn 

 leaves causes egg masses to fall to the ground, where the tiny borers will not sur- 

 vive. 



Moth emergence varies from 50 to 80 percent in south- central Illinois; 

 egg laying will continue for another two weeks in this area. Emergence in central 

 Illinois varies from 30 to 70 percent, and egg laying will continue for two to 

 three weeks. Emergence in northern Illinois varies from 10 to 50 percent, and egg 

 laying will continue for three to four weeks. 



Corn 30 inches and over, extended leaf height, in the area north of a 

 line from St. Louis to Danville and south of a line from Kankakee to Rock Island 

 had from 50 to 280 egg masses per hundred stalks this week. Hatch had just begun. 

 Start insecticide applications on the earliest fields in this area sometime the 

 week of June 26. North of this area egg laying is just beginning, and treatment 

 should probably start about the first of July. Cool nights will retard egg laying 

 and delay timing of treatments for best control. 



It is entirely possible that moths may continue to concentrate egg masses 

 in the most advanced fields of corn; borer survival in these fields will be high. 

 Therefore, observe these most advanced fields closely for the next three weeks. 



To determine the need for treatment, examine 50 to 100 plants for signs 

 of borer feeding on the whorl leaves. If 75 percent or more of the plants show 

 recent whorl feeding, check the tassel ratio. Measure from the base to the tip of 

 the plant with leaves extended. Split the plant lengthwise, and measure from the 

 base of the plant to the tip of the developing tassel. Divide the tassel height by 

 the plant height, and multiply by 100. Take an average of five representative 

 plants per field. This is the tassel ratio. The corn will warrant treatment if 

 the tassel ratio is 30 or above, but, if possible, treatments should not be applied 

 until the ratio is at least 35 and preferably k$. However, treatment after borers 

 have drilled into the stalk proper will not be effective. 



DDT is still the insecticide most commonly used for corn borer. Apply 

 1 1/2 pounds per acre as a spray or 3/^ to 1 pound per acre as granules. When 

 spraying, arrange two or three nozzles over the row to cover the upper one-third 

 of the plants, particularly the whorl zone. 



Other insecticides approved for use against corn borer include endrin and 

 toxaphene. Ensilage or stover of corn treated with DDT or toxaphene should not be 

 fed to dairy cattle. Endrin may be used in this case, provided label restrictions 

 are followed. 



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