f~~ h Cooperative Extension Service, University of 



Illinois College of Agriculture in Cooperation with 

 the Illinois Natural History Survey and U.S.D.A. 



FOR IMMEDIATE RELEASE May 21, I965 



INSECT SURVEY BULLETIN NO. 5 



This is the fifth in a series of weekly bulletins on the general insect 

 situation in Illinois (fruit insects excepted), prepared by entomologists of the 

 University of Illinois College of Agriculture, Illinois Natural History Survey and 

 cooperating agencies. It is designed to forewarn people in Illinois of impending 

 changes in insect activity and to suggest abbreviated control measures. These re- 

 ports indicate only general trends. Each individual should check his own fields 

 to determine local conditions. 



Corn borer pupation is complete in the southern six to 10 Illinois coun- 

 ties; 50 percent of the moths have already emerged, and egg laying has started. 

 Advanced fields had a maximum of one egg mass per plant this week. Egg laying will 

 continue for two weeks, taper off and be complete in three weeks. After most of 

 the eggs have hatched, decide whether an insecticide application will be profitable. 

 Only the earliest fields will warrant use of insecticide. 



To decide whether an insecticide can be profitably applied, measure the 

 tassel ratio of the field and count the percent of plants with recent whorl leaf 

 feeding. To determine the tassel ratio, measure the height of the plant with 

 leaves extended; split the stalk open and measure from the tip of the developing 

 tassel to the base of the plant. Divide the tassel height by the plant height, and 

 multiply by 100. This figure is the tassel ratio. If the tassel ratio is at least 

 35 (preferably kO to 45) and at least 75 percent of the plants show recent whorl 

 feeding, then treatment is justified. Use 1 pound of actual diazinon in granular 

 form per acre or 1 l/2 to 2 pounds of carbaryl (Sevin) as granules. For spraying, 

 use the same amount of actual insecticide per acre, and direct the spray to the 

 upper third of the plant. Aerial applications should be granules, not sprays or 

 dusts. Follow the label precautions in harvesting and feeding treated corn. DDT 

 can be used as granules or sprays, but not on or adjacent to dairy farms. 



In central and northern Illinois, 10 to 50 percent of the overwintering 

 borers have pupated, but no emergence of consequence is expected for at least 10 

 days or perhaps two weeks. In general, except for an occasional early field, borer 

 development is ahead of corn development. Borer moths may concentrate in extremely 

 advanced corn in the area north and west of a line from St. Louis to Springfield to 

 Hoopeston and south of a line from Kankakee to Rockford. Starting in mid- June, be 

 prepared to examine these fields regularly. 



Armyworm populations do not approach those of last year, but the worms 

 are still very small in most fields and some eggs are still hatching. Only an oc- 

 casional field of extremely luxuriant wheat in the southern half of the state has 

 enough worms to warrant application of an insecticide. Fields of wheat averaging 

 one or two armyworms per linear foot of drill row are not uncommon throughout this 

 area, but this population neither requires the use of an insecticide nor can it be 

 justified unless the worms concentrate on cutting heads. 



Tnt LIBRARY 6F W 

 MAY 2-1 ;:5 

 BM!V»SITir PF lUHUflfS 



