k ^*' Cooperative Extension Service, University of 



~j— - Illinois College of Agriculture in Cooperation With i vr-^- : if '' • : 



A/K 7 the Illinois Natural History Survey and U.S.D.A. 



FOR IMMEDIATE RELEASE June 11, 19^5 



INSECT SURVEY BULLETIN NO. 8 



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

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

 versity of Illinois College of Agriculture, Illinois Natural History Survey and co- 

 operating 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. 



European corn borer pupation is complete except in extreme northern Illi- 

 nois, where 10 to 15 percent of the overwintering larvae will not emerge as moths 

 until late June or early July. Here moth emergence and egg laying will cover an ex- 

 tended period. However, in this area moth emergence now varies from 20 to 60 percent, 

 with an average of about 50 percent. In north-central Illinois, emergence ranges 

 from 50 to 75 percent; in central Illinois, from TO to 90 percent. 



A few egg masses can be found on the most advanced corn throughout the 

 northern one-half to two-thirds of Illinois. This week we did not find fields war- 

 ranting protective insecticide applications in the triangular area from St. Louis to 

 Springfield to Quincy. In this area many fields of corn are suitable for egg laying; 

 thus egg laying will be scattered, with no high concentrations expected in any field. 

 In the area north of the Springfield -Quincy line to a line from Rock Island to Kan- 

 kakee, borer eggs can be found, but not in any large numbers. North of this line, 

 egg laying has just started. 



In general, borer development this year closely parallels that of 1955 ar *d 

 i960, but corn development is slightly slower. The less mature the corn, the lower 

 the borer survival. Thus survival of borers should be low this year. In addition, 

 the rains and windstorms have probably killed many moths before they laid eggs. Even 

 though weather conditions of the next two weeks may be critical in determining the 

 corn borer potential, we now feel that the threat is not so great as it was a few 

 weeks ago. It should be apparent in the next three weeks whether it will be neces- 

 sary to use an insecticide to protect a field. 



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

 sel 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 hO to hj) 

 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 1/2 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. 



