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INSECT 



SURVEY 



BULLETIN 



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College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



State / County / Local Groups / U. S. Department of Agriculture Cooperating 



FOR IMMEDIATE RELEASE 



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gun y- ;i 1967 



INSECT SURVEY BULLETIN NO. 11 



June 23, 1967 



This series of weekly bulletins provides a general look at the insect situation 

 (fruit insects excepted), along with suggested, abbreviated control measures. 

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



Corn Insects 



European corn borer egg laying is declining in the central sections ; egg laying 

 is presently at its peak in the northern sections (north of Highway 6) . In the 

 west -southwest and west -central sections, egg counts ranged from 30 to 100 per 

 100 plants ; 20 to 90 percent of the plants were showing recent whorl feeding in 

 the most advanced fields . The average height of the corn in these fields was 

 40 to 57 inches, with tassel ratios of from 8 to 26. Egg counts in the northern 

 sections varied from 20 to 100 per 100 plants (mostly unhatched) ; 5 to 20 percent 

 of the plants were showing recent whorl feeding in the most advanced fields. The 

 average height of the corn in these fields was 35 to 44 inches, with tassel ratios 

 of from 5 to 12. 



Examine the rapidly -growing, most-advanced fields in west -southwest (especially 

 in bottom land areas) and west-central sections for corn borer infestations. 

 Treatments, if needed, should be underway in the west -southwest section and should 

 be started this week in the west-central section. Begin checking the advanced 

 fields in the northern sections this week for corn borer infestations. Treatments, 

 if needed, should begin about July 1. 



In many areas, there are no exceptionally advanced fields, and the moths are scat- 

 tering their eggs over many fields instead of concentrating them in a few. The 

 heavy rains this week may have killed many moths. In addition, a protozoan dis- 

 ease is quite common in recently collected pupae and adults (60 -percent infection) . 

 The rains plus the disease could shorten the egg- laying period and help reduce 

 the number of corn borers . 



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

 ratio of the field and determine the percent of plants with recent feeding in 

 the whorl leaves. To determine the tassel ratio, measure the height of the plants 

 with leaves extended; split the stalk open and measure from the tip of the develop- 

 ing tassel to the base of the plant; divide the tassel height by the plant height; 

 and multiply by 100. That figure is the tassel ratio. If the tassel ratio is at 

 least 55 (preferably 40 to 45) and at least 75 percent of the plants show whorl 

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

 per acre or 1 1/2 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 



