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Cooperative Extension Service, University of 

 ^T/kc I Illinois College of Agriculture in Cooperation With 



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



FOR IMMEDIATE RELEASE June 25, 196$ 



INSECT SURVEY BULLETIN NO. 10 



This is the tenth 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 coop- 

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

 in insect activity and to suggest abbreviated control measures. These reports indi- 

 cate only general trends. Each individual should check his own fields to determine 

 local conditions. 



European corn borer is less important now than it was last week. The storms 

 of the past week killed many moths, especially through the central and north-central 

 sections. Only these moths in highly protected areas were able to survive. Moth 

 emergence is complete except north of Interstate 80, where a few pupae remain. 



In the area south of Route 136, egg laying is complete, and even the more 

 advanced fields show only a light incidence of corn borer. It is unlikely that chemi- 

 cal control will be needed in this area. 



In the area between Route 136 and Interstate 80, the percentage of fresh 

 eggs is small, but a few eggs will still be laid next week. However, because a 

 higher percentage of the corn is acceptable to moths for egg laying, the eggs will 

 be scattered over many fields rather than concentrated in a few. Occasional fields 

 in this area may justify treatment. 



In the area north of Interstate 80, egg laying will continue for another 

 10 days to two weeks. In general, corn growth here is below normal, so borer sur- 

 vival will be low. Occasional early-planted fields show economic infestations. Watch 

 these early-planted, more mature fields (over 50 inches), as moths will concentrate 

 their egg laying here. 



First-generation corn borers are beginning to pupate in extreme southern 

 Illinois. Three generations could occur in this section this year. 



To decide whether an insecticide can be profitably applied, count the per- 

 cent of plants with recent whorl leaf feeding, and measure the tassel ratio of the 

 field. 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 (pref- 

 erably kO to U5) 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 pre- 

 cautions in harvesting and feeding treated corn. DDT can be used as granules or 

 sprays, but not on or adjacent to dairy farms. 



Chinch bug nymphs are abundant in thin stands of grain and in thin spots of 

 thicker stands in east-central Illinois. They can also be found on corn where a grain 

 or grass crop was plowed down before planting. Hot, dry weather favors chinch bug 

 development ; wet weather promotes the spread of a fungus disease that kills many of 

 them. , m 



