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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 



August 11, 1967 



INSECT SURVEY BULLETIN NO. 18 



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 



Corn rootworm beetles are gradually increasing in abundance in cornfields, where 

 they are concentrating in the corn silks. In most fields, pollination has been 

 completed and silk feeding is not important. We observed a few heavily infested 

 fields (20 or more beetles per plant) where the adults were feeding on and dam- 

 aging ear tips. Treatment of these fields is justified. Treatment with insecti- 

 cides in the majority of fields at this time will not be profitable, except in 

 late fields, where pollination may still be affected by silk feeding. 



Treating adults now with the hope of reducing numbers of larvae in the same field 

 next year offers little promise. We do not suggest controlling adult rootworms 

 after the field has completed pollination. Migration of adult beetles from adja- 

 cent fields and prolonged emergence make late summer insecticide applications less 

 effective. 



In late-planted fields of corn, where silking averages 25 to 75 percent and there 

 are 5 or more rootworm beetles per plant, treatment will be profitable. ( Note : 

 Do not confuse the tan- to green-colored northern corn rootworm adults with the 

 small, wingless, soft-bodied green tarnished plant bug nymphs .) 



Sprays of carbaryl (Sevin) , diazinon, or malathion at 1 pound of actual insecti- 

 cide per acre are effective. Allow 5 days between treatment and harvest for mala- 

 thion, 10 days for diazinon; carbaryl has no waiting period. 



Western corn rootworm adults were found this week for the first time in Stephenson, 

 Fulton, and McDonough counties. 



Second- generation European corn borer moth emergence and egg laying are progress- 

 ing in northwestern and western Illinois. Heavy moth flights were observed in 

 both sections this week. Moths will continue to emerge and lay eggs for at least 

 three weeks. Half -grown second -generation larvae and egg masses were observed 

 in some fields in central sections. The heavy rains in some localities may have 

 destroyed egg masses and killed many moths. 



Although moths will deposit eggs on all corn, they concentrate their egg flaying 



in fields in the late whorl to early silk stage. Second-brood jft<jlihs generally 



lay their eggs in clusters of 15 to 20 near the mid-rib on the undersides of leaves 



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