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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 4, 1967 



INSECT SURVEY BULLETIN NO. 17 



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 



Adult corn rootworms are feeding on silks in many cornfields throughout the state. 

 Many fields in northern Illinois have an average of 5 or more beetles per plant. 

 But, there are more to come. There are many fields in this area with a third of 

 the rootworms yet to emerge as adults during the next two weeks. One field aver- 

 aged 6 to 8 beetles per plant with an infestation of 50 to 55 rootworms per plant 

 still in the soil. The western corn rootworm was found for the first time this 

 week in Winnebago and Jo Daviess counties. 



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. Treat- 

 ments after 90-percent silk are of little benefit. Throughout the state most 

 cornfields are beyond 90-percent silk and pollination has taken place. These 

 fields will not be affected from silk feeding by the beetles. 



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 

 malathion, 10 days for diazinon; carbaryl has no waiting period. Control of 

 adult beetles will reduce egg laying and will result in fewer larvae in the field 

 next year. However, adult control is no guarantee that problems with larvae will 

 not occur in 1968. 



During the next week or two, you should check your cornfields to determine if a 

 problem with northern corn rootworms is developing. If you have grown corn for 

 several years in succession in the field, if you have used aldrin or heptachlor 

 almost every year, if the corn is lodged (maybe only spots) , and if there are 

 lots of pale -green beetles (5 to 10 or more per plant on the average) on the 

 fresh silks, you most likely have resistant northern corn rootworms. 



In the limited area of infestation (western section of Illinois) of the resistant 

 western corn rootworm, make a count of the average number of beetles per plant 

 when the corn is in fresh silk. An average of 5 to 10 or more adults per plant 

 is probably enough to cause economic losses in 1968 if .the field .will be in corn 

 again. Tnt L . 



AUG 13 





