INSECT 



SURVEY 



BULLETIN 





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College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



County 



Local Groups 



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FOR IMMEDIATE RELEASE 



U- flft LB$t8HF n Wt' i of ii»aticulture Cooperating 



AUG 19 1958 



August 9, 1968 



ILLINOIS I NSECT. DISEASE. AND WEED SURVEY BULLETIN NO. 22 



This series of weekly bulletins provides a general look at the insect, plant dis- 

 ease, and weed situation (fruit and commercial vegetables excepted) , along with 

 suggested, abbreviated control measures. Each individual should check his own 

 field to determine local conditions. 



CORN INSECTS 



Corn leaf aphid populations decreased rapidly this past week in fields where pol- 

 lination is complete. Ocassionally, such fields still have a high number of 

 aphids. Aphids can also be found in moderate to heavy numbers in late-maturing 

 fields that are still in the late-whorl to early silk stage. Adult, winged aphids 

 are especially common in these later-maturing fields, as they have migrated from 

 the earlier maturing fields. 



Treatment is justified on late-whorl-stage corn (a few tassels showing) if 50 per- 

 cent or more of the plants have aphids (a few heavy) and if the corn is under 

 stress (from low soil moisture, fertility, disease, etc.). Continue to watch the 

 infestation as long as growing conditions are good; if 15 percent or more of the 

 plants become heavily loaded with aphids, treat immediately. 



Corn rootworm adults are abundant in many fields in the northern half of the 

 state. The western corn rootworm was found for the first time in Kankakee County 

 last week, and this week in LaSalle County. If you live in a county where western 

 corn rootworms are not known to be present, take any specimens resembling this in- 

 sect to your county Extension adviser in agriculture for identification. 



In most fields, treatment with insecticides at this time will not be profitable. 

 But in late fields (where pollination may still be affected by silk feeding) or 

 in fields where adults are extremely numerous and are damaging ear tips, treat- 

 ment may still be justified. Treatment for adults in late-maturing fields is 

 recommended only if there are 5 or more beetles per ear, and if not over 50 per- 

 cent of the plants have silked. Sprays of carbaryl (Sevin) , diazinon, or mala- 

 thion at 1 pound of actual insecticide or 1/4 pound of methyl parathion per acre 

 are effective. Methyl parathion should be applied by experienced applicators only . 

 Allow 5 days between treatment and harvest for malatnion, 10 days for diazinon, 

 and 12 days for methyl parathion; carbaryl has no waiting period. Sprays of 

 malathion, methyl parathion, and diazinon will also control corn leaf aphids, 

 while carbaryl will not. 



Do not expect a single insecticide application for adult control to significantly 

 reduce the number of larvae that will be present in the field next year. Migra- 

 tion of the adult beetles from adjacent fields and prolonged emergence will provide 



