INSECT 



SURVEY 



BULLETIN 



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State 



County / Local Groups 



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College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



U. S. Department of Agriculture Cooperating 



FOR IMMEDIATE RELEASE 



INSECT SURVEY BULLETIN NO." 20 



,- 7 August 25, 1967 



This is the twentieth and final issue of a series of weekly bulletins that pro- 

 vides a general look at the insect situation (fruit insects excepted) along with 

 suggested abbreviated control measures. Each individ.ua! should check his own 

 fields to determine local conditions. 



Corn Insects 



Northern corn rootworm adults can still be found in a great many cornfields, and 

 they are also present in small numbers in nearby clover fields. These green or 

 yellowish- green beetles are still emerging from the soil in the northern part of 

 the state. Egg-laying has probably begun. Control of these adults is not profit- 

 able at this time of the season, unless these adults are doing considerable damage 

 to kernels on the ear tips. 



Western corn rootworm adults in northwestern Illinois are feeding on some of the 

 ear tips. These striped beetles are also feeding on the surface of corn leaves 

 and on some brace roots. Control of western corn rootworm adults can be justified, 

 if the number of adults is in the range of 15 to 20 beetles per plant. The con- 

 trol of adults should help to reduce egg- laying, resulting in somewhat fewer larvae 

 next year. However, control of adults will not prevent problems with larvae in 

 1968, if the field will be in corn again . Sprays of carbaryl, diazinon, or mala- 

 thion at 1 pound per acre of actual insecticide are effective. Commercial appli- 

 cators may prefer to use 1/4 pound of parathion per acre. Allow 5 days between 

 treatment and harvest for malathion, 10 days for diazinon, and 12 days for para- 

 thion; carbaryl has no waiting period. 



An ideal time to assess the corn rootworm situation in a cornfield is at this time 

 of year. If no rootworm adults are present on or around the corn plants, then 

 control has been achieved by either chemical or cultural methods- -usually rotation. 

 If rootworm adults are present with a range of 5 or more beetles per plant, then 

 there were larvae damaging the corn roots. If the beetles are very numerous, and 

 the plants are lodged, and chemical control with either aldrin or heptachlor was 

 used several years in succession, then the rootworms have become resistant. 



European corn borer moths are still laying eggs in northern Illinois. Unseasonably 

 cool nights have reduced egg- laying, but some late -maturing fields in the north- 

 western section of the state are attractive to moths as egg- laying sites. 



Fall armyworm damage is evident in some late-maturing cornfields. These brown to 

 dull -green, smooth- skinned worms feed in the whorl, giving plants a ragged appear- 

 ance as the leaves emerge. Unless 20 to 25 percent of the plants still have worms 



