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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 



August 16, 1968 



ILLINOIS INSECT. DISEASE, AND WEED SURVEY BULLETIN NO. 23 



This is the last issue of this series for 1968. We sincerely hope these 23 issuer 

 have been of help to you in the control of insect, plant disease, and weed control 

 problems in your community. Next year, we will have a new masthead. If you have 

 suggestions for an appropriate design, send us your ideas. We appreciate your 

 help and cooperation. 



CORN INSECTS 



European corn borer is still a problem to canning companies that process sweet 

 corn. As many as 100 egg masses per 100 stalks were still found this week in 

 mid-season to late plantings. Adhere to insecticide schedules for such fields. 

 Low populations of first-generation corn borers in early planted corn provide 

 many moths. Second-generation borers could be a problem if these moths concen- 

 trate their egg-laying on sweet corn; but if they also deposit eggs on late- 

 planted field corn, the pressure on sweet corn will be relieved to some degree. 

 Overall, we do expect a noticeable infestation of second-generation corn borers 

 in late corn in many areas of Illinois. 



Corn rootworm adults can now be found readily in many cornfields throughout the 

 state. The highest populations of beetles are still in the west, northwest, and 

 northeast sections. However, it is not uncommon to find fields of corn where 

 beetle populations average up to 10 per plant in central and eastern Illinois. 



In general, it is now too late to control beetles to prevent pollination injury. 

 Most fields have already pollinated. Treat late-maturing fields if there are 

 5 or more beetles per ear, and if not over 50 percent of the plants have silked. 

 Use 1 pound of carbaryl (Sevin) , diazinon, malathion, or 1/4 pound of methyl 

 parathion per acre. Methyl parathion should be applied by experienced applicators 

 only . Allow 5 days between treatment and harvest for malathion, 10 days for 

 diazinon, and 12 days for methyl parathion. Diazinon will 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 pro- 

 vide sufficient eggs to cause economic problems in 1969, if the field is planted 

 to corn again. However, it is possible that two or more applications ma)' kill 

 enough adults now to reduce the number of larvae next year. A random survey of 

 cornfields is now underway in 22 counties- -checking adult beetle populations, in 

 order to better estimate possible damage in 1969. 



