Al / 



COLLEGE OF 

 AGRICULTURE 

 UNIVERSITY OF 

 ILLINOIS AT 

 URBANA-CHAMPAIGN 

 AND NATURAL 

 HISTORY SURVEY 

 URBANA. ILLINOIS 



NSECT WEED & PLANT DISEASE SURVEY BULLETIN 



ATE/COUNTY/LOCAL GROUPS/U.S. DEPARTMENT OF AGRICULTURE COOPERATING 



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FOR IMMEDIATE RELEASE 





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Art ovSNo. 12, June 19, 1970 



2%£s series of weekly bulletins -provides a gene$*fj$,\}&%ffiCat the insect, weed, and plant 

 disease situation (fruit and commercial vegetables excepted) , along with suggested, 

 abbreviated control measures . Each individual should check his own fields to determine 

 local conditions. 



INSECTS 



CORN 



European corn-borer infestations should be watched carefully for the next three weeks . 

 Wait until you are sure treatment is warranted, but do not allow fields to suffer 

 noticeable economic loss. 



A few cornfields (1 to 5 percent of the total) everywhere are much more advanced than 

 others. In the south, west, and northwest parts of the state, such fields either show 

 or will soon show noticeable feeding on the whorl leaves. In the east, central, and 

 northeast sections (where overwintering borer populations were low) , fewer fields will 

 be affected. 



In southern Illinois, small borers will soon leave the whorl as the tassels emerge and 

 enter the stalk. Once there, they are difficult to reach with insecticides. This 

 will occur within the next week in those very early fields. Thus, the time to apply 

 insecticides has almost gone by in the area south of a line across the state opposite 

 St. Louis. Eggs are still being deposited on corn north of this line almost up to 

 Rock Island- -with a few fields, particularly on the west side of the state, already 

 meeting the standards for profitable insecticide application. The optimum timing will 

 be during the next two weeks. 



The emergence of moths is almost complete in northern Illinois, and egg-laying is just 

 starting. A few fields will probably be damaged. The optimum time period for applica- 

 tions to field corn will probably start 10 days to two weeks from now. 



In general, the storms of this past week killed some moths. This will help reduce the 

 overall, first -generation borer population. Nevertheless, watch those early fields 

 closely. 



To determine the need for treatment, first check the tassel ratio. Dig up a plant and 

 measure from the bottom of the plant to the tip of the longest leaf. Split the plant 

 and find the developing tassel. Measure from the bottom of the plant to the tip of the 

 tassel. Divide the tassel height by the plant height and multiply by 100. If the tas- 

 sel ratio is 30 or over and if 75 percent or more of the plants have corn-borer feeding 

 on the whorl leaves, the field should be treated- -but not until the tassel ratio is at 

 least 35, preferably 40 to 50. The percentage of infested plants required to justify 

 treatment can be reduced with higher tassel ratios . 



