Cooperative Extension Service, University of liKiVtRSii V Of ILLINOIS, 



Xri Illinois College of Agriculture, in Cooperation with 



-^ ' the Illinois Natural History Survey and U.S.D.A. 



FOR IMMEDIATE RELEASE August 6, I965 



INSECT SURVEY BULLETIN NO. 16 



This is the sixteenth in a series of weekly bulletins on the general insect 

 situation in Illinois (fruit insects excepted), prepared by entomologists of the Uni- 

 versity of Illinois College of Agriculture, Illinois Natural History Survey and co- 

 operating agencies. It is designed to forewarn people in Illinois of impending 

 changes in insect activity and to suggest abbreviated control measures. These reports 

 indicate only general trends. Each individual should check his own fields to deter- 

 mine local conditions. 



Western corn rootworms were found in numbers in one field of corn in west- 

 ern Illinois this week. There was no commercial damage to the corn, but it was quite 

 easy to collect dozens of beetles. Whether or not there are other similarly infested 

 fields is a matter for conjecture; however, individual specimens were also found in 

 three other fields. 



This rootworm is new to Illinois and is the one that has caused the severe 

 problems in western Iowa, Nebraska, Kansas, and South Dakota,, as well as in localized 

 areas in Missouri and Minnesota. The beetles in those states are highly resistant 

 to the soil insecticides aldrin and heptachlor, and the beetles collected in Illi- 

 nois are probably also resistant. 



We can see no reason for farmers to become excited at this time. Larval 

 damage by both northern and western corn rootworms is over and will, not occur again 

 until next year. We will have an opportunity to examj ne research results of control 

 methods obtained by other states before next year, and no control measures can be 

 applied now. 



Northern corn rootworm adults are abundant in. some fields ,_ but in a survey 

 of 30 fields we found only two that had large numbers of beetles. In neither case 

 was resistance to soil insecticides involved. We do expect-, however, to run into some 

 problems of resistance. 



Corn leaf aphids continue to be a problem* - Unless a high percentage of the 

 plants are severely infested, we do not believe it will be profitable to apply in- 

 secticides to fields that are already pollinated or are pollinating. Plants in pre- 

 tassel or younger can be damaged more readily. 



Phorate granular applications of two weeks ago have continued to be effec- 

 tive in preventing aphid build-up, but the diazinon granular applications have begun 

 to break down and aphid populations in these plots are increasing. Sprays of diazi- 

 non, malathion^ mevinphos (Phosdrin) and parathion will also- control these aphids. 



Do not use phorate if it was used as a soil insecticide, .and even then do 

 not apply later than whorl stage. Mevinphos and parathion sprays should be applied 

 only by operators prepared to use protective clothing. Phorate granules can be used 

 by the individual, but extreme care must be taken in handling. Diazinon granules can 

 be used to within 2 days of harvest, malathion to within 5 days, parathion to within 

 12 days and mevinphos to within 1 day. 



