year in the southeastern, southern, and west -southwestern sections of Illinois, sur- 

 vival is high and mortality is less than 10 percent. Preliminary surveys this week 

 in western Illinois indicate a 15-percent mortality. 



CLARIFICATION OF SOIL INSECTICIDE USES 



Our suggestions for using soil insecticides in Illinois cornfields have been: 



1. Where rootworms are not a problem: As a minimum use a diazinon seed treatment. 

 Otherwise apply 1.5 pounds of diazinon or 1 pound of Dasanit, Dyfonate, or 

 phorate (Thimet) at planting time in a 7- inch band on the soil surface ahead 

 of the press wheel. If you suspect that garden symphylans are present, use 

 Dyfonate at planting time. 



2. In fields where rootworm problems are anticipated: Apply Dasanit, Dyfonate, 

 or phorate (Thimet) as a 7-inch band on the soil surface ahead of the press 

 wheel; or, treat the seed with diazinon and apply BUXten or carbofuran as a 

 7-inch band ahead of the press wheel; or treat, the seed with diazinon and 

 make a basal application of BUXten, Dasanit, or phorate in June. 



3. We suggest that present supplies of aldrin and heptachlor be used up by ap- 

 plying them to fields of grass sods being plowed up for corn, to clover sods 

 to be planted to corn, or to fields to be planted to corn, where white grubs 

 are a problem. 



4. The reason for dropping aldrin and heptachlor from our general use soil -insecti- 

 cide recommendations is based on low yield returns for treatments, the continual 

 appearance of insect strains resistant to these chemicals, low wireworm popula- 

 tions, and the continual environmental contamination of insecticides with a long 

 residual life. 



In twelve fields where picker yields were compared in 1969, we had the following re- 

 sults : 



Organophosphates--118.7 bushels per acre 



Only diazinon seed treatment --111. 9 bushels per acre 



Nothing- -109. 9 bushels per acre 



Chlorinated hydrocarbons- -106. 3 bushels per acre 



Seven of these fields had sufficient corn rootworm populations to affect yields, 

 but five did not. Thus, we attribute these yield differences to the control of or 

 the failure to control rootworms, seed beetles, seed maggots, garden symphylans, 

 and perhaps other insects we failed to observe. Wireworms, cutworms, grape colaspis , 

 white grubs, corn root aphids , and sod webworms were not present in these fields. 



Wireworms, grape colaspis, corn root aphids, and sod webworms have not been a general 

 problem in Illinois for several years. Cutworms usually affect no more than 1 to 2 

 percent of the total corn acreage in Illinois. 



These facts influenced our thinking in making our 1970 suggestions to Illinois farmers 

 for soil-insect control practices in cornfields. For further information, see Circu- 

 lar 899, Insect Control for Field Crops. It is available from your county Extension 

 adviser. 



