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INSECT 



SURVEY the L;e^y%:^ 

 BULLETIN j UL 25 i%roo^ 



College of Agriculture 



University of Illinois U^i/fBV'rv nt ij m mpi » 



and Natural History Survey: Ur-|4WvA -II lino 



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S. Department of Agriculture Cooperating 



FOR IMMEDIATE RELEASE 



July 14, 1967 



INSECT SURVEY BULLETIN NO. 14 



This series of weekly bulletins provides a general look at the insect situation 

 (fruit insects excepted), along with suggested, abbreviated control measures. 

 Each individual should check his own fields to determine local conditions. 



Corn Insects 



Corn leaf aphid populations continued to increase this week. A few fields in the 

 southern half of the state warrant treatment. In the northern half of the state, 

 a few aphids can be found in most fields. In the western and northern sections, 

 individual aphids and sometimes a colony were present in from 5 to 50 percent of 

 the plants in fields with tassels just beginning to show. 



Swollen brown-colored aphids, parasitized by a tiny wasp, were observed this week. 

 Lady beetles, syrphid flies, aphis lions, and other predators also eat aphids. 

 If many aphids appear parasitized or if predatory insects are abundant, it may 

 not be wise to apply an insecticide. 



Leaf -aphid infestations usually begin when the tassel is deep in the whorl, reach- 

 ing their peak between tassel emergence and the end of pollen shed. Infestations 

 decline rapidly after pollen shed, except for occasional fields where populations 

 remain high until harvest. 



Treatment is justified on late-whorl -stage corn (a few tassels showing) , if 50 

 percent or more of the plants have some aphids (a few heavy) and if the corn is 

 under stress (from low soil moisture, fertility, disease, etc.). Continue to 

 watch the infestation as long as growing conditions are good; if 15 percent or 

 more of the plants become heavily loaded with aphids, treat immediately. Seed 

 fields should be treated if 50 percent or more of the plants have some aphids 

 (only a few heavy), even if the corn is not under stress. In general, applica- 

 tions after all the silks have dried are disappointing. 



Spray treatments by ground or air with 1 pound of malathion or diazinon per acre 

 will control the aphids. When using malathion, allow 5 days between treatment 

 and harvest for grain, ensilage, or stover. There is no waiting period between 

 treatment and harvest for grain when using diazinon, but allow 10 days to elapse 

 before making ensilage or stover. If corn is still in the late-whorl stage, seed 

 producers may prefer to use 1 pound of either diazinon or phorate (Thimet) as 

 granules per acre. To avoid potential hazards to detasselers, use phorate only on 

 male-sterile corn. 



