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INSECT 



SURVEY 



BULLETIN 



8 





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tate / County / Local Groups 



FOR IMMEDIATE RELEASE 



College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



U. S. Department of Agriculture Cooperating 



JUL 2 9l96|o 



July 26, 1968 



ILLINOIS INSECT, DISEASE, AND WEED SURVEY BULLETIN NO. 20 



This series of weekly bulletins provides a general look at the insect, plant dis- 

 ease, and weed situation (fruit and commercial vegetables excepted) , along with 

 suggested, abbreviated control measures. Each individual should check his own 

 fields to determine local conditions. 



THE LIBRARY I 



INSECTS 



AUG -1 



Corn 



[;.■_:_'_.-._:,: ;... li LihiiiS 

 Corn leaf aphids are still present in most cornfields in light to moderate num- 

 bers. A few fields have heavy populations. Fields still in the late-whorl or 

 early-tassel stage are the most critical, especially if soil moisture is low. 

 Fields of corn with fully exposed tassels and in which pollen shed is about com- 

 plete will probably escape damage, unless infestations are extremely severe. In- 

 festations in these fields are already beginning to decline. 



Examine fields of corn in the late-whorl to early-tassel stage, especially if the 

 soil moisture has been less than adequate. 



To examine a field for aphids, (1] pull 25 whorls in four places in a field, 

 (2) unroll the leaves, and (3) determine the percent of infested plants and degree 

 of damage. If the next two weeks are hot and dry, the population of aphids is 

 most likely to increase greatly- -decreasing with cool, rainy weather. We have 

 observed very few predators. The black beetles with the four yellow spots, com- 

 monly seen in the whorl, are picnic beetles. They are not predators and do not 

 damage plants . 



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

 cent 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. Allow 5 days between treatment and harvest for malathion 

 and 10 days for diazinon. If corn is still in the late-whorl stage, seed producers 

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

 granules. To avoid potential hazards to detasselers, use phorate only on male- 

 sterile corn. 



