INSECT 



SURVEY 



BULLETIN 



ABT£*fe 





.0 



FOR IMMEDIATE RELEASE 



College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



U. S.lft<MBRAR¥iflFifH&f Agriculture Cooperating 



AUG 1 9 1368 



imwrniv flf immiQ 



August 2, 1968 



ILLINOIS INSECT, DISEASE. AND WEED SURVEY BULLETIN NO. 21 



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

 ease, and weed situation (fruit and commercial vegetables excepted) 3 along with 

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

 fields to determine local conditions. • PRmtY Or THE 



INSECTS 



AUa -J 



13B9 



torn 



WMM HE ILLINOIS 



Corn leaf aphids increase rapidly in number in corn from pretassel to late silking. 

 How soon will these aphids decrease? They decrease after pollination has occurred. 

 After silks are dry, they disappear rapidly from the field. 



Several other questions are being asked. The white objects in the aphid colony 

 are the shed skins of aphids- -not dead aphids or aphid eggs. There are no aphid 

 eggs. In fact, there are no male aphids during the summer months. All aphids are 

 females that give birth to living young. The black on the corn plants Is sooty 

 mold growing on the honey-dew secretion of the aphids. This is also present on 

 plants without aphids. This sooty mold will wash off with rain and the plants will 

 look greatly improved. 



Stress on the corn plant is all important. A drought during an aphid outbreak can 

 be extremely serious. If plant roots are pruned for any reason (as by rootworms) , 

 the aphid damage will be greater than to plants with normal root systems. 



In general, the aphid situation is not serious in most areas of adequate moisture, 

 because the light to moderate infestations are not damaging. Some people become 

 excited and refer to light or moderate infestations as "heavily loaded plants." 

 A heavily loaded plant is one with the tassel plus several of the upper leaves 

 literally coated with aphids. 



This week, aphid populations decreased rapidly in fields already pollinated, and 

 they started to decrease in fields that were pollinating. Fields in the late- 

 whorl or early tassel stage should be observed carefully this week. 



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

 percent or more of the plants have 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. 



