T/V7 



FOR IMMEDIATE RELEASE 



INSECT 



SURVEY 



BULLETIN 



*«"»% 



,# 



College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



U. S. Depar 



urtrnent of Agriculture Cooperating 



JUL 2 



357 July 7, 1967 



INSECT SURVEY BULLETIN NO 



^jttounif juijifiK 



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 aphids can be found in the whorl of corn in the southern half of the 

 state. Individual aphids- -not colonies --can be found in some cornfields in the 

 northern half of the state. Aphids are also present on grasses and will soon 

 move to the corn. Many winged forms were observed this week indicating that 

 aphids are migrating at this time. Occasional fields of corn in the late whorl 

 stage (occasional tassels showing) in the southern half of the state have heavy 

 aphid numbers. Leaf aphid infestations usually begin when the tassel is deep 

 in the whorl, reaching 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 . 



To decide whether an insecticide can be profitably applied, examine fields of corn 

 grown for grain when a few tassels begin to show. If 50 percent or more of the 

 plants have some aphids (a few heavy) and corn is under stress (as from low soil 

 moisture, fertility, disease, etc.), treatment is justified. If growing condi- 

 tions are good, continue to watch the infestation; if 15 percent or more of the 

 plants become heavily loaded with aphids, then 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, applications 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 grain, 

 ensilage, or stover when using malathion. 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. Seed producers may prefer to use either diazi- 

 non or phorate (Thimet) as granules at 1 pound per acre of actual insecticide if 

 corn is still in the late whorl stage. Use phorate only on male-sterile corn to 

 avoid potential hazards to detasselers . 



European corn borer egg laying is about complete in northern sections, and some 

 borers are beginning to tunnel into stalks . Insecticide effectiveness is greatly 

 reduced once the borers leave the whorl and enter the stalk. Treatments should 



