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INSECT 



SURVEY 



BULLETIN 



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College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



itate / County / Local Groups / U. S. Department of Agriculture Cooperating 



FOR IMMEDIATE RELEASE 









July 28, 1967 



INSECT SURVEY BULLETIN NO. 16 



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 



Adult rootworms are present in cornfields throughout the state. In the northern 

 half of the state, an average high of 5 to 10 beetles per plant was observed in 

 some fields. Populations will continue to increase as more beetles emerge. The 

 corn in these fields has already been damaged (usually badly lodged), due to the 

 root pruning by the larvae. The pale-green northern, 12-spotted southern, and 

 yellow-and-black striped western corn rootworm adults all feed on silks. The 

 western corn rootworm was found for the first time in Stark County this week. 

 When numerous, these beetles can interfere with pollination. 



If a field just now silking (25- to 75-percent silked) averages 5 or more beetles 

 per plant, treatment will be profitable. Treatments applied much after 90 per- 

 cent of the field has silked are of little benefit. Sprays of carbaryl (Sevin) , 

 diazinon, or malathion at 1 pound of actual insecticide per acre are effective. 

 Allow 5 days between treatment and harvest for malathion, 10 days for diazinon; 

 carbaryl has no waiting period. Control of adult beetles will reduce egg laying 

 and will result in fewer larvae in the field next year. However, adult control 

 is no guarantee that problems with larvae will not occur in 1968. 



A word to the wise: During the next week or two, you should check your cornfields 

 to determine if a problem with northern corn rootworms is developing . If you have 

 grown com for several years in succession in the field, if you have used aldrin 

 or heptachlor almost every year, if the com is lodged (maybe only spots) , and if 

 there are lots of pale-green beetles (5 to 10 or more per plant on the average) 

 on the fresh silks, you most likely have resistant northern corn rootworms. Approx- 

 imately 10 percent of the cornfields sampled in 1966 had resistant beetles. In 

 the limited area of infestation (western section of Illinois) of the resistant 

 western corn rootworm, make a count of the average number of beetles per plant when 

 the corn is in fresh silk. An average of 5 to 10 or more adults per plant is prob- 

 ably enough to cause economic losses in 1968 if the field will be in corn again. 



If a resistance problem is apparent in your field and the field is to be replanted 

 with corn, plan on applying a phosphate or carbamate insecticide next year. Pre- 

 liminary results in Dr. Ralph Sechriest's research plots indicate that basal treat- 

 ments cultivated-in at or near lay-by time give better results than planting-time 

 treatments . 



