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Corn rootworm adults are increasing in abundance in cornfields, and there are more 

 to come before emergence is complete. The tan or pale-green northern rootworms, 

 the yellow and black-striped western ones, and the 12-spotted southern rootworms, 

 all feed on silk. In most fields, pollination is complete and silk feeding is no 

 longer important. We observed a few heavily infested fields of western rootworms 

 (15 to 20 or more beetles per plant) , where the adults were feeding on the silks 

 as well as skeletonizing leaves and feeding on brace roots. In these fields, the 

 root pruning by the larvae was so severe that some corn plants were dying. The 

 western corn rootworm infestations appear to be most severe in fields of second- 

 year corn, while northern corn rootworm infestations seem most severe in fields 

 where corn has been planted for 3 or more years in succession. 



In most fields, treatment with insecticides at this time will not be profitable. 

 But in late fields, where pollination may still be affected by silk feeding, or 

 in those where adults are extremely numerous and are damaging ear tips, treatment 

 may still be justified. Treatment for adults is recommended only if there are 

 5 or more beetles per ear, and if not over 50 percent of the plants have silked. 

 Sprays of carbaryl (Sevin), diazinon, or malathion at 1 pound of actual insecti- 

 cide or 1/4 pound of methyl parathion per acre are effective. Methyl parathion 

 should be applied by experienced applicators only . Allow 5 days between treat- 

 ment and harvest for malathion, 10 days for diazinon, and 12 days for methyl para- 

 thion; carbaryl has no waiting period. Sprays of malathion, methyl parathion, and 

 diazinon will also control corn leaf aphids, while carbaryl will not. 



Do not expect a single insecticide application for adult control to significantly 

 reduce the number of larvae that will be present in the field next year. Migra- 

 tion of the adult beetles from adjacent fields and prolonged emergence will pro- 

 vide sufficient eggs to cause economic problems in 1969, if the field is planted 

 to corn again. However, it is possible that two or more applications may kill 

 enough adults now to reduce larval numbers next year. 



European corn borer moths are now present in most areas. In north-central and 

 northern Illinois, egg laying will not really be underway for several days yet; 

 egg laying has just begun in central Illinois. First -generation populations were 

 low in these areas. Severe second- generation damage is not expected. 



However, many fields in south- central Illinois were infested by first-generation 

 borers. Second-generation moths are numerous in this area, and egg laying will 

 progress rapidly during the next 2 weeks. Many fields now in the late-whorl stage 

 will be favored by the moths for egg laying. Watch such fields closely; some late- 

 planted cornfields may be severely damaged. 



If you find small worms in the whorls of 75 percent of these plants, an application 

 of an insecticide will be justified. In the more-mature fields, count egg masses. 

 If there is an average of 1 egg mass per plant, insecticide applications will be 

 profitable. Apply insecticides at first egg hatch. 



Use either 1-1/2 pounds of carbaryl (Sevin), or 1 pound of diazinon, as a granule 

 or spray. On whorl-stage corn, aerial applications should be granules, not sprays. 

 Aerial sprays on tasseled corn are effective. Allow 10 days to elapse before making 

 ensilage or stover when using diazinon. Carbaryl has no waiting period. 



