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COLLEGE OF 

 AGRICULTURE 

 UNIVERSITY OF 

 ILLINOIS AT 

 URBANA-CHAMPAIGN 

 AND NATURAL 

 HISTORY SURVEY 

 URBANA, ILLINOIS 



MSECT WEED & PLANT DISEASE SURVEY BULLETIN 



OTE/COUNTY/LOCAL GROUPS/U.S. DEPARTMENT OF AGRICULTURE COOPERATING 



FOR IMMEDIATE RELEASE 



AUG 19 1371 



UN1V- - ILLINOIS 



No. 20, August 13, 1971 



This is the last in this series of weekly bulletins . We have tried to provide a gen- 

 eral look at the insect, weed, and plant disease situation (fruit and commercial veg- 

 etables excepted) , along with suggested, abbreviated control measures. Each individual 

 should check his own fields to determine local conditions . 



INSECTS 



CORN INSECTS 



Fall armyworms . They continue to attack late-maturing corn as well as grain sorghum, 

 particularly in the southern half of the state. These dark-brown to dull-green worms 

 feed in groups of corn plants scattered over the field. After tasseling, these worms 

 often infest the ears, feeding on the kernels similar to earworm. 



Treatment is justified in fields in which 20 percent or more of the plants are in- 

 fested. Before applying insecticides, be sure the worms are still present and that 

 most of them are not more than 1-1/4 inches long. When they reach about 1-1/2 inches, 

 they are mature; at that size they stop feeding, drop to the ground, enter the soil, 

 and pupate. 



European corn borers . The emergence of the second-brood moths is essentially complete 

 now, with emergence reaching over 90 percent in the northern section this week. Based 

 on the first -generation populations, south-central and western Illinois are the areas 

 most likely to have a high number of second -generation borers. Field observations in- 

 dicate that egg- laying will be spread over the next two or three weeks in central and 

 northern Illinois. The number of egg masses and newly hatched borers still remains 

 low in southern Illinois. At any one time, egg counts may not approach the economic 

 level of 100 egg masses per 100 plants , but cumulative counts over a month may be much 

 greater. 



It is difficult to determine when control measures are feasible for the second brood. 

 Overall, we anticipate a noticeable infestation of second-generation corn borers in 

 late corn in many areas of Illinois. Late-maturing fields should be checked for the 

 presence of the borer eggs. Generally, these will be found on the undersides of any 

 of the upper five to seven corn leaves. 



To determine whether treatment is necessary, look for egg masses or whorl feeding. If 

 the average is one or more egg masses per plant, apply an insecticide after a few eggs 

 have hatched. If the corn is in the whorl stage and if 75 percent or more of the 

 plants are showing recent whorl feeding, apply carbaryl (Sevin) or diazinon granules. 

 Aerial sprays on tasseled corn are effective; but on whorl-stage corn, aerial appli- 

 cations should be granules not sprays. Use 1-1/2 pounds of carbaryl (Sevin), 1 pound 

 of diazinon, or 1/2 pound of parathion per acre. Allow 10 days for diazinon and 12 

 days for parathion between application and silage removal. Parathion should be ap- 

 plied only by experienced applicators . No waiting period is required for carbaryl. 



