Resistance by southern corn rootworms to chlorinated hydrocarbon insecticides like 

 aldrin and heptachlor is common in the southern states, where these beetles origi- 

 nate each spring. It is not surprising that failures with aldrin and heptachlor 

 against this insect occurred this year. 



Reports of rootworm (northern, southern, and western) damage due to a resistance 

 problem continue to filter in. If you used a phosphate or carbamate insecticide 

 at planting time or as a basal treatment at or near layby time, do not expect a 

 100-percent kill of rootworms. Basal treatments are giving better results than 

 planting- time treatments. About 70-percent control is considered average. In 

 fields of high rootworm populations (40 to 150 larvae per hill) , it would not be 

 unusual to find 10 to 40 larvae per hill surviving after treatment. Damage would 

 be apparent in these fields, and it would be impossible to assess the effect of the 

 treatment without an untreated strip for comparison. Conceivably, heavy rainfall 

 could result in failures with these insecticides, since they break down (hydrolyze) 

 more readily when in contact with water. Some areas received heavier- than-normal 

 rainfall in late May and June. It is now too late to attempt to control the lar- 

 vae, but adult beetles can still cause further damage. 



Adult beetle populations will be at their peak in early- to mid-August, feeding 

 on fresh silks. These beetles can interfere with pollination when they are nu- 

 merous. If a field averages 5 or more adult beetles per ear during silking, 

 treatment is justified. For optimum results, the field should be at least 25 

 percent and not over 75 percent silked at the time of spraying. Treatments ap- 

 plied after 90 percent of the plants had silked were not worthwhile. Sprays of 

 carbaryl (Sevin), diazinon, or malathion at 1 pound of actual chemical per acre 

 are effective. Use diazinon if aphids or corn borer are also present, since it 

 is effective against all 3 insects. When using malathion, allow 5 days between 

 treatment and harvest for grain, ensilage, or stover--10 days for diazinon. There 

 is no waiting period for carbaryl. 



Second generation European corn borer moths are emerging in the southern third of 

 the state. Egg laying is progressing rapidly south of a line from Harrisburg to 

 Carbondale . 



In south- central Illinois, moth emergence is just beginning, and pupation is about 

 40 percent complete. In central Illinois, pupation ranges from 10 to 20 percent, 

 while pupation is just beginning in northern Illinois. Lower-than-average tempera- 

 tures have delayed borer development. Moth emergence and egg laying will extend 

 over a 3- to 4-week period in most sections of the state. 



In the southern section, begin checking fields late this week, in the central 

 sections about August 5, and in northern sections about August 12 for the presence 

 of egg masses. The fields most likely to receive the most eggs will be those in 

 the late-whorl to early-silk stage of development. 



Apply treatments at first egg hatch, if there is an average of 1 or more egg masses 

 per plant. Carbaryl (Sevin) or diazinon as granules or sprays are effective against 

 second-generation corn borers. 



Wooly bear caterpillars are feeding on silks in some fields. They snip off the 

 silks similar to a scissors cut. They seldom become numerous enough to cause seri- 

 ous damage, but one report of severe damage has been received. Carbaryl (at 1 1/2 

 pounds per acre) as a spray directed at the ear zone should control the insect. 



