-2- 



Corn rootworm adults are feeding on silks in many cornfields throughout the state. 

 The tan or pale -green northern rootworms, 12-spotted southern ones, and yellow- 

 and-black (often striped) western rootworms all feed on silks. The western corn 

 rootworm was found for the first time in Brown County this week. In the primary 

 rootworm problem area (the northern half of the state) , as many as 5 or more 

 beetles per silk were observed in some fields this week. Adult emergence varies 

 from 10 to 40 percent in these fields, so adult populations will increase as the 

 beetles continue to emerge. In most of these problem fields, lodging is already 

 noticeable and root damage is severe, due to root pruning by the larvae. 



When beetles are numerous, they can interfere with pollination. The injury will 

 probably be more severe in medium- and late-maturing fields, since adult root- 

 worms are likely to be higher in these fields during the critical pollinating 

 period. 



Treatment for adult rootworms is justified if there are 5 or more per silk, and 

 if not over 50 percent of the plants have silked. Sprays of carbaryl (Sevin) , 

 diazinon, or malathion at 1 pound of actual insecticide or 1/4 pound of methyl 

 parathion per acre are effective. Methyl parathion should be applied by expe - 

 rienced applicators only . Allow 5 days between treatment and harvest for mala- 

 thion, 10 days for diazinon, and 12 days for methyl parathion; carbaryl has no 

 waiting period. Sprays of malathion, methyl parathion, and diazinon will also 

 control corn leaf aphids, while carbaryl will not. 



We have been receiving calls from farmers who have not previously had rootworm 

 problems. Most such problem fields had received an aldrin or heptachlor treat- 

 ment that did not control the rootworms. Rootworm resistance to aldrin and 

 heptachlor has now become widespread in Illinois; hence, these insecticides can 

 no longer be depended on for rootworm control. In general, the phosphate and 

 carbamate insecticides used this past spring for the control of resistant root- 

 worms are providing satisfactory results. Within the next week or two, it would 

 be wise to check your corn (particularly continuous corn) for rootworm damage and 

 for the presence of adult beetles, if you have not already done so. 



You can best determine the need for a rootworm control program for next year by 

 making an estimate of the adult rootworm population at this time. Make a count 

 of the average number of beetles per plant when the corn is in full silk. An 

 average of 5 to 10 or more adults per plant is probably enough to cause economic 

 losses in 1969, if the field is planted to corn again. Although not fool proof, 

 this is the best, current rule of thumb we can give you for predicting rootworm 

 problems for next year. 



Notify your local county Extension adviser about severely damaged fields, espe- 

 cially if you have had failures with the organic phosphate or carbamate insecti- 

 cides used for the control of resistant rootworms. Also, report any fields of 

 first-year corn that have been bothered by rootworms. 



Second-generation European corn borer moth emergence is well under way in southern 

 sections, and eggs are being laid. Emergence is just beginning in the central 

 section. Pupation ranges from 15 to 30 percent in the northern section. Now is 

 the time to check late-maturing fields for egg masses and whorl feeding in the 

 southern section. Wait about a week in the central section, and about 2 weeks in 

 the northern section. Treat whorl-stage corn if 75 percent or more of the plants 

 show recent whorl feeding. Treat tasseled corn if the egg masses per plant average 



