Cooperative Extension Service, University of 

 a . t . . - Illinois College of Agriculture in Cooperation With 

 the Illinois Natural History Survey and U.S.D.A. 



FOR IMMEDIATE RELEASE August 26, I966 



INSECT SURVEY BULLETIN NO. 19 



This is the nineteenth and last weekly bulletin for this year on the general 

 insect situation in Illinois (fruit insects excepted), prepared by entomologists of 

 the University of Illinois College of Agriculture, Illinois Natural History Survey 

 and cooperating agencies; it reports general trends in insect activity and suggests 

 abbreviated control measures. Each individual should check his own fields to deter- 

 mine local conditions. 



Green cloverworms have been abundant this past week in western and north- 

 western Illinois soybean fields, where they have been devouring leaves. Most of the 

 worms will mature this coming week. Defoliation of early beans may not affect yields, 

 since the crop is now maturing rapidly; but if these worms begin to eat pods, which 

 they rarely do, then control may be required in these fields. On the other hand, 

 defoliation of late-maturing beans by these worms may be quite important, as pods 

 are just setting and beginning to fill. Thus control of the worms may be warranted 

 to prevent loss of leaves. As a rule of thumb, the minimum average population re- 

 quiring control is six per linear foot of row. To determine the field average, shake 

 the plants over the row center and count the worms in several places in the field. 



Use 1 l/2 pounds of toxaphene per acre or one pound of carbaryl (Sevin) 

 per acre to control these pests. When using toxaphene, do not apply within three 

 weeks of grain harvest. Do not use plants or crop refuse for livestock feeds. Do 

 not apply toxaphene to fields adjacent to fish-bearing waters. There is no time 

 limitation on the use of carbaryl. 



Alfalfa webworms and two-spotted mites can still be found in soybean fields, 

 but populations generally decrease as the beans mature. 



Grasshoppers are feeding on soybean pods in some fields. In general, num- 

 bers are low, but control with 1 l/2 pounds of toxaphene or 1 pound of carbaryl per 

 acre can be justified in an occasional field to prevent pod damage. Follow the re- 

 strictions listed above when applying toxaphene to soybeans. 



Corn borer populations may be increasing in the southern third to half of 

 Illinois. We have no counts to prove this, but we have reports from some areas of 

 moderate to heavy infestations by second-generation borers. It is difficult to fore- 

 cast the intensity of a third generation. The cool weather this past week may have 

 slowed the growth of the second -generation worms. They will now prepare for winter, 

 and only a few of them will pupate to form a third generation. 



Northern corn root worm adults are still found in many cornfields. Tnese 

 yellowish -brown or green beetles are no longer concentrating on the silks, which 

 have turned brown, but are flying from plant to plant. An occasional late field may 

 show some silk feeding by these beetles. It is too late to consider treatments with 

 insecticides, as the possible damage to pollination has already occurred. 



Fall armyworms damage is evident in a few late-maturing cornfields. The 

 dull green to brown, smooth-skinned worms feed in the whorl of the plant, causing 

 a ragged appearance. Later they feed on the ears. In many cases the larvae have 



