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FOR IMMEDIATE RELEASE July 2k, 196k 



INSECT SURVEY BULLETIN NO. 15 



This is the fifteenth in a series of weekly bulletins on the general insect 

 situation in Illinois (fruit insects excepted), prepared by entomologists of the Uni- 

 versity of Illinois College of Agriculture, Illinois Natural History Survey and coop- 

 erating agencies. It is designed to forewarn people in Illinois of impending changes 

 in insect activity and to suggest abbreviated control measures. These reports indi- 

 cate only general trends. Each individual should check his own fields to determine 

 local conditions. 



Armyworms have been the topic of conversation this week in many areas of 

 northern Illinois. There were reports of infestations from the Melvin-Sibley area in 

 Ford county on the east to Monmouth on the west and north to the Wisconsin border. 

 Most of the infestations occurred in the eastern half of the state, however. Except 

 for the northern tier of counties, the armyworm problem should subside this week, and 

 by August 1 a worm will be hard to find. 



The main questions this week concerned how mature the worms are, how much 

 longer they will feed, how abundant their natural enemies are, whether there will be 

 another generation, and what kind of weather favors the armyworm. 



Fat armyworms, 1-1 A to l-l/2 inches long, have finished feeding. They will 

 burrow into the ground and pupate at any moment. Armyworms 3 A inch to an inch long 

 will feed for three to five more days. 



Tiny worms — l/8 to 1/2 inch long — ordinarily feed for two weeks, but natural 

 enemies are building up in many areas and these small worms will probably be killed by 

 disease or parasites before they can damage plants. Parasites, both wasps and flies, 

 and a virus disease were beginning to kill a few large armyworms this week. 



Brown heavy -bodied armyworm moths will begin to emerge in about two weeks. 

 Some will remain and deposit eggs. The worms that hatch will die from parasitism or 

 from disease. These parasites and the virus disease prevent armyworm outbreaks in 

 successive generations in the same area and the same year. Some moths will also mi- 

 grate northward out of Illinois. 



These armyworms have been feeding on corn, grassy weeds, oats, and other grass 

 crops. In some instances they have been feeding heavily on corn silks. Extensive 

 silk feeding during pollination could be serious. If the entire plants are stripped 

 before the ears are filled out, yields could be decreased. If only the lower leaves 

 are stripped, the damage will not be serious. Armyworms will not eat good-sized leg- 

 ume plants or soybeans but will eat small legume seedlings. Cool, damp weather favors 

 armyworms, but humid weather is unfavorable. 



Time for maximum benefit from treatment is almost past. Therefore each 

 field must be judged on its own merits — size of the worms, type and location of feed- 

 ing, and extent of parasitism and disease incidence should be determined before treat- 

 ment is even considered. 



Do not panic because you find some armyworms. It takes loads of armyworms 

 to do serious damage. Also, in many instances grassy weeds like foxtail, now present 

 in fields, will feed the worms until they mature. 



