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FOR IMMEDIATE RELEASE July 31, 196^ 



INSECT SURVEY BULLETIN NO. 16 



This is the sixteenth in a series of weekly "bulletins 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 is designed to forewarn people in Illinois 

 of impending changes in insect activity and to suggest abbreviated control meas- 

 ures. These reports indicate only general trends. Each individual should check 

 his own fields to determine local conditions. 



Corn borer : From k-0 to 75 percent of the first-generation "borers have 

 now pupated, and 2 percent of them have already emerged as moths. These moths 

 are beginning to deposit eggs on late corn. Pupation and emergence, although 

 slightly later than last year, are earlier than in some other years. Also first- 

 generation corn "borer populations this year were about half as great as those of 

 last year. 



Fall armyworms , varying in size from newly hatched to mature, are abun- 

 dant in some late fields of both sweet and field corn in south-central and south- 

 ern Illinois. Control measures in field corn are -questionable, as the corn will 

 probably grow away from the damage. Furthermore, by the time the infestation is 

 found, the worms have usually burrowed deep into the whorl, where it is extremely- 

 difficult to reach them with any insecticide. In sweet corn, 1 l/2 pounds of DDT 

 or Sevin per acre will control the small worms when infestations are discovered 

 early. After the worms are large, there is no use to attempt control unless they 

 are migrating from the tassel to the ear. 



Do not use DDT on corn to be fed as ensilage, fodder or stover. 



True armyworms have matured rapidly, and most of them have pupated. The 

 few that remain will not be of major concern. 



Corn earworm control information is being requested by seed producers, 

 since earworms can cut across the tops of the kernels, making them unfit for seed. 

 This damage may occur if the earworm infestation is as intense as is expected. 

 Use DDT or Sevin as earworm sprays when eggs are found on silks, usually on late 

 corn. Use Sevin if the corn is to be used for ensilage, fodder or stover. 



Corn leaf aphids are plentiful in some fields. As is true of earworm, 

 seedsmen are the ones most interested in aphid control, but some cash-grain farmers 

 are also interested. Definite information on damage is meager. We know that a 

 severely infested plant may be barren and that heavy infestations can cause light- 

 weight ears. But we can not give a good rule of thumb on how large the infesta- 

 tion should be before treatment will be profitable. 



The tendency toward barrenness varies greatly and is influenced by hy- 

 brid, planting rate, moisture, fertility and perhaps other growth factors. Some 

 studies have shown that an average of kO percent of the plants severely infested 

 by aphids were barren. That is, if 10 of 100 plants in a field are literally 

 loaded with aphids, four of them, or k percent, will be barren. However, this 

 figure varies tremendously with different hybrids. In counting infestations, do 

 not include sucker plants, as they are commonly infested. 



