J-n7 



FOR IMMEDIATE RELEASE July 1, 19&) 



INSECT SURVEY BULLETIN NO. U 



This is the eleventh in a series of veekly "bulletins on the general insect 

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

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

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

 changes in insect activity and to suggest abbreviated control measures. These re- 

 ports indicate only general trends. Each individual should check his own fields to 

 determine local conditions. 



Corn "borer : In general, corn "borer populations are concentrated in the 

 west half of the state. In a triangular area from Quincy to Decatur to St. Louis, 

 there are a few particularly advanced fields which would profit from treatment. The 

 numbers of fields is less than 1 percent, "but these should be treated immediately 

 if they are to be treated at all. 



In the area between highway 36 and highway 17, corn borer are still laying 

 a few eggs, bu£ in general, even the more advanced fields apparently will have low 

 borer populations and in only a few of the most advanced fields will it pay to 

 apply insecticides. 



In the area north of highway 17, and west of highway 23, 1 to 5 percent 

 of the fields will warrant applications of insecticides. The number of fields that 

 would profit from insecticide treatment varies considerably from one community to 

 another. The fields which are much further along than any other fields in the com- 

 munity have moths concentrating in them and laying eggs. This egg laying, however, 

 should decrease rapidly now. Not only will it pay to control the borers in these 

 fields but with borers concentrated in them, it is an opportunity to reduce the 

 number that will emerge to form a second generation. Treatments in this area should 

 be applied between July h and 10, for best control. 



To determine the need for treatment, examine 50 to 100 plants for signs of 

 borer feeding on the whorl leaves. If 75 percent or more of the plants show recent 

 whorl feeding, check the tassel ratio. Measure from the base to the tip of the 

 plants with leaves extended. Split the plant lengthwise, and measure from the base 

 of the plant to the tip of the developing tassel. Divide the tassel height by the 

 plant height and multiply by 100. Take an average of five representative plants 

 per field. This is the tassel ratio. The corn will warrant treatment if the tassel 

 ratio is 30 or above. Treatment after borers have drilled into the stalk proper 

 will not be effective. 



DDT is still the insecticide most commonly used for corn borer. Apply 

 1 1/2 pounds per acre as a spray or 3/4 to 1 pound per acre as granules. When 

 spraying, arrange two or three nozzles over the row to cover the upper one-third 

 of the plants, particularly the whorl zone. 



Other insecticides approved for use against corn borer include endrin and 

 toxaphene. Ensilage or stover of corn treated with DDT or toxaphene should not be 

 fed to dairy cattle. Endrin may be used in this case, provided label restrictions 

 are followed. ,uv\\#^ 



Black cutworms : Damage reports continue to come in, but thevheaviesx 

 concentrations of this pest seem to have been along the west side of -The state.^\\^ 

 Moderate infestations have occurred in the southeast and extreme north. ,yA* ^ 



