FOR IMMEDIATE RELEASE June 23, i960 



BISECT SURVEY BULLETIN NO. 10 



This is the tenth in a series of weekly 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 : Cool, rainy weather during this past week has changed the 

 corn borer situation. Some moths undoubtedly were killed by rain and wind. Some 

 eggs were laid on weeds and small grains where no corn was suitable for egg-laying. 

 In other situations moths remained inactive during the cool nights but were laying 

 eggs in the corn fields during cloudy days. Egg-laying will be concentrated in the 

 most advanced fields, and damage may become noticeable within the next few weeks. 

 Observe these most advanced fields regularly during the next two weeks. 



In a triangular area from Quincy to Decatur (Highway 36) to St. Louis, 

 50 to 80 percent of the plants in less than 10 percent of the fields have fresh 

 corn borer feeding on whorl leaves, with 25 to 100 egg masses per 100 plants yet to 

 hatch. Corn in these most advanced fields has just now reached the stage of develop- 

 ment where corn borer will begin to survive. This is the week in this area to de- 

 cide whether or not to treat. 



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. 



In the area from Highway 36 north to about Highway 17, egg-laying is well 

 under way but remains low. Examine the most advanced fields carefully this week. 

 Treatment, where needed, should start about July 1. 



North of Highway 17, egg- laying has started and will now progress rapidly; 

 treatment, where needed, should probably start soon after July 1. This may be the 

 area where a few advanced fields could be hit hard. 



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

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

 ing, arrange two or three nozzles over the row to cover the uppper 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. 



Black cutworms : Damage to corn is now being reported from most areas of 

 the state and will continue to increase for the next few days. —Observe low spots 

 carefully for damage. If stands are still worth saving, apply 1/2 pound of dieldrin, 



