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FOR IMMEDIATE RELEASE June 7, 1963 



INSECT SURVEY BULLETIN NO. 8 



This is the eighth 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 forevarn 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. 



Wireworms have been more abundant in corn fields this year than for the 

 past several years. Damage has been common in fields where no soil treatments were 

 applied; there has even been some damage where soil insecticides were applied. In 

 most cases where control measures failed the corn was planted deeper than usual, 

 and the insecticide was placed above the seed. Thus the wireworms do not get into 

 treated soil to feed. Also in dry soil the wireworms are farther underground than 

 when moisture is normal. In some cases the granules have not dissolved, but have 

 remained unchanged in dry soil. Also the soil has been cool, reducing volatiliza- 

 tion of the insecticide and thus reducing insecticidal activity. Cool weather, dry 

 soil and deep planting have contributed to control failures. 



If replanting is necessary, broadcast 1 l/2 to 2 pounds of aldrin or 

 heptachlor per acre and disk it into the soil immediately, or apply 1 pound per acre 

 in the row as a band treatment. 



Corn borer pupation is now complete throughout Illinois, and almost 100 

 percent of the moths have emerged as far north as Highway 6. Moths are now lay- 

 ing eggs. If we have warm nights and no storms, all eggs will be deposited within 

 the next 10 days to two weeks. Since most of the moths have emerged in the area 

 with the highest borer populations, wind and rain storms couls kill the moths before 

 they lay many more eggs, thus reducing borer potential greatly. This may already 

 have occurred to some extent. 



Cool nights and calm weather would permit the moths to live, but would 

 delay egg-laying. Such conditions could lead to a severe corn borer infestation 

 in northern and western Illinois, particularly in the triangular area bounded by 

 the Mississippi River and a line from Rock Island to Peoria to Carthage. Here 

 some fields of corn are quite advanced. Observe these fields carefully for the 

 next two weeks. 



Insecticides should not be applied until the tassel ratio is over 35; 

 this will be in about two weeks. To determine the tassel ratio, measure the height 

 of the plant with leaves extended; split the plant open and measure from the tip of 

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

 plant height and multiply by 100. This figure is the tassel ratio. If this tassel 

 ratio is 30 or over and 75 percent of the plants show borer leaf feeding on the 

 whorl leaves, treatment is indicated. Do not treat, however, until the tassel ratio 

 is at least 35 and preferably 40 to k-5. Use 1 pound of DDT, or 1 l/2 to 2 pounds 

 of sevin, as granules, per acre. If spraying, use 1 l/2 pounds of actual DDT per 

 acre, but direct the spray onto the upper third of the plant. Aerial applications 

 should be granules, not sprays or dusts. Follow label precautions in harvesting 

 and feeding treated corn. 



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