COLLEGE OF 

 AGRICULTURE 

 UNIVERSITY OF 

 ILLINOIS AT 

 URBANA-CHAMPAIGN 

 AND NATURAL 

 HISTORY SURVEY 

 URBANA, ILLINOIS 



«ECT WEED & PLANT DISEASE SURVEY BULLETIN 



iTE/COUNTY/LOCAL GROUPS U.S. DEPARTMENT OF AGRICULTURE COOPERATING 



FOR IMMEDIATE RELEASE 



No. 11, June 12, 1970 



This series of weekly bulletins' provides a general look at the insect, weed, and plant 

 disease situation (fruit and commercial vegetables excepted) , along with suggested, 

 abbreviated control measures . Each individual should check his own fields to determine 

 local conditions. RARY of THE 



INSECTS 



JUN 2 » Vrii 



INOIS 



Black cutworms still rate the "insect of the week" award. However, the worms are 

 maturing rapidly and damage should decline. Check your corn for cut or missing plants -- 

 a sign that the cutworms are at work. If plants are being cut above the growing point 

 and if the worms are larger than 1 inch, the outbreak will be over shortly and the corn 

 will continue to grow. However, immediate treatment is needed if the plants are being 

 cut below the growing point and if many of the worms are less than an inch long. Use 

 a spray- -directed at the base of the plants--of carbaryl (Sevin) at 2 to 5 pounds, 

 diazinon at 2 pounds, toxaphene at 3 pounds, or trichlorfon (Dylox) at 1 pound of 

 actual chemical per acre. It is best to use at least 20 gallons of water per acre 

 and to cover the spray band by throwing soil at the base of the plants with a culti- 

 vator. 



Corn-borer development generally appears to be ahead of the corn, thus lowering borer 

 survival and reducing the threat of serious damage. However, in many areas, the most- 

 mature corn fields may become heavily infested. 



In the southern section of Illinois, egg-hatch reached its peak this week. Most of 

 the corn in that area is too small for borer survival. The tiny borers already present 

 in fields where the corn is less than 40 inches high will die. In many of the fields 

 of 50-inch or taller corn, 75 to 100 percent of the plants are infested. If needed, 

 treatments should be applied now. 



In the central section, moth -emergence is nearly complete and egg- laying is reaching 

 its peak. Treatments, if needed, should be applied during the week of June 21. 



In the northern section, 40 to 60 percent of the moths have emerged and egg-laying is 

 underway. 



To determine the need for treatment, measure the tassel ratio. Dig up a plant and mea- 

 sure from the bottom of the plant to the tip of the longest leaf. Split the plant and 

 find the developing tassel. Measure from the bottom of the plant to the tip of the 

 tassel. Divide the tassel height by the plant height and multiply by 100. If the tas- 

 sel ratio is 30 or over and if 75 percent or more of the plants have corn-borer feeding 

 on the whorl leaves, the field should be treated- -but not until the tassel ratio is at 

 least 35, preferably 40 to 50. The percentage of infested plants required to justify 

 treatment can be reduced with higher tassel ratios . 



