INSECT 



SURVEY 



BULLETIN 



3 m\ 



v *ttw%. 



tate 



County 



Local Groups 



College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



U. S. Department of Aarjcultu^ 5fORfl[e rating 



JUL 3 1968 



FOR IMMEDIATE RELEASE 



UNiVtRilY OF ILLINOIS 

 June 28, 1968 



ILLINOIS INSECT. DISEASE. AND WEED SURV EY BULLETIN NO. 16 



This series of weekly bulletins provides a general look at the insect, plant dis- 

 ease, and weed situation (fruit and commercial ve g e table*uj£XG^tgd) , along with 

 suggested, abbreviated control measures. Each individual snomW MJM his own 

 fields to determine local conditions. in, „ . 



Jul. g 2 ms 



insects Htoatwir flr nutam 



Corn Insects 



Northern and western corn rootworm eggs continue to hatch, and in some fields of 

 continuous corn in the northern half of the state an average of 30 larvae per 

 plant are already present. Counts of 100 or more per plant will be common in 

 problem fields within the next week or two. There is extreme variation in egg 

 hatch and size of the worms from field to field. The worms scarify the surface 

 and tunnel into the roots. They particularly like the tender, more succulent, 

 newly-forming brace roots. By late July or August severely damaged plants will 

 tip over. 



To find rootworm larvae, dig up a 6-inch-square area of soil about 6 inches deep 

 around the corn plant. Examine the soil by breaking up the clods and sifting 

 the soil through your fingers. Rework the soil several times. Then tear up and 

 split the roots, watching the debris which falls for additional larvae. Another 

 method of checking for rootworm larvae is the use of a salt solution. Mix a pound 

 of crude salt or table salt in a gallon of water. Place the soil and roots into 

 this solution and stir vigorously. The rootworm larvae will float to the top and 

 with care can be sorted from the foam and debris and counted. Do not dump the 

 salt solution in the field. 



If you suspect or know you have a rootworm problem (10 to 15 per plant or more 

 justifies treatment) and you can still get a cultivator through the field, it 

 still may not be too late (particularly in the northern section) to obtain some 

 benefit. However, for best results the applications should have been made a week 

 or two ago when eggs were just beginning to hatch. Further delay now in treat- 

 ment will result in less effective control since damage is already occurring. 



We recommend 1 pound of actual diazinon, disulfoton (Di-Syston) , or phorate (Thimet) 

 per acre as a basal treatment off the cultivator. The insecticide is directed at 

 the base of the plant and the cultivator throws dirt over the chemical. 



First -generation European corn borer infestations are generally light in the prob- 

 lem area of west -southwestern, west -central, and northwestern Illinois. In the 

 most advanced corn between 5 and 40 percent of the plants were infested this week. 



