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College of Agriculture 



University of Illinois 



and Natural History Survey, Urbana, Illinois 



tate / County / Local Groups / U. S. Department of Agriculture Cooperating 



FOR IMMEDIATE RELEASE 



May 24, 1968 



ILLINOIS INSECT, DISEASE, AND WEED SURVEY BULLETIN NO. 11 



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

 ease, and weed situation (fruit and commercial vegetables excepted) , along with 

 suggested, abbreviated control measures . Each individual should check his own 

 fields to determine local conditions. TflE UBRAHV OF TMF 



MAY ; 



INSECTS 



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Forage Insects 



WBVaSIY OF ILUNOtt 



The alfalfa weevil situation is about the same as it was a week ago. Damage is 

 severe in some unsprayed, uncut fields, but where the first crop has been harvested, 

 the second growth is growing rapidly. The big change this week is the great in- 

 crease in parasitism by a wasp, one that apparently migrated into Illinois with the 

 weevil. Parasitism in several fields varied from 22 to 78 percent, averaging 

 47 percent for all fields examined. 



If you want to see these parasites, select large larvae and place them in a jar 

 with some alfalfa. After a few days, they will build a lace-like netted globe-- 

 the cocoon or shell. In some of these globes, you will see a green worm or pupa; 

 in others, there will be a tiny, brown, seed-like pupa--this is the cocoon of the 

 wasp parasite. 



The total effect of this parasitism cannot be assessed as yet. Parasitized larvae 

 do not die in the worm stage; they die in the pupal stage. Although the larvae 

 feed to maturity, they are not as ravenous as the healthy worms. Furthermore, 

 parasitized larvae pupate earlier in life, cutting down on their total consumption 

 of alfalfa. 



A question has been raised as to the advisability of spraying, since sprays might 

 kill the parasites. If a field is about ready to harvest, cut it. If the plants 

 do not show signs of growth in 2 or 3 days and weevil larvae are numerous and are 

 feeding heavily, spray it. If the plants are growing, you may be able to avoid a 

 spray application. 



Variegated cutworms are abundant in clover fields in the southern half of the state. 

 These grey- to-black worms have a series of white-to-yellow, diamond- shaped dots 

 down their backs. They are usually found in trash on the ground during the day. 

 At night, they feed heavily on the lower leaves of plants and new shoots. Thus, 

 the canopy of leaves on top are untouched, camouflaging the damage that is taking 

 place. When the crop is cut, the worms hide under the bales or windrows. In- 

 fested fields take on a brown appearance after hay removal, as the new shoots are 

 being devoured. Apply 1-1/2 pounds of carbaryl (Sevin) per acre to the stubble 

 after the first crop has been removed. 



