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COLLEGE OF 

 AGRICULTURE 

 UNIVERSITY OF 

 ILLINOIS AT 

 URBANA-CHAMPAIGN 

 AND NATURAL 

 HISTORY SURVEY 

 URBANA, ILLINOIS 



NSECT WEED & PLANT DISEASE SURVEY BULLETIN 



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



FOR IMMEDIATE RELEASE 



No. 5, April 16, 1971 



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 fihpuld check_his own 

 fields to determine local conditions. 



MAY - 6 1971 



INSECTS 



FORAGE INSECTS 



UNIVERSITY OF ILLINOIS 



r-r MOD4(\|A.rM0.MPAIGri 



Alfalfa weevils . The cool weather is slowing larval development, egg hatch, and 

 alfalfa growth. However, adult weevils are present and continue to deposit eggs. 

 An extended period of warm weather in southern and south- central Illinois could 

 bring about a sudden hatch and a rapid build-up of larvae, with accompanying dam- 

 age. Treatments may be justified in an occasional field this coming week south 

 of Highway 13. Last week, larval populations south of this line ranged from 1 to 

 6 per sweep (about 20 per sweep is considered an economic infestation) , with 20- 

 to 80-percent of the plants showing slight tip feeding. One field had 55 larvae 

 per square foot, but the number was considerably less in most fields. Feeding 

 damage and larval populations are hardly noticeable north of Route 15. Depending 

 on weather conditions, we would expect treatments in the south-central area to be 

 warranted within ten days to two weeks and two to four weeks in the central section. 



As you examine alfalfa, the yellowish, newly hatched larvae (about 1/20-inch long), 

 with shiny black heads, can be found feeding within the folded leaves and buds of 

 the plant terminals. Occasionally, an almost -mature larva may also be found. These 

 are green with a white stripe down their back. 



Watch all fields closely from now on. Our egg surveys show that some fields nave 

 a fairly high concentration per square foot. Populations of this insect vary 

 greatly in fields only a short distance apart, so every field must be evaluated 

 individually. Treatment with an insecticide is justified when 25 percent of the 

 tips show feeding and larvae are present. Do not apply insecticides unless they 

 are needed. 



The insecticide recommendations are: 



1. Commercial applicators . Apply 1/2 pound per acre of methyl parathion or azin- 

 phosmethyl (Girth ion) for good results. Use azinphosmethyl only once per cutting. 

 Do not harvest for 15 days after treatment with methyl parathion, or 16 days for 

 azinphosmethyl. Wear protective clothing. 



2. Persons not equipped with protective clothing . Use: (1) Imidan at 1 pound per 

 acre; (2) a mixture of 3/4 pound of malathion and 5/4 pound of methoxychlor per 

 acre; (3) a mixture containing at least 1/2 pound of diazinon and 1 pound of 



