-2- 



To determine the need for treatment, first check the tassel ratio. Dig up a plant 

 and measure 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. 

 This will give you the tassel ratio. If the tassel 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. 



Use 1 pound of actual diazinon in granular form per acre, or 1-1/2 pounds of carbaryl 

 (Sevin) as granules. For spraying, use the same amount of actual insecticide per acre, 

 and direct the spray to the upper third of the plant. Aerial applications should be 

 as granules, not sprays or dusts. Allow 10 days between treatment and the ensiling of 

 corn when applying diazinon; carbaryl has no waiting period. Commercial applicators 

 may prefer to use parathion at 1/2 pound actual per acre, which will provide good con- 

 trol of the corn borer. Parathion has a 12 -day waiting period between treatment and 

 harvest. 



Corn rootworm eggs have begun to hatch. Northern and western corn rootworms are ex- 

 pected to cause moderate to severe damage in fields of continuous corn (three or more 

 years) in the area north of a line from Pittsfield to Springfield to Joliet. 



To determine whether the larvae are present, dig up a corn plant and place the plant 

 and soil on a piece of dark plastic or other material. Sift the soil carefully for 

 the whitish rootworm larvae. Dissect the corn roots to determine if larvae are feed- 

 ing inside the roots. 



Newly hatched larvae are very difficult to find because of their small size. In fields 

 already planted if you find two or more rootworm larvae per plant and if an insecti- 

 cide was not applied at planting time, a cultivator application would be justified 

 now. Apply Bux, carbofuran (Furadan) , Dasanit, Dyfonate, Mocap, or phorate (Thimet) as 

 a basal treatment during cultivation. 



FORAGE INSECTS 



Alfalfa weevils still need watching. The adults and larvae are damaging the new growth 

 of the second crop in some fields recently cut. One field in central Illinois was se- 

 verely damaged by adult weevils. Some fields in southern Illinois have a large number 

 of cocoons on the ground, and the adult weevils will soon be emerging. These newly 

 emerging adults will feed for a week or two before going into summer hibernation. 



Adult feeding damage appears as a "feathering" along leaf margins and may occur in 

 the southern half of Illinois as the pattern of emergence increases. After hay is cut, 

 if the new growth does not show signs of greening up within two to four days, look 

 for the 1/4- inch brown snout beetles in the small green larvae of the alfalfa weevil. 

 One swing of a sweep net over the foliage will give an indication of the adult popu- 

 lation. 



To control the adult weevils and larvae, apply sprays of malathion and methoxychlor 

 (2 to 3 quarts per acre of 4 pounds-per-gallon emulsifiable concentrate) or diazinon 

 and methoxychlor (3 quarts per acre of Alfatox which contains 2.4 pounds per gallon 

 EC). Methyl parathion at 1/2-pound per acre gives effective control of adult weevils, 

 but should be applied only by commercial applicators. Use a minimum of 10 gallons of 

 finished spray per acre on the stubble or 4 gallons by air. 



