-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. 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 car- 

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

 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 pro 

 vide good control of the corn borer. Parathion has a 12-day waiting period between • 

 treatment and harvest. 



It is possible that many fields will have light first- generation infestations, but 

 these fields will supply a great number of moths. Second- generation borer numbers 

 could be intense in late fields. 



Corn rootworm . Most rootworms found this week were very small, but a few half- 

 grown worms were found as far north as Oregon. If you suspect a rootworm problem 

 and you used no insecticide as a band at planting, examine roots and soil now. 

 Hatch has not yet reached its peak, and even a few worms per plant at this time 

 means greater numbers later. 



Apply cultivation treatments now. Apply granules to the base of the plants. Cover 

 by cultivation. The insecticides suggested for basal treatments are BUX, Dasanit, 

 Dyfonate, or phorate (Thimet) . Use the rate of 1 pound of actual chemical per acre.. 



Corn blotch leaf miner . This maggot tunnels in the leaves of corn, making irregular 

 white longitudinal galleries on the leaves. Damage is not important and no control 

 is necessary. 



ALFALFA INSECTS 



Spotted alfalfa aphid . These yellow aphids with black spots feed on the lower 

 leaves and stems of the alfalfa plant. They inject a toxin into the plant. Small 

 dead spots which enlarge rapidly appear in heavily infested fields. Dry weather 

 usually accentuates the damage. 



The apids migrate into Illinois from the southwest and were found in Champaign 

 County this week. Every year, some are found in Illinois. 



Demeton (Systox) is preferred and can be used once per cutting and no closer than 

 21 days before harvest or pasture. Apply at 1/4 pound per acre. It is every ef- 

 fective as a systemic. 



Use 1 pound of malathion, 1/2 pound of diazinon, or 1/4 pound of parathion per 

 acre as an emergency treatment. Read precautions on labels. Malathion can be 



