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In the west -southwest section the optimum time for treatment is past as borers 

 are already entering the stalk. In the west-central and northwest sections the 

 time for treatment is this week (July 1) . 



To decide whether an insecticide can be profitably applied, measure the tassel 

 ratio of the field and determine the percentage of the plants with recent feeding 

 in the whorl leaves. To determine the tassel ratio, measure the height of the 

 plants with leaves extended; split the stalk open and measure from the tip of the 

 developing tassel to the base of the plant; divide the tassel height by the plant 

 height; and multiply by 100. That figure is the tassel ratio. If the tassel 

 ratio is at least 35 (preferably 40 to 45) and at least 75 percent of the plants 

 show whorl feeding, treatment is justified. 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 granules, not 

 sprays or dusts. Allow 10 days between treatment and ensiling of corn when ap- 

 plying diazinon; carbaryl has no waiting period. Recent label approval has been 

 granted for use of 7 1/2 to 10 pounds of 20 -percent carbaryl granules per acre . 

 Our tests some years ago were with 5-percent granules, but we would anticipate 

 similar control results. 



A report was recei\ r ed of black cutworms damaging waist-high corn in northern 

 Illinois. The recent wet weather in many areas of the state makes conditions 

 favorable for continued cutworm development. On tall corn the worms bore into 

 the stalk just at or slightly below ground level and tunnel up or down in the 

 stalk for a short distance. The leaves of infested plants first wilt and later 

 turn brown. The plant will snap off readily if handled. On small corn the stalk 

 is usually cut off and the plant pulled into the cutworm burrow. There is little 

 that can be done to control the cutworm once corn is laid by. If you can still 

 get a cultivator through the field, an application of 3 pounds of toxaphene, 2 to 

 3 pounds of carbaryl (Sevin) , 2 pounds diazinon (as granules) , or 1 pound of 

 trichlorfon (Dylox) per acre will control small worms. Direct the spray at the 

 base of the plants , using at least 20 gallons of water per acre and cultivate 

 immediately to cover the spray deposit. 



Common stalk borers are feeding in the whorls of some corn plants and the staixs 

 of oats. These whitish-brown, striped worms with a purple band around their 

 middle cause irregular holes to appear in unfolding corn leaves; in oats the heads 

 turn white prematurely. Damage is most common along the edges of fields- - 

 especially adjacent to fence rows, ditchbanks, roadsides, and grass waterways 

 where there was a weed problem out in the field the previous year. Usually only 

 a small percentage of the total plants are infested. Injury is of little con- 

 sequence and by the time the stalk borers are found, it is too late for an in- 

 secticide to be effective. You can lessen the problem for next year by keeping 

 weeds under control in August and September. 



Black and yellow grass thrips (about 1/16 inch) are abundant in the whorl leaves 

 of corn. The thrips rasp the leaf surfaces, leaving silvery patches. Plants are 

 not usually seriously affected and will outgrow the damage. 



Corn leaf aphids are present in the whorl of corn plants in a few fields, partic- 

 ularly in the west-southwestern section. Aphids were also observed on grasses in 

 and bordering cornfields in the central section. These early aphid migrants are 

 winged and will soon move to corn, giving rise to many young aphids. It is still 

 too soon to determine how serious the problem will be in 1968. 



