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Corn Insects 



Black cutworms are still damaging some cornfields. Continue to check fields and 



watch for cut, wilting, or missing plants and the presence of worms. If you find 



most of the worms between 1 1/2 and 2 inches long, it is probably too late for 



treatment, since these worms will stop feeding and pupate in a day or two. 



If control is necessary, apply 5 pounds of toxaphene, 2 pounds of carbaryl (Sevin) , 

 2 pounds of diazinon (granules preferred and cover by cultivating) , or 1 pound of 

 trichlorfon (Dylox) per acre- -directed as a spray at the base of the plants in a 

 narrow 6- to 8 -inch-wide band. 



For best results, use at least 20 gallons of water per acre, and cultivate or 

 rotary hoe immediately to incorporate the spray deposit. Cultivation is preferred 

 over hoeing. Results will depend on soil moisture and rain immediately after 

 spraying. If conditions remain dry, the worms will be down several inches in the 

 soil and control will be poor. 



Corn rootworms are expected to begin hatching this week. If you suspect or know 

 that you have a resistant rootworm problem and you did not use a phosphate or 

 carbamate insecticide at planting time, apply it now . Use granules at the base 

 of the plants and cultivate them in. 



The following insecticides have label approval at 1 pound of actual chemical per 

 acre and are recommended for control of resistant rootworms in Illinois: phorate 

 (Thimet) , 0-5555 (Buxten) , diazinon, disulfoton (Di-Syston), and parathion. 



European com borer egg laying and hatch are complete in the southern sections. 

 Peak egg laying occurred this week in the central and south- central sections, but 

 egg laying will continue for another week or ten days. A few of the most advanced 

 fields (45 inches or taller from ground level to the tip of the tallest leaf) may 

 be damaged in this area. Treatments may begin this week. In north-central and 

 northern sections, peak egg laying will occur during this week (June 18) and next 

 week (June 25). Treatments, if needed, should be applied during the last week of 

 June (north- central section) or the first week of July (northern section) . In 

 general, borer development is ahead of corn development; except for the occa- 

 sional, rapidly growing, advanced fields, damage should be light. 



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

 ratio of the field and count the percent of plants with recent whorl leaf feed- 

 ing. 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 mul- 

 tiply by 100. Tli is figure is the tassel ratio. If the tassel ratio is at least 

 55 (preferably 40 to 45) and at least 75 percent of the plants show whorl feeding, 

 then 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. 



Flea beetles are still feeding on corn. Damage is most severe on newly emerging 

 corn. Corn over 6 to 8 inches tall will usually outgrow damage. If feeding is 

 heavy and plants are being killed, apply 5/4 pound of carbaryl (Sevin) or 1 1/2 

 pounds of toxaphene per acre as a band spray over the row. Carbaryl will also 

 control thrips . 



