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In general, there is a light to moderate number of corn borers in most of the more- 

 mature fields (over half the acreage) throughout the state. Corn borers are also 

 surviving in crops other than corn. Most hollow-stemmed weeds, small grains (like 

 oats), certain vegetables, and even flowers (as well as many other plants) are suit- 

 able hosts for corn borers. A report was received this week of potatoes in a home 

 garden being severely damaged by corn borers. With good survival of this first 

 generation, we could experience severe second-generation corn borer problems in many 

 of the late-maturing fields. 



Corn rootworm larvae are increasing in number as the hatch of overwintering eggs con- 

 tinues - ! Untreated plants in one of our demonstration fields averaged 13 worms per 

 plant. Approximately 4 percent of the larvae have pupated in the central section. 

 Egg-hatch is expected to continue for another 2 to 3 weeks, and the number of larvae 

 will continue to rise during the next week or two- -then level off as more larvae reach 

 the pupal stage. Damage to roots is beginning to show and will become progressively 

 worse over the next 2 to 3 weeks . Rootworm development is about a week later than 

 last year. 



Except for extreme conditions, it is generally too late to apply a basal treatment 

 off the cultivator, since corn plant breakage and root pruning would be too great. 

 The prospects of effective control by broadcasting the insecticides without culti- 

 vation are not good. 



Corn leaf aphids are beginning to appear on corn in the central section. Individual, 

 winged aphids were found on a few plants. These winged females will now give rise to 

 young -producing, small colonies of aphids within a few days. Aphid predators like 

 lady beetles, aphis lions, and insidious flower bugs are present. These predators 

 will feed on the developing aphids. It is too soon to predict the severity of corn 

 leaf aphid infestations. 



Corn leaf aphids suck the juices from the plants causing the ears to be stunted and 

 shriveled. Injury to the plants usually occurs just prior to and during tasseling. 



Early treatment is best. Treatment is warranted when corn is in the late-whorl to 

 early tassel stage and when 50 percent or more of the plants have a light to moderate 

 number of aphids. At the latest, treatment should be made prior to brown silks. 



Spray treatments by ground or air, with 1 pound of malathion or diazinon or 1/4 pound 

 of methyl parathion per acre, are effective. Allow 5 days for malathion, 10 days for 

 diazinon, and 12 days for methyl parathion between treatment and harvest for grain, 

 ensilage, or stover. If corn is in the late-whorl stage, seed producers may prefer 

 to use 1 pound per acre of either diazinon or phorate (Thimet) as granules. To 

 avoid potential hazards to detasselers, use phorate only on male-sterile corn. 



Common stalk borers can still be found in corn plants along the edges of fields. 

 They come from the weeds and grasses bordering on these fields . This is one of the 

 heaviest years on record for stalk borer. Preliminary damage studies conducted 

 last year by Stephen Sturgeon, Survey Entomologist, showed a yield reduction of 37 per- 

 cent for damaged plants, compared to undamaged plants in the same field. Only a small 

 percentage of the total plants are generally infested. By the time the damage is 

 found, the worms are deep in the whorl and control is difficult. It would help to 

 keep weeds and grasses bordering the cornfields well mowed in August and September, 

 thus discouraging stalk-borer moths from laying their eggs for next year's crop of 

 worms . 



