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the northern corn rootworm, and the offspring produced more nearly resemble the 

 western. Therefore within a few years the more severe and resistant western corn 

 rootworm will probably largely replace the northern. A random survey of 10 fields 

 in Mercer County (county most heavily infested with western corn rootworm) a week 

 ago, showed an average of 10.9 western adults per 25 plants, while northern adults 

 averaged 2.6 per 25 plants. The adult western is an aggressive, active insect 

 with a large appetite. One western probably does as much feeding as 2 or 3 north- 

 erns. 



Some fields in Mercer County are averaging 15 to 20 or more western adults per 

 plant. Control is justified when numbers are this high and tip feeding is severe, 

 even though pollination is complete. Control of adults should help to reduce egg- 

 laying, resulting in somewhat fewer larvae next year. However, control of adults 

 will not prevent problems with larvae in 1968 if the field will be in corn again . 

 Sprays of carbaryl, diazinon, or malathion at 1 pound per acre of actual insecti- 

 cide are effective. Commercial applicators may prefer to use 1/4 pound of para- 

 thion per acre. Allow 5 days between treatment and harvest for malathion, 10 days 

 for diazinon, and 12 days for parathion; carbaryl has no waiting period. 



Fall armyworm damage is evident in some late-maturing cornfields. These brown to 

 dull-green, smooth-skinned worms feed in the whorl, giving plants a ragged appear- 

 ance as the leaves emerge. Unless 20 to 25 percent of the plants still have worms 

 less than 1 inch long, treatment is not justified in field corn. For control, 

 apply either 1 1/2 pounds per acre of actual carbaryl or toxaphene as granules. 

 Toxaphene should be used only if the corn is to be used as grain; it should not 

 be used on ensilage corn. Do not apply toxaphene to fields adjacent to fish-bearing 

 waters . 



Special Note to Seed Producers : Seed-corn producers should watch for fall army- 

 worms as well as the corn earworm in late-maturing fields since both feed on tip 

 kernels and scar other kernels from now until harvest . Corn earworm moths in 

 central and northern sections, although still low in numbers, increased this past 

 week. Carbaryl sprays should protect the ears against invasion by these insects, 

 but must be applied before the worms enter the ear. Make the first application 

 when the field reaches full silk and repeat the treatment in 7 days for best re- 

 sults. 



Corn leaf aphids increased in a few late-maturing fields in the central and north- 

 ern sections. In early- and medium -maturing fields, the aphids that were present 

 have about disappeared. In general, the aphid threat is about over for this year, 

 and infestations and injury were much less than last year. 



Soybean Insects 



Populations of green cloverworms are gradually increasing in soybeans. A few para- 

 sitized worms were observed this week. These pale-green worms, with two thin white 

 stripes along each side, strip the leaves but do not attack pods as do grasshoppers 

 and bean leaf beetles. As yet, no serious infestations have been reported but 

 problems could arise during the next few weeks . 



In general, early-maturing beans may escape injury, since if pods have filled, de- 

 foliation is not important. Damage is most severe when defoliation occurs during 

 the period from half -filled pods to mature but green beans. The effect of varying 

 degrees of defoliation on yield reduction in soybeans is largely unknown. 



