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Both the yellow- to-tan to pale-green northern corn rootworm adults and the yellow- 

 and-black-striped western corn rootworm adults (northwestern section) will be found 

 emerging and feeding on fresh silks during the next several weeks. These insects 

 can reduce pollination. Particularly watch late-planted fields as these fields are 

 most likely to reach the early-silk stage at the time of peak adult rootworm popula- 

 tions . 



Treatment is justified if there are 5 or more beetles per plant and if not over 

 50 percent of the plants have silked. Sprays of carbaryl (Sevin) , malathion, or 

 diazinon at 1 pound of actual chemical per acre or 1/4 pound of actual methyl para- 

 thion per acre are effective. Methyl parathion should be used by experienced appli- 

 cators only. Allow 5 days between treatment and harvest for malathion, 10 days for 

 diazinon, and 12 days for methyl parathion. Carbaryl has no waiting period. 



First-generation corn borers are pupating and emerging as moths in the southern half 

 of the state. Check late-maturing fields for whorl feeding in late July and early 

 August. 



Pupation is just beginning in the northern half of the state, and it will be another 

 week before the first moths begin to emerge. Borers ranged from small to nearly 

 full grown, with most of them half to two-thirds grown. They are now beginning to 

 tunnel into stalks, and most of them will enter the stalk within the next week. 

 Check late-maturing fields for whorl damage or egg masses in early to mid-August. 



Second- generation infestations in late-maturing fields can be handled in the same 

 way as the first-generation problems. If 75 percent or more of the plants have 

 whorl- leaf feeding, apply carbaryl (Sevin) or diazinon granules. If the corn has 

 tasseled, look for egg masses. If the average is 1 or more per plant, apply an in- 

 secticide after a few eggs have hatched. 



Commercial applicators may prefer to use parathion at 1/2 pound per acre. Sprays by 

 air or with high-clearance ground equipment are effective on tasseled corn. Allow 

 10 days between treatment and harvest when using diazinon and 12 days for parathion. 

 Carbaryl has no waiting period. 



Corn leaf aphids are slowly increasing in numbers, but populations are still light. 

 Individual aphids and a few colonies were observed in about 1 to 5 percent of the 

 plants in fields in the central section. Many fields of corn are now coming into 

 tassel, and with aphid numbers low it is doubtful that these fields will have a 

 serious problem. This is particularly true in areas that have ample soil moisture. 

 In areas with low soil moisture, however, a late buildup of aphids could still be 

 serious. In general, it does not appear that the corn leaf aphid will present as 

 severe a problem as it did in 1966 and 1968. It is still early for reliable pre- 

 dictions, and the next week or two will more definitely determine the situation. 

 Continue to check fields that have not yet reached the early tassel stage for aphid 

 buildup. 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. Methyl parathion should be applied by experienced applicators 

 only. 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. 



