You can also control a resistant northern corn rootworm problem by growing a crop 

 other than com for 2 years and following with corn for no more than 2 years. 



Corn leaf aphid populations continue to remain low. South of State Highway 9, 

 populations are declining. North of Highway 9, aphids are present but are not 

 abundant except in a few fields. In general, fields just now tasselling are aver- 

 aging between 2 and 80 percent of the plants with a few aphids; occasional plants 

 have light to moderate numbers. Insidious flower bugs, which resemble a miniature 

 chinch bug, are still numerous in corn and are feeding on the aphids. A few para- 

 sitized aphids can also be found. Some lady beetles, syrphid fly maggots, and 

 aphis lions are present and are eating aphids. 



No one can accurately predict whether these aphid populations will increase or 

 decrease, but the next 2 weeks will determine the outcome. Currently, aphid popu- 

 lations are considerably lower than they were a year ago. Also, soil moisture is 

 ample in most areas. Thus, aphid injury should not be as pronounced as last year. 



Early treatment is best. If corn is still in the whorl stage, if 50 percent or 

 more of the plants have some aphids (a few heavy), and if the corn is under stress, 

 then treat immediately. Treatment is also justified in corn in the late whorl 

 (a few tassels showing) -to -pollinating stage if 15 percent or more of the plants 

 are heavily loaded with aphids (blackened). After pollen shed, aphid populations 

 usually decline, and most of their damage has already been done. Treatments after 

 pollen shed are of little value unless the corn is under severe stress. 



Spray treatments by ground or air with 1 pound of malathion or diazinon per acre 

 will control the aphids. When using malathion, allow 5 days between treatment 

 and harvest for grain, ensilage, or stover. There is no waiting period between 

 treatment and harvest for grain when using diazinon, but allow 10 days to elapse 

 before making ensilage or stover. If corn is still 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. 



Emergence of second-generation European corn borers has reached its peak in the 

 southern sections; the first moths emerged this week in the central section; pupa- 

 tion ranges from 10 to 20 percent in the northern sections. Check late-maturing 

 fields (late whorl-to-early silk stage) now in the southern sections, after August 5 

 in the central section, and after August 12 in the northern sections for egg masses. 

 Apply treatments at first egg hatch if there is an average of one or more egg masses 

 per plant. Use 1 pound of actual diazinon, or 1 1/2 pounds of actual carbaryl 

 (Sevin) , per acre as granules or sprays. Granules--not sprays--are best if the 

 treatment is applied by air. When using diazinon, allow 10 days before making 

 ensilage or stover; carbaryl has no waiting period. 



The general picture for second- generation corn borers is not good, neither is it 

 devastating. Damage is expected to be greatest in the northwest and west sections. 

 From 1 to 12 percent of the cornfields in the state will have more than 5 mature 

 borers per plant by October 1. On the average, yield is reduced 1 percent for 

 each second-generation borer per stalk. The loss is primarily due to broken stalks 

 and dropped ears. The table on page 3 summarizes our predictions of the expected 

 second-generation corn borer populations for each area, with the exception of the 

 southwest section. 



