Unfortunately, it may be too late to get through the corn with a cultivator by the time 

 you find the rootworms . If you think the rain did seriously reduce the effectiveness of 

 your planting-time treatment, information from our 1968 corn rootworm control demonstra- 

 tions may help you decide on whether to make a basal application. 



First, 1968 was a year for optimum results from planting-time treatments. We had no 

 tieavy rains between planting time and rootworm egg hatch. We applied diazinon to 1/2 

 jf each plot as a basal application. Our results from 8 fields showed that a planting - 

 time treatment plus a basal application yielded 1-1/2 percent more corn than the planting - 

 time application alone. Under many conditions (including those of 1968), this gain 

 rfould not justify the added expense. But with the heavy rains that came before rootworm 

 3gg -hatch this year, making a basal application could produce much better results this 

 /ear. If you feel certain your field will be heavily infested with rootworms, if you did 

 lave heavy rains, the 1968 data may help you make a decision now, as you should recover 

 at least the 1-1/2 percent in yield as in 1968 and most likely considerably more with 

 this year's rainfall. 



Ihe potential for European corn-borer infestations is still uncertain. Corn-borer develop- 

 nent this year parallels that of 1956, when we had one of our most-severe, first-generation 

 infestations. Moth emergence is similar to that of 1956, egg-laying is a little later this 

 /ear, and the corn about 5 to 10 inches shorter. Thus, borer survival may be slightly lower 

 than in 1956. This year, we have also had more borers die in the pupal stage before they 

 could emerge as moths. In southern Illinois, emergence is complete and egg-laying will soon 

 De over. Examine the most-advanced fields now for possible treatment. Only a very small 

 percentage of the fields are involved. 



[n south-central Illinois, emergence is almost done and about 5 to 20 percent of the moths 

 ire yet to emerge. Egg -laying should be complete by June 20 to 25. On the east side of 

 :he state, a few fields of the most-advanced corn will be involved. On the west side, 2 

 ;o 4 percent of the fields might have economic infestations. The next 7 to 10 days will 

 letermine the importance of corn borer to the early corn. Continue to examine the most- 

 idvanced fields carefully. 



vlthough the threat of economic damage from first-generation borers is not great in south 

 md south-central Illinois, the survival rate may be high enough to cause damage later on. 



~.n central Illinois, about 10 to 30 percent of the moths are yet to emerge. Egg-laying has 

 just begun, and it will continue for the next 2 weeks or a little longer. Much depends on 

 he temperatures at night. If those temperatures remain high, the moths will deposit their 

 ;ggs quickly and egg-laying will be over. Cooler nights will mean that the egg-laying will 

 :ontinue for a longer time, and about 5 to 10 percent of the fields will develop borer prob- 

 .ems . Observe the most-advanced corn until the last few days of June. 



n north-central and northern Illinois, 20 to 45 percent of the moths are yet to emerge. 

 ji occasional egg mass can be found. Egg-laying will continue into late June and early 

 uly. Observe the most-advanced fields carefully, starting about June 20. 



o determine the need for treatment, measure the tassel ratio. Dig up a plant and measure 

 rom the bottom of the plant to the tip of the longest leaf. Split the plant and find the 

 eveloping tassel. Measure from the bottom of the plant to the tip of the tassel. Divide 

 he tassel height by the plant height and multiply by 100. If the tassel ratio is 50 or 

 jver and if 75 percent or more of the plants have corn-borer feeding on the whorl leaves, 

 ihe field should be treated--but not until the tassel ratio is at least 35, preferably 40 

 o 50. If there is corn-borer feeding in the whorl, the percent of plants required to 

 ustify treatment can be reduced with higher tassel ratios. 



