FARMS WITH CONTINUOUS CORN 



Northern and western corn rootworm populations increase rapidly in fields where 

 corn is grown for 3 or more years in succession. The beetles emerge in late July 

 and August, feed on silks and pollen, and deposit eggs in the soil. The eggs hatch 

 into larvae the following June. The larvae feed on the corn roots and by early 

 August, the corn begins to lodge. 



Until recently, aldrin or heptachlor (as soil insecticides applied at or before 

 planting) provided excellent protection. However, in 1962, northern corn rootworms 

 highly resistant to aldrin and heptachlor appeared. By 1965, there were individual 

 problem fields in almost every county in the northern half of Illinois. This trend 

 continued in 1966, and the extent of the resistance problem increased. By 1967, 

 failures to control rootworms were common in the northern half of Illinois, and 

 corn lodged in many fields where corn had been grown for 3 or more years continu- 

 ously. At present, if you have grown corn for 3 years or more in succession in the 

 field and if there were lots of green beetles in the fresh silks during August, you 

 probably have resistant northern corn rootworms. 



In 1967, western corn rootworm attack caused severe lodging and yield losses in 

 many fields in Mercer County and neighboring counties. This rootworm species is 

 now present in all counties north and west of a line from Quincy to Peoria to Bel- 

 videre, and an occasional specimen could be present in ever) 7 county in the north- 

 ern half of Illinois. Furthermore, all western corn rootworms in Illinois are 

 highly resistant to aldrin and heptachlor. In 1968, commercial damage from this 

 rootworm may occur in Hancock, Henderson, Mercer, Rock Island, Whiteside, Lee, 

 Bureau, Henry, Knox, McDonough, Peoria, Stark, Fulton, and Warren counties. 



Viewing the extent of the population and the resistance to aldrin and heptachlor 

 of both the northern and western corn rootworms, we can assume that all fields 

 (particularly those in the northern half of Illinois) planted to corn for 3 or more 

 consecutive years could have moderate to severe lodging from rootworm attack in 

 1968. Although the use of aldrin or heptachlor may provide satisfactory control 

 in some fields, attempts to control corn rootworms with these two, previously effec- 

 tive soil insecticides will meet with failure in the majority of cases. Therefore , 

 farmers, particularly those in the northern half of Illinois, who have fields that 

 are to be planted to corn for the third consecutive year or longer should consider 

 some program other than the conventional use of aldrin or heptachlor to control 

 northern and western corn rootworms . 



Unfortunately, there is no insecticide presently available that will control root- 

 worms on all dates of planting when applied at planting time. Therefore, a crop 

 rotation may be the easiest method for corn rootworm control; grow some other crop 

 in the field for 2 years. When rotating to control resistant corn rootworms, use 

 a crop other than soybeans in 1968 if you have used aldrin or heptachlor annually 

 for 5 or more years (including 1967) . If you have applied aldrin or heptachlor 

 annually for several years, but not in 1967, you can plant soybeans in 1968. 



Research entomologists of the Illinois Natural History Survey have shown that pho- 

 rate (Thimet) , BUX ten (0-5553), and diazinon granules applied in a 7-inch band 

 ahead of the press wheel to late-planted corn will control the rootworms that hatch 

 in late June and early July. Phorate and BUX ten applied to mid- season plantings 

 usually last long enough to provide a reasonable degree of root protection during 

 rootworm attack in late June and early July. No insecticide used at planting on 

 early-planted corn has given practical rootworm control. 



