3. For the common Illinois rotation (which includes soybeans, corn, and grains), 

 continue to plant soybeans as you have in the past. The future of this sug- 

 gestion depends on research and survey data. 



CORN SOIL INSECT SITUATION 



Western corn rootworms : In 1968 they were found, with the exception of 8 counties, 

 throughout the area of Illinois north of a line from Pittsfield (Pike County) , to 

 Lincoln (Logan County) , to Kankakee (Kankakee County) . In 1969 , they may spread 

 to most of the counties north of a line from St. Louis to Danville. In Mercer and 

 adjoining counties, many second-year cornfields were damaged in 1968; in 1969, 

 many fields of second-year corn will be severely damaged in the area north and 

 west of a line from Dixon to Peoria to Stronghurst (Highway 116) , and extended to 

 the state boundaries. Second-year cornfields will be damaged more than others, 

 but not all of them will be severely affected. 



All western corn rootworms in Illinois are resistant to the commonly used soil 

 insecticides aldrin and heptachlor; they will no longer control this insect. 



The northern corn rootworm , although found throughout Illinois, is most abundant 

 north of Highway 56 (Pittsfield to Springfield to Decatur) , and is often a pest 

 in fields if corn is grown for 3 or more years continuously in the same field. 

 Under some conditions, we have seen second-year corn damaged by northern corn 

 rootworms. Although it is not common, this does occur. 



Even though northern rootworms are not a general pest south of this line (Pitts- 

 field to Springfield to Decatur) , they do damage corn severely in central localized 

 areas, such as bottomland, where corn is grown as a continuous crop. 



Northern corn rootworm populations increased in 1968. Despite this, weather con- 

 ditions favored root regrowth, and many fields were able to recuperate from severe 

 root pruning and produce a good yield. Therefore, damage was less apparent in 

 1968 than in 1967. The population of corn rootworm beetles was greater in August, 



1968, than in either 1966 or 1967. Thus, the threat of damage is greater for 



1969. To further complicate matters for 1969, resistance to aldrin and heptachlor 

 has increased to such a degree that these two insecticides no longer give practical 

 control of northern corn rootworms in the majority of cornfields. 



Seed-corn beetles eat the seed and chew off the sprout during germination. There 

 were a lot of these pests this past year. Quite often, aldrin, dieldrin, heptachlor, 

 and lindane soil or seed treatments failed to control them. Seed-corn maggots 

 hollow the seeds prior to their germination. In at least two instances, resistance 

 to aldrin, chlordane, dieldrin, heptachlor, and lindane were confirmed. 



In 1968, attacks by these two seed pests reduced stands from a few hundred plants 

 per acre in some fields to as many as several thousand plants per acre in others. 



Wireworms , cutworms, white grubs , grape colaspis , and others are still controlled 

 by the use of aldrin or heptachlor, even though these chemicals can no longer be 

 relied on to control rootworms, seed-corn beetles, and seed-corn maggots. 



CONTROL OF RESISTANT ROOTWORMS, RESISTANT SEED INSECTS, AND GARDEN SYMPHYLANS 



A crop rotation may be the easiest method for controlling resistant corn rootworms. 

 To hold populations of northern corn rootworms at low levels, do not grow corn for 

 more than 2 years successively in any rotation. In western corn rootworm areas, 



