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Corn Rootworm Management Using Previous Year Beetle Counts
Corn growers should base the need for using a rootworm soil insecticide on the abundance of rootworm beetles in corn fields during late summer of the previous crop. When the adult population averages one or more beetles per plant, the potential for larval root damage in these fields the next summer is sufficient to warrant control.
However, if the previous year the field scouted was corn following any crop other than corn, the threshold (beetles per plant) is lower. The ratio of female to male beetles in first-year corn is usually higher than in continuous corn. As a consequence, the threshold for determining whether to rotate away from corn or to use a soil insecticide may be as low as 0.5 beetle per plant, i.e. one beetle per two plants.
Proper calibration, placement, and incorporation of rootworm soil insecticides will improve the likelihood of good control. The soil insecticides are labeled for application in a 7 inch band ahead of the planter press wheels. Some can be applied in the seed furrow and this would be the preferred method of application in fields where wireworm problems are also known to occur. All insecticides should be lightly incorporated with spring tines or drag chains mounted behind the planter units.
Granular soil insecticides will give about 50 to 75% control of corn rootworm larvae. This degree of control is adequate to prevent economic levels of larval damage in most fields.
For More Information see Insect Guide at http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm
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