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Control of corn rootworm (CRW) beetles is important for preserving the yield potential of the current crop and for reducing CRW populations in the following season. At high numbers, adults feeding on pollen and silks can interfere with pollination, which can have a direct economic impact on the current crop. Future CRW populations will be affected by the number of adult females currently laying eggs in the field.
Scouting. Monitoring adult beetle populations is key to assessing whether or not insecticide applications are warranted. Weekly scouting for beetles should begin at early tassel and continue through early September. For detailed information on scouting techniques, see the DEKALB® spotlight Adult Corn Rootworm Management found at www.aganytime.com.
Action thresholds for ear protection. In general, treatment with foliar insecticides to control beetles during pollination is warranted when: beetle counts of 5 or more per plant are found, beetles are clipping silks to within ½ inch of ear tips, and pollination is not complete.1
Action thresholds for suppressing egg laying. Thresholds vary by region, planting density and crop rotation. In general, if adult beetle populations exceed 0.5 to 1 beetle per plant, potential for significant yield loss the next season may exist if no control tactics are instituted.2 Insecticide applications should be timed when the proportion of gravid females (females with eggs) reaches 10% of the females collected. If the number of gravid females exceeds 25% then it is likely that significant egg laying has occurred and reduces the chance that adult control will have much, if any, affect on larval pressure and subsequent root damage levels the following season.
Regardless of which CRW management strategy is implemented for root protection, growers should consider adopting the following support activities to maximize success.
1 Bissonnette, S.M., Pataky, N.R., Nafziger, E.D., et al. 2010. Field Crop Scouting Manual. X880e. University of Illinois Extension. 2 Wright. B. 2009. Use of corn rootworm scouting numbers as basis for 2010 production decisions. Crop Watch. University of Nebraska-Lincoln. http://cropwatch.unl.edu/corn-rootworm-7-24-09. Web source verified 06/06/16. 150710152050