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Control of corn rootworm (CRW) beetles is important for preserving the yield potential of the current crop and for reducing insect 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. An excellent tool, in addition to diligent monitoring, to help determine when insect populations may reach damaging levels is the online resource www.insectforecast.com.
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, and beetles are clipping silks to within a 1/2 inch of ear tips and pollination is not complete.1
Action Thresholds for Suppressing Egg Laying. Thresholds vary by state and planting density. In general, if adult beetle populations equal or exceed 1 beetle per plant, adults have reached the treatment threshold, and larvae could cause significant lodging and/or yield loss the following season.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.
1 Bissonette, S.M., Pataky, N.R., Mafziger, E.D., et al. Field Crop Scouting Manual. X880e. University of Illinois Extension. 2 Hodgson, E.W. 2008. Western corn rootworm. Utah State University Extension Pests Fact Sheet ENT-109-07PR. 150710152050