Adult Corn Rootworm Beetle Management Considerations

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.

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Adult CRW Beetle Scouting and Thresholds

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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.

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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

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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.

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Best Management Practices for Root Protection

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  • Rotate to a non-host crop such as soybeans to break the CRW life cycle. Periodic rotation provides a number of benefits in addition to effective CRW control.
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  • Plant SmartStax® RIB Complete® Corn Blend products that provide dual mode-of-action (pyramided) B.t. traits and deliver excellent CRW protection.
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  • If rotation or SmartStax® RIB Complete® Corn Blend products are not acceptable options, consider using soil-applied insecticides in combination with seed products that do not provide B.t. protection from CRW larvae.
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  • Due to resistance concerns, planting single-mode-of-action technologies such as Genuity® VT Triple PRO® products or Genuity® VT Triple PRO® RIB Complete® Corn Blend products is not recommended when less than satisfactory control of CRW larvae has been previously observed.
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Summary

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Regardless of which CRW management strategy is implemented for root protection, growers should consider adopting the following support activities to maximize success.

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  • Scout the crop regularly throughout the growing season collecting relevant information regarding insects throughout their life cycle. Electronic tools available to use as decision aids include Genuity® Rootworm Manager App which provides a custom risk assessment based on planting history and recommended response tactics to corn rootworm pressure throughout the season. More information is available at www.genuity.com/rootwormmanager. Also, to assist in determining when insect populations may reach damaging levels is an online resource at www.insectforecast.com.
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  • Use foliar insecticide rescue treatments for CRW adult control, according to established economic thresholds.
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  • Control volunteer corn and weedy escapes in rotational crops. These plants may attract CRW beetles and encourage concentrated egg-laying within the non-host crop.
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  • Read, follow, and understand, the IRM Grower Guide for all B.t. technologies prior to planting and observe all refuge requirements.
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