Corn Rootworm Management in 2021

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Corn Rootworm Management in 2021

11/16/2020
The most destructive corn pest in the United States is corn rootworm. It costs growers more than $1 billion annually in reduced grain yield and control measures.Corn rootworm eggs are laid the previous year and overwinter in the soil. Larvae hatch and begin feeding on the corn roots in late May and early June.This root feeding usually lasts for about 3 weeks before the insect pupates. Root feeding can cause reduced water and nutrient uptake and potentially a pathway for disease introduction to the corn plant. If root feeding is severe enough, it can cause the plant to lodge and be more susceptible to wind damage.This lodging can cause challenges at the time of harvest.The insect emerges as adult beetles in early July with peak emergence occurring around the beginning of August.These adult beetles feed on pollen, corn leaves, soft kernels, but cause the most damage feeding on silks. Silk pruning can interfere with corn pollination causing reduced kernel set.

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Scouting and taking beetle counts in July through August help estimate the level of corn rootworm larval presence and potential damage one might expect the following year, if the field will be corn again the following year. The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) surveys beetle counts annually throughout the state and in 2020 found the highest state average numbers of beetles in five years. The south-central region of the state saw the largest increase from the recorded 0.5 beetles per plant last year to 1.3 per plant in 2020. The southwest and central regions saw higher numbers of beetles as well. The threshold for adult beetle populations is 0.75 beetles per plant and if thresholds are at that level or higher, potential for significant yield loss may occur if the pest is not controlled.

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Multiple tactics can be used to control corn rootworm. The highest levels of larval feeding and beetle counts have been found in fields with many years of continuous corn. One of the most effective methods of control is crop rotation. Rotation will help to break up the cycle and reduce corn rootworm populations.Planting corn hybrids with multiple modes of action of the corn rootworm traits will assist in control. The use of an effective soil-applied insecticide at planting has proven to be effective at controlling rootworm larvae. Lastly, controlling beetles can be accomplished with a foliar applied insecticide. This application can reduce egg laying and reduce populations the following year. With the presence of high levels of rootworms, multiple strategies may be needed for adequate control.

For additional information on management strategies that best fit your operation to control corn rootworm, contact your Crop Specialist at Insight FS.

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