Managing Corn Rootworm

• Corn rootworm (CRW) has adapted to decades of management strategies and continues to be destructive.
• The DuracadeViptera^™ trait adds a different tool to the toolbox for CRW management.
• Diversity in management practices is key for long-term success in managing CRW.

Corn rootworm impact on corn crops

Corn rootworm (CRW) is the most destructive corn pest in the U.S. and costs farmers more than $1 billion annually in reduced grain yield and control measures. Larvae feed on roots, resulting in underdeveloped root systems, reduced nutrient uptake, weak brace roots and lodged corn (Figure 1). Adult CRW beetles can also interfere with pollination by feeding on pollen and clipping silks, resulting in poor ear fill. They also lay eggs in the soil, which endangers future corn crops. Continuous corn and overreliance of a single management practice have expanded resistant CRW populations.

Corn rootworm life cycle

Larval hatch has adapted to extend from late May to mid-June. CRW larvae go through 3 instar stages before pupating when they stop feeding on roots. July is when farmers need to monitor for adults feeding on silks and starting egg lay. Beginning in mid-July, a single adult female can lay up to 500 eggs and create excessive pressure in subsequent years. In continuous corn, farmers should keep adult beetle numbers below the threshold of 1 insect per plant.

Northern CRW eggs can remain dormant for 2 winters, a practice referred to as extended diapause. Once the eggs are laid in a cornfield, they overwinter and remain dormant through the soybean crop, overwinter again and hatch into the next corn crop. As pictured in Figure 2 at bottom left, rotating to nonhost crops disrupts the CRW life cycle. As you'll see in bottom right portion of Figure 2, even in areas where northern CRW exhibit extended diapause and the western CRW is laying eggs in soybean fields, rotation still reduces CRW populations. 

Monitoring corn root damage

Preventing excessive pressure is the key to successful CRW management. In continuous corn, dig several plants to determine if additional control measures are needed for the current cropping year. Studies have shown a 15% to 18% yield loss when one full brace root node is pruned within ½ inch of the base of the plant. Allowing 2 or more nodes to be pruned greatly impacts water and nutrient uptake, potentially resulting in severe lodging and creating a difficult harvest.

Corn rootworm management

CRW is a difficult pest to manage to the point that repeated use of the same single management practice will eventually end in disappointment. There is no silver bullet for CRW, but smart planning and hybrid selection are key to building a sustainable, multiyear management plan. Developing a multiyear, field-by-field CRW management plan utilizing different control methods in different years is an important part of addressing one of the most damaging insect pests to corn and ensuring hybrids reach their full yield potential. Understanding if CRW is currently present in fields through scouting or beetle trapping is an important first step in developing management plans. Once the relative risk of CRW is understood, the following management options can be considered independently or in combination as part of a multiyear integrated management plan:

• Crop rotation: Rotate to nonhost crops like soybeans to break up CRW’s normal life cycle. Adapted variants of CRW, known as western CRW variant or northern CRW with extended diapause, have changed their life cycles to overcome single-year rotation (Figure 3). Be aware of their presence locally and the impact they could have on rotation effectiveness.
• Dual mode of action CRW traits: Use different CRW traits like DuracadeViptera and Agrisure^® Total Refuge Renew^™ that have more than 1 CRW trait.
• Use soil-applied insecticides like Force^® 6.5G insecticide for larvae control.
• Use foliar-applied insecticides like Warrior II with Zeon Technology^® for adult beetle control to minimize silk clipping and reduce egg laying.

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Plans should include the use of different CRW control methods in different years to help minimize the adaptation of CRW to one technology. The plan may need to change each season, depending on pressure; however, having it in place gives farmers a head start.

DuracadeViptera trait helps manage corn rootworm

The DuracadeViptera trait, the most recently registered Bacillus thuringiensis (Bt) CRW trait, expresses a protein that binds differently in the gut of CRW than in any other trait on the market. Additionally, it is always stacked with a second mode of action against CRW, making it a good tool for managing CRW (Figure 4). Golden Harvest^® Agronomy in Action research trials have evaluated the effectiveness of DuracadeViptera across multiple years and found that the trait demonstrated improved root protection (Graph 1) and yield (Graph 2) when used alone or in combination with soil-applied insecticides across many different pest levels.

Select Golden Harvest DuracadeViptera hybrids are now available treated with CruiserMaxx^® Corn 1250 seed treatment for additional root protection. CRW trials across 7 locations showed reduced feeding damage at most sites (Graph 3). Whether trying to protect yield or preserve effectiveness of current management practices, effective CRW management will require the integration of multiple control practices, not a singular technology.

Options for managing low corn rootworm pressure

If little to no previous signs of larval feeding or adult beetle populations have been observed and planting corn is selected for areas with western CRW variant, northern CRW extended diapause or corn following corn, consider using at least 1 of the following management practices:

1. Multiple mode of action CRW-traited hybrids
2. Non-CRW-traited hybrid with Force 6.5G soil-applied insecticide

If planting first-year corn in areas where CRW has not yet been known to have adapted to corn rotation management, consider using a non-CRW-traited hybrid, such as an Viptera^™ Refuge Renew^™ hybrid, which provides broad-spectrum control of above-ground pests. If other soil insects are present, consider adding Force 6.5G soil-applied insecticide.

Options for managing heavy corn rootworm pressure

For fields with historic CRW pressure, a more aggressive management plan may be needed to minimize damage and maximize yield potential.

• Crop rotation: The most effective management strategy is nonhost crop rotation. Consider breaking up the CRW life cycle by rotating to nonhost crops, such as soybeans, in fields with a history of high CRW presence or injury.

• Traited corn hybrids:
  1. If there is no history of root injury on traited hybrids:
     • Use hybrids with multiple CRW traits
     • Scout and consider beetle control with a foliar insecticide to minimize silk clipping and reduce female egg laying
  2. If there is a history of feeding damage to traited hybrid and you’re unable to rotate, use a combination of:
     • Hybrids with multiple CRW traits
     • Soil-applied insecticide with traits
     • Scouting and considering beetle control with a foliar insecticide
     • Seed treatment insecticides

Long-term CRW management requires a multiyear, whole-farm approach. There is an important balance between CRW control, yield protection and resistance management. It is not a one-size-fits-all approach. Effective CRW management will require the integration of multiple control measures, not a singular technology.

Watch this video to hear Syngenta Seeds Technical Agronomy Manager Bruce Battles discuss CRW management and the Golden Harvest Agronomy in Action research being done to help assess management practices.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.