HL: Corn Rootworm Management Strategies for Long-Term Success

Corn rootworm (CRW) has adapted to decades of management strategies and continues to be destructive. These adaptations are part of why diverse management practices and careful planning are key for long-term success. Corn hybrids with newer trait technology options like the Durastak^™ trait stack give farmers important tools for long-term corn rootworm management, particularly where adapted corn rootworm species have been observed.

SH1: Why is Corn Rootworm a Problem?

Corn rootworm is the most destructive corn pest in the United States and costs growers more than $1 billion annually in reduced grain yield and control measures. They cause damage in multiple ways:

• 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.
• If not controlled, adults breed and lay eggs in the soil that can endanger future corn crops.

SH2: What do I need to know about corn rootworm adaptations?

Northern corn rootworm (NCRW) can exhibit extended diapause. This means NCRW eggs have genetically adapted to remain dormant in the soil for more than one winter before hatching. Instead of hatching after one winter as normal, eggs can remain viable for two or more years.

Western corn rootworm (WCRW) has developed a “soybean variant” in some areas (mainly Illinois and Indiana). This means that adult WCRW beetles with this adaptation can lay eggs in soybean fields, which then emerge the following year if corn is planted.

SH3: What are the best strategies for long-term CRW management?

Corn rootworm 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 corn rootworm, but careful planning and hybrid selection are key to building a sustainable, multi-year management plan. A multi-year, field-by-field corn rootworm management plan that uses multiple methods of control in different years is a key best practice to help stay ahead of this pest, protect yield, and reduce potential for resistance.

Step one is to understand whether and how much CRW pressure is present in fields through scouting and/or beetle trapping. Once CRW pressure level is understood, the following management options can be considered independently or in combination as part of a multi-year integrated management plan:

• Crop Rotation: Rotate to non-host crops like soybeans to break up CRW’s normal lifecycle. Adapted variants of CRW, known as western CRW variant or northern CRW with extended diapause, have changed their lifecycles to overcome single-year rotation (Figure 2). Be aware if these adaptations are present locally and research their impact on rotation effectiveness.
• CRW traits:  Rotate between hybrids with multiple modes of action (MOA) like Duracade^® (2 MOA) and Durastak (3 MOA) trait stacks, providing three powerful Bt protein for CRW control.
• Soil-applied insecticides: Force^®6.5G Force Evo, or Opello^® insecticides can help with larvae control.
• Foliar-applied insecticides: Warrior II with Zeon Technology^® for adult beetles may help minimize silk clipping and reduce egg laying.

Corn rootworm management plans should rotate different corn rootworm control methods in different years to help minimize the adaptation of corn rootworm to one technology. The plan may need to change each season, depending on pressure, but having it in place gives growers a head start.

SH4: A few key tools for CRW management

Durastak Trait Technology

The Durastak trait stack is an important tool for fighting corn rootworm because it’s first triple Bt protein trait stack designed specifically for corn rootworm control. By combining three distinct, proven Bt proteins, Durastak traited hybrids bring a new level of diversity to rootworm management. This can help result in stronger and more consistent control across a wide range of pressure levels and environments. In field trials, Durastak trait technology has provided twice the nodal root protection compared to older traits (Figure 3). Better root protection improves standability and provides a stronger root system to support nutrient and water uptake during critical growth stages, which supports yield potential.

Opello Insecticide Technology

Opello is an insecticide that provides strong control of CRW. This liquid, at-planting formulation is smooth and easy to work with, compatible with a wide range of starter fertilizers and can be tank-mixed into open application systems. Opello delivers a strong defense against corn rootworm feeding, resulting in healthier, stronger roots.

CruiserMaxx Corn 1250 Seed Treatment

CruiserMaxx^® Corn 1250 seed treatment is available for select hybrids and is designed to offer additional root protection. Trials comparing treated and untread seed in seven locations showed reduced feeding damage at most sites (Graph 1).

SH5: How to build a long-term corn rootworm management plan

Your plan will depend on your particular situation. A good place to start is whether you’re planting first-year corn or multiple-year corn.

How to manage corn rootworm in first-year corn crops

• -If the Western CRW variant or Northern CRW extended diapause variant are not present, consider using a non-CRW traited hybrid, such as a Viptera^® hybrid, that provides broad-spectrum control of above-ground pests.
• -If other soil insects are present, consider adding soil-applied insecticide.
• -Western CRW variant or Northern CRW extended diapause variant are present, consider using at least a dual-mode of action traited hybrid or soil-applied insecticide.

How to manage corn rootworm in multiple-year corn crops

• -Select dual mode of action traited hybrids featuring a unique Bt protein such as Duracade or Durastak traited hybrids.
• -Continually scout for adult beetles each year and consider a foliar insecticide when needed to minimize silk clipping and reduce female egg laying.
• -Conduct root digs every year to monitor CRW larvae pressure. If root feeding begins to increase, use a Durastak traited hybrid the following year for an additional mode of action.
• -A seed treatment such as CruiserMaxx Corn 1250 may help provide additional nodal root protection.

SH6: A CRW Management example

The Scenario

A field that was previously planted with soybeans will now be planted with corn.

The Risk

Possible presence of extended diapause or the western CRW variant could lead to damage and yield loss.

What to consider

• If adapted CRW species are not present, you could use a non-CRW traited hybrid and consider using Force or Opello soil-applied insecticide to help control larvae.
• If adapted CRW species are present, consider a CRW traited hybrid or a non CRW traited hybrid with Force or Opello soil-applied insecticide.
• If you don’t know if adapted CRW species are present, consulting an agronomist can help assess your risk level.

SH 7: Key Takeaways

1. Long-term corn rootworm management requires a multi-year, whole-farm approach due to species adaptations and crop management factors.
2. Work to strike a balance between control, yield protection and resistance management.
3. Effective management will require the integration of multiple control measures, not a singular technology.