March 9, 2007

Requirements Differ for ECB and Corn Rootworm Bt Products

IRM Refuge Requirements

Following are the IRM requirements for Bt rootworm corn (A) and Bt European corn borer corn (B).

If you are growing a Bt corn stack that has genes for both corn borer and rootworm, you must follow the IRM for rootworm program (A). This would include such products as Agrisure CB/ LL/RW, Agrisure GT/CB/LL/RW, Herculex XTRA, and YieldGard Plus.

A. IRM for transgenic corn hybrids active against corn rootworm.

 

1. Growers must plant a structured refuge of at least 20% non-Bt rootworm corn that may be treated with insecticides (e.g., seed treatments, liquid or granular) as needed to control corn rootworm larvae.
2. Growers will not be permitted to apply corn rootworm labeled insecticides to the refuge for control of insect pests (either rootworm beetles or other insects, e.g., western bean cutworms, grasshoppers, etc.) while adult corn rootworm are present unless the Bt rootworm field is treated in a similar manner.
3. Refuge plantings may be blocks in or adjacent to Bt rootworm cornfields or in-field strips.
4. External refuges must be planted adjacent to Bt rootworm fields.
5. When planting the refuge in strips across a field, refuges must be at least six rows wide for YieldGard Rootworm and YieldGard Plus, or at least four rows wide for the Agrisure RW products, Herculex RW and Herculex Xtra. It is preferable to have wider strips, such as 12 consecutive row-wide strips.
6. Insecticides for control of corn rootworm larvae may be applied to the refuge area.

In addition, the refuge must be planted in similar ground as the Bt corn for rootworm. If the Bt corn for rootworm is planted in ground that was corn the previous year, so must the refuge. General management of the Bt corn for rootworm and the refuge should be similar, e.g., planting dates, irrigation, fertility programs, etc.

B. IRM for Bt corn hybrids active against European corn borer.

 

1. On each farm, growers may plant up to 80% of their corn acres with Bt corn. At least 20% of their corn acres must be planted with non-corn borer Bt corn and treated only as needed with insecticides. Decisions to treat the refuge must be based on economic thresholds. Conventional Bt products (liquids or granules) must not be used on the non-Bt refuge.
2. Plant the non-Bt corn refuge within, adjacent to, or near the Bt cornfields. The refuge must be placed within 1/2 mile of the Bt field, preferably within 1/4 mile.
3. If refuge is established as strips in a field, the strips should not be narrower than four rows.

General management of the Bt corn for European corn borer and the refuge should be similar, e.g., planting dates, irrigation, fertility programs, etc.

Transgenic corn hybrids (i.e. Bt corn hybrids) resistant to insects and the insect resistance management (IRM) requirements for growing these hybrids are familiar to most Nebraska farmers. However, with Bt corn for rootworms, Bt corn for corn borers, and Bt stacks for rootworm and corn borer, it can be a little difficult to keep the Bt corn hybrids and their respective IRM programs straight, especially at planting time when weather, breakdowns and other interruptions can make it necessary to modify original plans. This article will review the current IRM programs and encourage growers to fully comply with IRM requirements.

A variety of BT transgenic corn hybrids are resistant to European corn borer (and some other caterpillars), corn rootworm or both. Trade names for transgenic corn hybrids that are only resistant to European corn borer and a few other caterpillars are AgrisureTM CB/LL, Agrisure GT/CB/LL, Herculex® I, and YieldGard® Corn Borer. Trade names for transgenic corn hybrids that are only resistant to corn rootworm are Agrisure RW, Agrisure GT/RW, Herculex RW, and YieldGard Rootworm. Trade names for transgenic corn hybrids resistant to BOTH European corn borer and corn rootworm are Agrisure CB/ LL/RW, Agrisure GT/CB/LL/RW, Herculex XTRA, and YieldGard Plus.

Use the requirements listed at right to plan your refuges and ensure your fields are compliant.

More Information

Additional information concerning Bt corn and resistance management can be obtained through the following web addresses: 

• Agrisure Products — http://www.agrisuretraits.com/Agrisure/AgrisureServlet/PsAgrisureLogin
• Herculex products — http://www.dowagro.com/herculex/steward/

More corn insect pest management information is available through several UNL resources: 

• UNL Entomology Web site
• Local UNL Extension offices
• UNL NebFact, "Resistance Management for YieldGard Rootworm Bt Corn" (NF594)
• UNL NebGuide, "Resistance Management for European Corn Borer and Bt Transgenic Corn: Refuge Design and Placement" (G1668) .
• The UNL AgBiosafety Web site

A Final Word

Compliance with IRM requirements is very important to the success of the overall IRM program, the goal of which is to prevent resistance to Bt toxins in Bt transgenic corn from developing in target insect pests (European corn borer and corn rootworm). Initially, compliance was measured through the use of grower surveys; however, now random field visits are also conducted to monitor compliance.

For example, sites are selected from the pool of farmers who bought Bt corn. The producer would be contacted and a date scheduled for a field visit by an independent agent, such as a consultant. Planting records are examined, refuge fields are measured for size and distance from the Bt field, and plants are tested for the expression of the Bt toxin. If found to be significantly out of compliance, the farmer is provided resistance management educational materials, aided in developing a resistance management plan and will be revisited the following year. If the farmer is found to be out of compliance the second consecutive year, the farmer will be denied sales of the product the next year.

Producers have the most important job in maintaining the continued effectiveness of Bt corn and limiting the development of resistance. They should follow resistance management practices and report any possible product failure to their seed dealer or local extension person. With continued IRM compliance we will hopefully preserve Bt corn as an effective pest management tool well into the future.

Tom Hunt
Extension Entomologist, UNL Haskell Ag Lab, NEREC
Bob Wright
Extension Entomologist, Lincoln
Keith Jarvi
IPM Assistant, NEREC, Norfolk