April 2, 2010

The number of Bt-corn hybrid events available is growing, and keeping their respective target pests and insect resistance management (IRM) plans straight can be confusing (see Table 1 for a summary). There also is a new group of hybrids available for 2010 — SmartStax™ Bt corn. We will discuss these new hybrids and review IRM for other Bt corn hybrids available for 2010.

SmartStax™ Bt Corn Hybrids

SmartStax™ is the outcome of a cross licensing agreement and research and development collaboration between Monsanto Company and Dow AgroSciences LLC. Under the terms of the agreement, Dow will market the product as SmartStax. Monsanto will market the products as Genuity™ SmartStax. All other brands will market the product as Genuity™ SmartStax.

The new hybrids will express the following insecticidal proteins: Cry3Bb1 (event MON88017), Cry34/35Ab1 (event DAS-59122-7), Cry1F (event TC 1507), and Cry1A.105+Cry2Ab2 (event MON89034). The proteins will provide the same above- and below-ground insect protection as previously available in Dow AgroSciences’ Herculex® I and Herculex® RW Insect Protection hybrids and Monsanto’s YieldGard VT Rootworm/RR2® and VT PRO contained in Genuity™ VT Triple PRO™ technology; as well as two established weed control systems.

In addition to targeting corn rootworms and the lepidopteran complex, SmartStaxTM hybrids will provide herbicide tolerance to glyphosate and glufosinate based on Roundup Ready® 2 technology from Monsanto and Liberty Link® from Bayer CropScience. EPA approval enables producers in the Corn Belt who use the hybrids to reduce refuge size from 20% to 5%. Cotton Belt producers can reduce their refuges from 50% to 20%. For more information on Smartstax™ hybrids, see the EPA factsheet.

Resistance Management Programs

Hybrids that are resistant to both European corn borer (and a few other caterpillars) and corn rootworm are becoming increasingly popular. All Bt corn hybrids require planting a refuge as part of an insect resistance management (IRM) program. We will review the current IRM programs and encourage growers to fully comply with IRM requirements.

To date, the only change for resistance management in 2010 is with SmartStaxTM corn hybrids, which will have a reduced refuge. All other requirements, such as refuge placement, etc. apply.

Following are the IRM programs 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, follow the IRM for rootworm program (A). Again, the only difference is if you plant SmartStaxTM, where the refuge percentage is 5%.

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., liquid or granular seed treatments,) 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 similarly.
3. Refuge plantings may be in-field strips or blocks in or adjacent to Bt rootworm cornfields.
4. External refuges must be planted adjacent to Bt rootworm fields.
5. Refuges planted in strips across a field must be at least six rows wide for YieldGard rootworm resistant hybrids, or at least four rows wide for the Agrisure and Herculex rootworm resistant hybrids. Wider strips, such as 12 consecutive rows, are preferable.
6. 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 in corn the previous year, the refuge also must be.
7. Insecticides for control of corn rootworm larvae may be applied to the refuge area.
8. 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 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 the refuge is established as strips in a field, the strips should be no narrower than four rows.
4. General management of the Bt corn for European corn borer and the refuge should be similar, e.g., planting dates, irrigation, fertility programs, etc.

The Importance of IRM Compliance

Compliance with IRM requirements is critical to the success of the IRM program, the goal of which is to prevent insect pests from developing resistance to Bt toxins in Bt transgenic corn. Farmers should comply with the IRM requirements to

1. preserve Bt corn as an effective pest management tool well into the future, and
2. continue to have access to Bt corn hybrids.

In the past, compliance was measured primarily through the use of grower surveys; however, monitoring compliance now includes field visits. For example, farmers are randomly selected from the pool of those who bought Bt corn. They are then contacted, and a field visit is scheduled. Planting records are examined, refuge fields are measured for size, configuration, distance from the Bt field, and corn plants are tested for the expression of the Bt toxin. If the farmer is found to be significantly out of compliance, the farmer is provided resistance management educational materials, aided in developing and implementing a resistance management plan, and revisited the following year. If the farmer is found to be out of compliance a second consecutive year, the farmer will not be allowed to buy the product the next year.

The farmer has the most important job in maintaining the continued effectiveness of Bt corn and limiting the development of resistance. This job is following IRM programs and reporting any possible product failure to their seed dealer or local extension person.

Another key item is record-keeping to keep track of what hybrid was planted where on your farm. This will help you avoid making a mistake during the hectic planting season, and help you document your actions, should you be inspected.

Resources

• For more information on this and related topics, see the Corn Insect Management page on CropWatch or contact your local Extension office.
• For more IRM information on European corn borer resistant hybrids, see NebGuide G1668, Resistance Management for European Corn Borer and Bt Transgenic Corn: Refuge Design and Placement 
• For more information on a host of topics concerning Bt corn and biotechnology, visit the UNL AgBiosafety Web page.

Robert Wright, Extension Entomologist
Tom Hunt, Extension Entomologist