PRINCIPLES OF RESISTANCE

Principles of Resistance

Bt (Bacillus thuringiensis) corn is an important technology that helps corn growers control damaging insect pests. To preserve the many benefits of Bt corn technology, farmers must implement an insect resistance management (IRM) plan.

Plant a Refuge

Experts agree, and government regulations require, that an effective Bt IRM plan includes the planting of a non-Bt corn refuge to accompany planted Bt corn acres. All Bt corn products require implementation of an IRM program according to the refuge size, refuge distance guidelines and insecticide usage described on this page. Farmers who fail to follow these requirements risk losing access to Bt corn technology.

Why a Refuge?

The purpose of planting a refuge area is to prevent pests from developing resistance to the Bt technology. Insects that feed on the non-Bt crop remain susceptible to Bt technology. In the rare instance that an insect that feeds on the Bt crop survives after feeding on Bt corn, the only insects available to mate with will be Bt-susceptible. This means that the resistance gene will be less likely to be passed along to offspring, preserving the effectiveness of the Bt technology.

Refuge Planting Options

Non-Bt corn refuge can be planted in the ways described below. Refuge configuration options are dependent upon the Bt traits planted in your fields. Please refer to your seed technology use guide(s)/stewardship agreement(s) for specific refuge configuration options and compliance requirements.

  • Block refuge (adjacent) – A block of non-Bt corn immediately adjacent to or separated only by a road or ditch from the Bt corn field that satisfies the full field refuge requirements for the particular Bt trait
  • Block refuge (within) – A block of non-Bt corn within the Bt corn field that satisfies the full field refuge requirements for the particular Bt trait
  • Refuge perimeter – Non-Bt corn surrounding the Bt corn within the field
  • Split planter refuge – Strips of non-Bt corn at least four rows wide with the Bt corn field (6 rows preferred)
  • Pivot corners refuge – Non-Bt corn in pivot corners within the Bt corn field
  • Separate field refuge – A separate field of non-Bt corn within ½ mile of the Bt corn field (1/4 mile preferred)
  • Adjacent field refuge – A separate field of non-Bt corn either immediately adjacent to or separated only by a road or ditch (not another field) from the Bt corn field
  • Refuge-in-a-bag –Bt-traited seeds and non-Bt seeds are combined in each seed order and dispersed throughout the field when planting

Refuge-in-a-Bag

When Bt hybrids first became available, structured refuge was required throughout all corn-growing regions, meaning that defined areas of refuge, such as blocks or planter strips, were the norm. Refuge-in-a-bag, often referred to as integrated refuge, was introduced to the Corn Belt in 2010 to make insect resistance management compliance easier for farmers to navigate. Integrated refuge is the common refuge-planting strategy across the Midwest today and meets all current refuge-planting requirements.

Refuge Management

In order to maximize the effectiveness of the refuge, non-Bt corn and Bt corn should be managed in a similar manner. This can be accomplished by planting non-Bt corn at the same time or close to the same time as Bt corn. In addition, select non-Bt hybrids that have similar growth and development characteristics.

More Information

To make refuge planting decisions easier for your farm, use this free Insect Resistance Management Calculator: www.IRMCalculator.com

Additional reference materials are available on the following websites:

www.traitstewardship.com

www.monsanto.com/products/product-stewardship

www.pioneer.com/stewardship

www.syngentastewardship.com