Insecticide resistance, while not currently as prevalent in the United States as herbicide resistance, should concern soybean farmers. As new insecticide technology development slows, it is important to prevent the development of resistance to preserve the current tools and technologies for farmers in the future.
Integrated pest management (IPM) strategies play an important role in insect resistance management. These management practices combine cultural and chemical approaches with the intention of diversifying the practices used to control insect pests and reduce insect pest exposure to chemical control. Although chemical control is a valuable strategy for managing insects, farmers should implement cultural and other nonchemical control methods to avoid the risk of developing insect resistance.
Implement cultural practices before relying on chemical control. Crop rotation, scouting and identifying insects and following economic thresholds for present insects are all examples of cultural practices. Cultural practices diversify insect management practices, and often can eliminate pests without the use of insecticides.
Scouting and Identification
Scouting for infestation and damage levels from insects help farmers properly identify insects and determine the appropriate insecticide and timing for application. Proper identification allows farmers to choose the most effective insecticides and management strategies to target the pest. Farmers should scout throughout the season to follow the development of insect populations and continue to monitor the crop after application to assess the effectiveness of control.
Economic thresholds indicate when the yield saved by making an application outweighs the cost of the application. Follow the established thresholds for common insect pests to determine when to apply insecticides. Scout for levels of infestation and damage to determine when the threshold has been met and choose the most effective insecticide.
Certain classes of insecticides are better are targeting certain insect pests. This is referred to as product efficacy. To maximize product efficacy, the proper formulations and methods must be used. Before application, consult recommendations for your area and read the product label to be certain of application parameters.
To preserve product efficacy, rotate multiple insecticide modes of action throughout each growing season to reduce the opportunity for resistance development. This preserves these modes of action by ensuring that the same generation of insect is not exposed to the same insecticide(s). Insects that survived the initial application can be removed with a follow-up application using a different mode of action.
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
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.
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.
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: