MANAGING INSECT RESISTANCE THROUGH REFUGE PLANTING

Refuge planting is a mandatory best management practice for Bt corn growers. If you have integrated refuge (the bag contains Bt seed mixed with non-Bt seed) it is already part of your field. If you plant Bt without refuge mixed in the bag, you will need to construct a refuge in your field. This factsheet tells you how to do it.

WHAT IS A REFUGE?

A refuge is a portion of the crop that does not contain the Bt trait. The refuge provides a habitat for target insects to feed, mate and reproduce without being exposed to the Bt trait, allowing them to maintain their susceptibility. The goal of the refuge is to ensure that resistance genes remain rare in the target pest population, being diluted by the more abundant susceptible insects and delaying the onset of resistance.

HOW TO PLANT A REFUGE

Most products today have automatic 100 percent refuge compliance. These products have at least two modes of action (MOAs) per target pest, which allows for a reduced amount of non-Bt refuge seed to be mixed right into the bag. Refer to the Bt Corn 101 factsheet for more info on MOAs.

Single-MOA products, with only one trait active against a given target pest, require planting 20 percent structured refuge. Use this Canadian Corn Refuge Hybrid Selector to find out how much refuge you need to plant with your Bt corn hybrid and what refuge hybrids are available in your area.

You must follow the refuge requirements specific to the type of insect resistant corn you plant. The size and location of the refuge required varies depending on which trait is used and which insect is being controlled. (See below for rationale of different refuge requirements depending on target pest.)

Thanks to the high adoption of planting integrated refuge products, overall grower compliance with the refuge requirement is very high (95%).

It remains important to continue to plant refuge for products that do not have a refuge built into the seed bag. This practice is low among growers planting products that do not have integrated refuge (35%).

GUIDELINES FOR PLANTING STRUCTURED REFUGE

Where do I plant the refuge?

  • European corn borer (ECB) transgenic hybrids: refuge must be within 400 metres
  • Corn rootworm (CRW) or ECB + CRW transgenic hybrids: refuge must be planted within the field or in an adjacent field with the same crop rotation history

You can find refuge planting configurations for specific Bt hybrids at cornpest.ca.

WHY DO REFUGE REQUIREMENTS VARY BETWEEN Bt HYBRIDS?

Refuge requirements for CRW versus ECB Bt hybrids are different because of the pests’ biological differences. ECB and CRW vary in their exposure to selection pressure exerted by Bt proteins. Bt traits targeting ECB express a high dose of protein against this pest with the intent to kill all ECB larvae with no genes for resistance, plus those with one copy of a resistance gene. Although CRW Bt corn hybrids are effective at protecting the roots from larval injury, adult emergence can sometimes occur. CRW also tend to mate in the same field as they emerge, reducing the amount of genetic mixing from nearby non-Bt refuge fields. As a result, the CRW refuge must be placed within or adjacent to the CRW or stack field to accommodate the limited movement of CRW adults at mating.

 

Refuge requirements for CRW versus ECB Bt hybrids are different because of the pests’ biological differences.

 

What hybrids can I use as refuge?

  • Conventional or herbicide-tolerant corn hybrids can be used if they are of similar maturity and agronomics as the transgenic corn hybrid (within 100-150 CHU).
  • The refuge must be planted at the same time as the transgenic corn.
  • Mixing transgenic and non-transgenic corn seed on-farm is not permitted.

Can I use insecticides in the refuge?

  • The refuge may be treated for CRW larval control with soil-applied or seed insecticides if economic thresholds prescribe it.
  • If pest injury from other target caterpillar pests (e.g., western bean cutworm) exceed the economic threshold, a foliar insecticide for control of caterpillar pests can be applied to both the Bt and non-Bt corn in the field.
  • Sprayable Bt insecticides (or foliar sprays containing a Bt) must not be applied to the refuge corn.

Although awareness of the requirement to keep accurate records of where Bt hybrids are planted is low (60%), compliance is not an issue (90%). This indicates that in practice record keeping is done by almost all growers, however, fewer growers knew it was an IRM requirement.

1 Bt Corn Insect Resistance Management Study, iFusion Research, August/September 2019

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This information is brought to you by CropLife Canada and the Canadian Corn Pest Coalition.