Tackling Corn Rootworm Resistance

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By Adam Parker, Territory Manager at Maizex Seeds

Background

There have been multiple cases of confirmed Corn Rootworm (CRW) resistance to rootworm-traited corn hybrids in Ontario, resulting primarily from where corn-on-corn has been the principle crop rotation. This is a concern as the viability of CRW traits are in question. Additionally, there are no new traits or traits that vary significantly from curren technologies on the horizon.

Corn has become an essential crop for livestock production. Corn is now the main feed ingredient for all major livestock species including dairy, beef, swine and poultry in most areas of Eastern Canada. With livestock comes manure, and corn is one of the few crops that can excel in high-fertility scenarios without the negative effects from lodging, diseases, etc. that are often associated with alternative rotation crops.

Because of this, some of our livestock systems have become too dependent on multiple years of corn-on-corn or, in some cases, continuous corn on their land base. The challenge and goal now become to preserve our effective rootworm traits and overall crop yield while continuing to reliably produce feed for our livestock. The result has been an industry call to action to take effective steps to manage resistance development to meet this goal. If nothing is done to reduce the risk of resistance development, key traits will become ineffective in areas of overreliance. Producers will be faced with inevitable CRW damage in corn fields, with reduced yields, goose-necked corn, and increased lodging.

Rotations

There are strategies for managing CRW resistance. The simplest management strategy is to not grow corn on corn. Planting other crops that are not corn greatly reduces the populations of CRW. In doing so, we can use corn hybrids in subsequent years that do not have the CRW traits, which is key to managing and reducing resistant populations. Although this may sound simple, some producers who have constrained land bases and a need to maximize their feed production will not be able to simply grow a different crop.

In these cases, swapping acres with neighbouring farm operations for a year to break the corn-on-corn cycle would be advantageous. This may also be an effective way to help spread your manure to new fields for nutrient management reasons while still effectively using it for your corn crop. The challenge becomes that, the further the fields are away from the barn, silage pit, or manure pit, the further the grower will have to haul the feed and manure. Taking the effort to haul feed and manure a longer distance to rotated fields is best for a long-term stewardship solution for CRW resistance. With modern, large, fast equipment, traveling a few farms further down the road is more practical than it used to be.

OMAFRA has suggested that producers consider utilizing other feed crops to become less dependent on corn for grain and silage. Examples would be using cereal rye and sorghum to replace corn silage and to use wheat and barley to replace grain corn in other diets. This may not be a practical solution on any scale, given in particular reduced income when comparing feed efficiency and utilization of other feed crops compared to corn.

Insecticides

Other management strategies that are available to producers to manage CRW involve using insecticides either as high-rate neonicotinoid seed treatments or as alternative in-furrow applications to protect corn plants. These options bring additional costs to the producer but offer a significant return on investment when compared to not having any protection for CRW in a corn-on-corn situation. It should be remembered that history tells us seed treatments are effective but not at the same level as what we have experienced with in-hybrid traits. However, this is better than relying on traits exclusively with a high risk of resistance development.

In-furrow insecticide applications are not a new technology; they can be effective, but they are less available today. Very few planters have insecticide application systems on-board. The industry is now working with crop-protection companies to review what options can be made available to Ontario farmers in high-risk CRW situations. If in-furrow insecticides will be needed as part of a management strategy, today it will require investment in closed-loop application systems similar to what is being used in some regions of the United States. These systems dramatically reduce grower exposure to the insecticide.

Strategies

With all of these issues and solutions in mind, there is no simple or easy answer to the problem of CRW resistance. Given the economics and benefits to feeding corn, livestock operations will continue to look to corn as a primary feed source. The most practical solution is to use a rotation on your farms if at all possible.

Resistance management for corn rootworm needs to move to a front-of-mind issue, especially for some growers. OMAFRA and the Corn Pest Coalition have made some recommendations to lessen the exposure of CRW traits. These include:

  • In first-year corn on rotated ground, use hybrids that do not include a CRW trait.
  • In second-year corn, use non-CRW hybrids, scout for CRW adults in the prior year, and use insecticides for additional root protection.
  • In third-year corn, use pyramid CRW-traited hybrids.
  • Do not use insecticides on CRW-traited hybrids, as the combination can increase the risk of rootworm resistance.

The idea of not using CRW-traited hybrids for second-year corn goes against previous agronomic recommendations. However, it is apparent that some new approaches, certainly in high-risk areas, are inevitable. Figure 1 demonstrates the decreased exposure of CRW traits by including some additional rotation, scouting, insecticide use, and more selective use of CRW-traited hybrids compared with a system that is still dominated by corn but where CRW-traited hybrids are the only tool for protecting the corn crop from CRW damage.

There will be a number of presentations and industry discussions on this topic this winter. As you plan your 2021 crop rotation, talk with your local agronomist for recommendations specific for your farm.