Traited Corn Hybrids – Is There Risk of Unintended Pest Consequences?

David J. Isenhour, PhD

David holds a Ph.D of Entomology from University of Kentucky. He has over twenty-five years of experience in the seed industry and has headed a research and development team that had responsibilities for covering 16 countries worldwide

The economic and environmental benefits of traited hybrids, also referred to as “GMO corn” have been significant. In my opinion, those benefits have not been fully assessed or appreciated in the non-agricultural community. Not only can traited hybrids bring us greater yields to satisfy the demands of the world population, they also don’t need as many insecticides due to their natural resistance, which reduces environmental impact. But does the amazing success in creating insect-resistant corn hybrids mean we can completely stop using insecticides to protect corn going forward? It might surprise you that the answer is “no.”

Current Insect Resistance

Traited corn hybrids have been extremely effective in defending against attack by the insects they’ve been bred to resist. These hybrids protect against many above ground pests, such as the European corn borer, southwestern corn borer, corn earworm, western bean cutworm, fall armyworm and even to some extent black cutworms. But below ground, traited hybrids are only resistant to corn rootworm larvae. This singular protection could have unintended consequences if other below ground pests are not accounted for. Further, even the protection offered against corn rootworms is not perfect. The current second generation of stacked traited hybrids have shown significantly greater protection than the first generation, but damage still occurs.

Risks and Possible Consequences

Because of traited corn’s ability to resist corn rootworm, many new planters on the market no longer come with “boxes” to enable at-planting application of granular insecticides. And many farmers have removed these boxes from their existing planters. The problem with this is that traited corn hybrids are not resistant against two other common below-ground pests, grubs and wireworms. Those same soil insecticides which controlled rootworm also provided protection against grubs and wireworms, protection which is now gone.

A grower might think the risk for grubs and wireworms is  limited to continuous corn fields, and that a rotation system will get rid of non-corn rootworm pests. This might not be a safe assumption. Some species of grubs and wireworms have unique live cycles, in which they require more than a single year to complete their development. Rotation alone might not prevent them from inflicting damage to a corn crop. Other risks include soil types and field topography. Each grower will need to access their fields and develop specific practices for hybrid selection, protection practices and subsequent in-field monitoring.

This is not a shout of the “sky is falling” with respect to grubs and wireworms, but it is a warning that those pest complexes pose risks we need to be aware of and monitor. “Plant it and forget it” is never an option when it comes to insects.

In all situations when using crop protection products such as insecticides – read the label, follow the label, and use all recommended personal protection equipment. Always be safe.

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