Rootworms Resistant to Bt Gain Ground
“However, there is some evidence building that there may be some cross resistance between it and the Cry3Bb1.”
Dirk Benson, technology manager, Syngenta, cautioned against jumping to conclusions of resistance when it comes to “unexpected damage.” Although the industry and the EPA agreed to the validity of a number of protocols for evaluating resistance, none when used alone are definitive in determining resistance. Benson argued those conditions are radically different from field situations and can depend on the quality of the insect sample taken. He further pointed out the multitude of conditions that can affect Bt efficacy, including synchrony of planting date, larval emergence, root radical development and population pressure. All can affect whether the CRW feed on smaller early root mass or later larger root mass that is better able to support the plant. With all the variables growers face, he challenged them to practice integrated pest management, of which insect resistance management is a component.
“Rotating traits is one thing, but growers need to consider rotating crops as well,” he said. “We need to break the biological cycle of the insect, or we are just running an experiment around resistance development. We all know what the answer will be. Just look at multiple applications of glyphosate without breaking the cycle. Growers need to look long term.”
NEW ANSWERS NEEDED
Benson noted that Syngenta appreciates the need for multiple modes of action and new answers to the CRW problem. “We have an active discovery engine in both chemical and seed traits,” he said. “Soil-applied insecticides certainly have their place. Seeds, chemistry and traits all have a role.”
Rich Porter, Amvac, noted that continuous corn growers in many areas are experiencing CRW pressure not seen in years.
“In many situations the pressure has become overwhelming,” he said. “Soil insecticides have challenges, and now areas are seeing traits with quite a few challenges. We are emphasizing to retailers that CRW management will take more diligence and more scouting. They can no longer assume a single technology will meet grower expectations for corn rootworm management, but need to consider multiple strategies to control this difficult pest.”
Having purchased or licensed the bulk of the granular soil insecticides on the market during the rise of CRW Bt traitbased control, including Aztec, Counter and SmartChoice, the company has been preparing for the current situation.
Porter said Amvac has been looking at newer technologies and working with university researchers since 2007, combining granular soil insecticides with traits.
“Where there has been significant rootworm damage, if you have an overlay or second mode of action, there is a significant reduction in feeding damage a high percentage of the time,” explained Porter. “CRW is a very humbling pest. There is no single bullet, no single technology. The trait technology that came on 10 years ago has not been the end solution in continuous corn or, it appears, even in first-year corn.”
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