Weedy conversations

A new inexpensive tool has emerged in the fight against weed resistance

In a newly released study, scientists at the University of Illinois and USDA’s Agricultural Research Service offer a new tool to fight herbicide resistant weeds that is not only highly effective, it’s free.

All it costs is a conversation.

Waterhemp, a weedy nemesis of corn and soybean farmers, has developed resistance to multiple herbicide modes of action, often in the same plant. Even farmers using the latest recommendations for tank mixtures are fighting an uphill battle, with long-distance movement of pollen and seeds bringing the potential for new types of resistance into their fields each year.

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“This tool is free, but it requires that people talk to each other and work together as opposed to doing everything on their own,” said Adam Davis, research ecologist with USDA-ARS and adjunct professor in the Department of Crop Sciences at U of I in a release.

The tool is co-operative weed management — in other words, making decisions about how to manage herbicide-resistant weeds in co-operation with neighbouring farms. The more farms working together, and the larger area covered, the better.

Davis and his team used a computer simulation of waterhemp resistance evolution through time and space. They ran the simulation using real numbers and management practices from the past, starting in 1987, to arrive at a realistic representation of herbicide resistance in waterhemp in 2015. Then they forecast 35 years into the future to determine how resistance might change under different management and co-operative scenarios.

“The crux of the story is that if you do good stuff and you aggregate it at larger spatial scales, it gets even better. If you do bad stuff and you aggregate it at large spatial scales, it gets even worse,” Davis says.

The “bad stuff,” according to the simulation, is using a single herbicide mode of action year after year.

If farmers invested in tank mixtures of herbicides representing three or four modes of action, the evolution and spread of resistance was delayed, and the delay got longer with increasing levels of co-operation.

Davis said the specific number of farms making collective weed management decisions isn’t as important as the spatial scale they cover. He suggests forming weed management areas at the township scale and above.

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