Soybean School: How Dry is Too Dry for Residual Weed Control?


Dry conditions can be tough on soybean residual herbicides, but with a little rain, they’re up to the task, says BASF field biologist Rob Miller.

He concedes that in a dry year like 2016 in Ontario, residuals can be less effective, “but you’re still seeing the value of residual weed control, especially with burndown. Even with the dry conditions this spring you’re still looking at looking at 80% weed control.”

In this episode of the Soybean School, Miller takes a close look at test plots at BASF’s Maryhill, Ontario research farm and shares insights gleaned from this year’s dry, stressful growing conditions.

Miller notes that this year weeds tended to germinate at lower depths — anywhere from two to three inches deep — making them very difficult to control.

“One of the things you have to consider in a dry year is coming in a little earlier than planned to do that in-crop herbicide application … some of the weeds might escape or get a little too large if you wait too long.”

Overall, residual herbicide activation depends on a number of environmental conditions, including soil type, but moisture certainly plays a key role. Different herbicides require varying amounts of rainfall for activation.

“For those that require less, you’re looking at a minimum quarter inch for activation, but in general, half an inch is better for consistent weed control,” says Miller. He notes that some products require three-quarters of an inch for activation and consistent control.

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Soybean School (view all)Season 5 (2016) Episode 16

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