Soybean School: Managing weedy fields after crop emergence

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When it comes to weed control in soybeans, it’s always best to start clean and stay clean. But when fieldwork and planting are delayed thanks to poor spring conditions, growers are often forced to plant now and spray later.

That’s the situation many Ontario growers have experienced in 2024 as wet spring conditions dictated that many soybean fields were planted without an opportunity to apply pre-emergent residual herbicides. The compacted spring means sprayers are racing to cover corn acres and apply wheat fungicides while many soybean fields that haven’t been sprayed have been quickly overrun by weeds.

On this episode of RealAgriculture Soybean School, BASF Canada agronomist Rob Miller shares strategies and options for growers in this pinch.

“In an IP soybean situation, your options are somewhat limited because you always want to get that residual down to carry you through to that canopy closure,” says Miller. In this case, growers can’t use some soil-applied products like metribuzin, but a residual product will still play a key role in helping control resistant weeds like Canada fleabane, Group 2 and Group 5-resistant lambquarters, waterhemp and Group 14-resistant ragweed. Miller advises growers to check product labels to ensure products can be applied post emergence.

The next concern is broadleaf weeds. Miller says they’re always tougher to control and they can have a serious impact on yield, especially in IP soybeans. The final concern is grasses like foxtail, barnyard grass and crabgrass.

When it comes to post-emergence strategy, Miller says growers need to be aware of antagonism when tank mixing products. In some case, splitting applications may be the best choice, and a five to seven-day interval may be advisable depending on the mix.

In the video, Miller also discusses the importance of selecting the right adjuvant for product application, and to be aware of products that may already contain adjuvant. Watch the video below.

Tap here for more Soybean School videos.

 

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