Don’t Let Early-season Weeds Bully Your Soybeans

May 30, 2019

By Allan Froese, Product Selection Lead, Soybeans, Western Canada, Syngenta

Start clean and stay clean. It’s a simple weed control message, but when it comes to soybean yield it really does speak volumes.

Research conducted by Dr. Clarence Swanton from the University of Guelph shows that early weed pressure can have a significant impact on soybean yield — the plant can actually sense weeds growing on the soil surface before it emerges and, as a result, will start to change its physiology. When the plant detects weeds during the early growing stage — from the 1st to 3rd trifoliate (V1 to V3) — it starts to reduce yield potential based on the competition from the surrounding weeds.

We generally refer to this phase as the critical weed-free period. Depending on the amount of weed pressure, growers could lose from 0.5 to 2 bushels/acre per day when weeds are not controlled.

Row spacing can make a difference

There are a number of cultural and herbicide management strategies that can help keep your soybean fields clean during the early season. University of Manitoba research scientist Dr. Rob Gulden and M.Sc. student Jon Rosset recently studied ways to actually reduce or shorten the critical weed-free period. Basically, they were looking to reduce that time period when weed pressure is altering the plant and stealing your yield potential. Their research indicated that narrowing row spacing, maintaining adequate soybean plant densities and variety choice all affected the end of the critical weed-free period to varying degrees.

Of the three cultural practices, Gulden and Rosset reported that reducing soybean row spacing had the greatest impact on shortening the weed-free period and required fewer in-crop herbicide applications. The research shows that it simply takes a longer time for wider rows to close and the extra sunlight gives weeds a better chance to compete.

From a plant density perspective, they concluded that target densities below 180,000 plants/acre may lead to additional in-crop herbicide requirements. When it comes to variety selection, the researchers noted that growing a variety that has demonstrated competitive growth in local growing conditions is a good strategy.

Incorporating residual herbicides

Seed and herbicide technology also play a key role in helping growers start clean and stay clean throughout the critical weed-free period. A good way to do this is to start with a pre-emergence burndown that includes a residual herbicide. There are several good options that can be used, depending on your weed spectrum. If you choose to skip this option and opt for a post-emerge program, the herbicide should be applied early enough for the weeds to be dead by V1. The issue with this plan is that, ideally, your soybean crop doesn’t see weeds until it’s past the V3 stage to maximize yield potential.

Remember, under good growing conditions, a new trifoliate emerges approximately every five to seven days, so you’re counting on your post-emerge application to keep the field clean for up to a month. This will most likely require a second post-emerge application within that timeframe.

Roundup Ready 2 Xtend and dicamba

A relatively new tool available to growers is Roundup Ready 2 Xtend® soybeans, which allow you to add another mode of action into your weed control plan and gain a tremendous management advantage. Roundup Ready 2 Xtend® soybeans give you the opportunity to incorporate approved dicamba formulations at either a pre-emerge or early in-crop application timing. This provides additional herbicide tolerance to help control resistant and other tough-to-control weeds.

For example, Tavium™ Plus VaporGrip® Technology herbicide – which is applied at the pre-emerge stage - provides powerful, broad-spectrum control, including the ability to control glyphosate-resistant weeds with dicamba. The pre-mix formulation also offers residual grass control with the addition of Dual II Magnum®.

Combining cultural management decisions and technology to control weeds before soybean seedlings sense competition is a winning strategy. It really does help create a confident soybean crop that has higher yield potential in the absence of those early-season weeds that bully seedlings and steal yield.

Monsanto Company is a member of Excellence Through Stewardship® (ETS). Monsanto products are commercialized in accordance with ETS Product Launch Stewardship Guidance, and in compliance with Monsanto’s Policy for Commercialization of Biotechnology-Derived Plant Products in Commodity Crops. This product has been approved for import into key export markets with functioning regulatory systems. Any crop or material produced from this product can only be exported to, or used, processed or sold in countries where all necessary regulatory approvals have been granted. It is a violation of national and international law to move material containing biotech traits across boundaries into nations where import is not permitted. Growers should talk to their grain handler or product purchaser to confirm their buying position for this product. Excellence Through Stewardship® is a registered trademark of Excellence Through Stewardship.

Always read and follow label directions. Tavium™, the Alliance Frame, the Purpose Icon and the Syngenta logo are trademarks of a Syngenta Group Company. Other trademarks are the property of their respective owners. Genuity® Roundup Ready 2 Yield® crops contain genes that confer tolerance to glyphosate, the active ingredient in Roundup® brand agricultural herbicides. Roundup Ready 2 Xtend® soybeans contain genes that confer tolerance to glyphosate, an active ingredient in Roundup® brand agricultural herbicides, and dicamba, the active ingredient in XtendiMax™ herbicide with VaporGrip™ Technology. Agricultural herbicides containing glyphosate will kill crops that are not tolerant to glyphosate, and those containing dicamba will kill crops that are not tolerant to dicamba. Genuity®, Genuity and Design®, Roundup Ready 2 Xtend®, Roundup Ready 2 Yield®, Roundup®, VaporGrip™ and XtendiMax™ are trademarks of Monsanto Technology LLC, Monsanto Canada, Inc. licensee. © 2018 Monsanto Canada Inc. VaporGrip® is a registered trademark of, and used under license from, Monsanto Technology LLC. © 2019 Syngenta.

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