Revolutionizing weed science by understanding plants' ability to eavesdrop on the competition


Plants communicate. So much so, that they actually sense weed competition and reduce yield potential even before they emerge from the ground.

It may sound like science fiction, but it’s just one of the many scientific facts that University of Guelph weed scientist Dr. Clarence Swanton has helped prove during his 35-year career. Over the years, Swanton’s work on weed competition has yielded revolutionary agronomic and production strategies to significantly increase yields, especially for corn and soybeans.

Clarence Swanton’s work clearly established that when it comes to weed management, timing is everything.

Speaking this week at the Canadian Weed Science Society (CWSS) annual meeting in Niagara Falls, Ontario, Swanton shared how coming to understand a plant’s ability to sense competition played a critical role in modern weed control strategies. Essentially, Swanton helped usher in the thinking that weeds that emerge with or shortly after the crop cause irreversible yield loss. It was Swanton that defined the critical weed-free period as the 1st to 3rd trifoliate (V2-V3) for soybeans and 3 to 8-leaf in corn.

Swanton’s work clearly established that when it comes to weed management, timing is everything. He notes that yield loss varies with crop leaf stage, but in general, the later weeds are controlled, the greater the impact. Yield loss attributed to weed competition is also highly measurable, he notes. It can be calculated by the day, it’s rapid and irreversible.

In this interview with RealAgiculture’s Bernard Tobin, Swanton discusses the “physiology of fear” and how plants sense weed pressure and respond by reducing size and yield. He also makes reference to a famous Christmas film when referring to the “ghost of competition past” to explain that weed pressure experienced early in a plant’s life affects it throughout its entire life cycle and will impact the final yield.  Story continues after the interview.

All this understanding of how plants communicate inspired a question from the CWSS audience on whether weed scientists might somehow be able to jam the weed communication signals to enhance plant growth. Swanton says that’s really the story of modern seed treatments, which are “very beneficial in helping a plant reduce the impact of that communication between a plant and a weed.”

And there’s still more to learn from weed whispering.

Swanton is also excited about gaining a greater understanding of how the presence of weeds could impact the uptake of nitrogen by soybean plants. “Now, we’re looking at a soybean plant prior to nodulation, and to our surprise we found that it might be possible that the presence of a weed changes the ability of a soybean plant to mobilize nitrogen. It’s never been seen or heard of in the biological world before.”

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