Mowing your yard too often may create unstoppable 'superweeds'

We all love a neatly manicured lawn. But what if frequently mowing the yard in our quest for tidiness is inadvertently creating a legion of superweeds? 

A recent study on the seemingly innocuous silverleaf nightshade (Solanum elaeagnifolium) has revealed a startling truth.

This unassuming weed, along with dandelions and many others, is a master of adaptation, evolving into a tougher, more resilient version of itself when faced with frequent mowing.

Why superweeds like mowing

Superweeds are wild plants that develop resistance to herbicides. This resistance often results from the repeated use of the same herbicide, like glyphosate, on crops.

As a consequence, these weeds can survive treatments meant to eliminate them, making them harder to control.

Genetically modified (GM) crops, designed to withstand herbicides, inadvertently contribute to the rise of superweeds. When these herbicides kill off non-resistant weeds, resistant ones thrive and spread.

Superweeds pose a significant threat to agriculture. They compete with crops for resources, leading to lower yields and higher costs for farmers.

Controlling these weeds often requires stronger, more expensive herbicides or alternative management strategies, which can further harm the environment.

As superweeds continue to evolve, sustainable weed management practices and diversified farming techniques become crucial in mitigating their impact.

Unassuming purple weed spreading rapidly

Silverleaf nightshade may not be a household name, but this pervasive weed is found from the sun-soaked fields of south Texas to the ancient landscapes of South Africa and Greece. 

With its delicate purple flowers (sometimes white or light purple), prickly spines, and toxic berries, it’s not a plant you want to mess with. 

Interestingly, it shares a family tree with some of our favorite crops, including tomatoes, potatoes, peppers, and eggplants.

Rupesh Kariyat, an associate professor of entomology and plant pathology, has been studying this unassuming weed for over a decade. 

His research, which began at the University of Texas Rio Grande Valley, has revealed some fascinating insights into the plant’s response to frequent mowing.

Mowing launches “survival of the fittest” contest

Kariyat’s research has found that frequent mowing doesn’t just trim the silverleaf nightshade; it triggers a series of remarkable defense mechanisms. 

“You are trying to mow these plants so that the plants are getting eliminated,” Kariyat explains, “But what you are actually doing here, you are making them much worse, much stronger.”

Under the pressure of frequent mowing, the plant’s taproot burrows deeper into the soil, reaching depths of nearly 5 feet to access water and nutrients. 

More spikes sprout on its stem to deter hungry caterpillars, and the flowers themselves become more toxic, reducing the threat from natural predators.

The plant even employs a clever strategy for seed germination, producing some that sprout quickly and others that lie dormant, like time bombs. 

This “staggered” germination ensures the plant’s survival over the long haul, even in the face of repeated mowing.

Superweeds spawn from mowing ripple effect

While Kariyat’s research focused specifically on silverleaf nightshade, its findings have far-reaching implications. 

Other weeds, even close relatives of the nightshade, may react similarly to frequent mowing, potentially creating a whole army of superweeds.

“This should be something that we consider when we make management plans,” Kariyat warns. “Management practices need to be better understood using the ecology and biology of the species and the other species which interact with them.”

Adaptation of silverleaf nightshade

The silverleaf nightshade’s response to mowing is a fascinating example of adaptation in action. It demonstrates the incredible resilience of nature and the unintended consequences of human intervention.

The plant’s ability to evolve in response to environmental pressures is a testament to its tenacity and adaptability. It’s a reminder that even the most unassuming organisms can possess remarkable survival skills.

Mowing superweeds requires caution

So, what does this mean for our manicured lawns? Should we abandon our mowers altogether? Not necessarily. 

Kariyat’s research does suggest that we should approach mowing with a bit more caution and consider alternative weed management strategies.

For instance, tilling areas infested with silverleaf nightshade can actually worsen the problem by spreading the plant‘s rhizomic roots, which can propagate asexually.

“As scientists, we want our research to be accessible and applicable to anyone, and mowing is a concept the world at large can understand,” says Alejandro Vasquez, the lead author of the study and a Ph.D. student at the University of Arkansas.

So, from now when you fire up your mower, spare a thought for the unassuming superweeds lurking in your lawn. They may be small, but they’re far more resilient than you think.

The study is published in the journal Scientific Reports.

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