Gardeners Creating Poisonous 'Superweed,' Scientists Warn

Mowing a weed just makes it stronger, according to a study published in Nature's Scientific Reports, and the consequences can be severe for the agricultural industry.

The mowing of Solanum elaeagnifolium strengthens its defenses, potentially creating a "superweed."

The weed, also known as silverleaf nightshade, poses a significant threat to agriculture by absorbing nutrients intended for cash crops. It is identifiable by its purple, sometimes white or light, flowers, prickly spines, and poisonous berries, and can be found from south Texas to South Africa and Greece.

Rupesh Kariyat, an associate professor of entomology and plant pathology with the Arkansas Agricultural Experiment Station, has dedicated over 10 years to studying silverleaf nightshade and his research began at the University of Texas Rio Grande Valley and spanned five years.

Kariyat and his graduate student, Alejandro Vasquez, observed the effects of mowing on the weed. Since joining the University of Arkansas System Division of Agriculture in 2022, Kariyat has continued this work.

The study's findings revealed that mowing silverleaf nightshade does not merely suppress the plant, but instead triggers several defensive adaptations.

The study involved monitoring fields of mowed, unmowed, and frequently mowed silverleaf nightshade around Edinburg, Texas. The team discovered that mowed plants developed deeper taproots, sometimes reaching nearly five feet deep.

This adaptation allows the plant to access water and nutrients more efficiently. Additionally, mowed plants produced more spines on their stems, a mechanical defense against caterpillars and other herbivores. The flowers of mowed plants also became more toxic, reducing herbivore pressure and enhancing the plant's survival and reproductive success.

Interestingly, the frequency of mowing played a critical role in these adaptations. Plants subjected to more frequent cutting exhibited even greater defensive traits, including larger and heavier flowers. The increased reproductive and defensive mechanisms suggest that silverleaf can adapt quickly to human-induced disturbances.

"You are trying to mow these plants so that the plants are getting eliminated," Kariyat said in a statement. "But what you are actually doing here, you are making them much worse, much stronger."

It poses a significant threat to agriculture by absorbing nutrients intended for cash crops. The weed belongs to the solanaceae family, which also includes crops like tomatoes, potatoes, peppers, and eggplants, along with other toxic relatives such as black nightshade and Carolina horsenettle.

This finding raises significant questions about current weed management practices, especially for a plant that infests fields and competes with crops across various regions globally.

These insights into the defensive capabilities of silverleaf when reacting to mowing could prompt further research into alternative weed management strategies. Understanding the plant's adaptive mechanisms is crucial for developing more effective and sustainable control methods.

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