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Impact of Climate Change on Herbicide Effectiveness
Recent research has illuminated an alarming trend regarding the effectiveness of herbicides in agriculture, particularly amidst our changing climate. A collaborative study led by the USDA Agricultural Research Service and the University of Illinois Urbana-Champaign has demonstrated that not only soil-applied herbicides but also post-emergence (POST) herbicides are less effective against common agricultural weeds.
Utilizing a comprehensive 30-year dataset from 16 Extension weed science programs across the U.S. Corn Belt, researchers observed that variable weather significantly hampered the efficacy of three major POST herbicides—fomesafen, glyphosate, and mesotrione—on prevalent weeds threatening corn and soybean crops. This decreased efficacy raises concerns regarding crop yields and, by extension, global food security if adequate weed control cannot be maintained.
“Weather plays a crucial role not just immediately after the application of POST herbicides,” stated Chris Landau, the postdoctoral researcher at USDA-ARS and the study’s lead author. “Our findings indicate that both air temperature and precipitation impact herbicide efficacy well before and after application. The volume of data we analyzed allowed us to explore weather effects on POST herbicide effectiveness across diverse environments, surpassing earlier examinations.”
Particularly, the research revealed that average air temperatures falling below 66 or exceeding 77 degrees Fahrenheit diminished the effectiveness of the herbicides on weeds such as waterhemp, giant foxtail, and morning-glory. While the historical dataset did not clarify the underlying reasons behind this diminished efficacy, existing literature offers some insights.
“Warmer temperatures before application can accelerate weed growth, resulting in larger plants—making them more resilient to herbicidal interventions,” explained co-author Marty Williams, an ecologist with USDA-ARS and an affiliate professor at the University of Illinois. “Conversely, high temperatures in the aftermath of application could enhance plant metabolism, thus neutralizing the herbicides more quickly and reducing their effectiveness.”
On the flip side, lower temperatures tend to impede the metabolism and distribution of herbicides within the plants, thereby also diminishing their effect.
The analysis highlights that temperature isn’t the sole factor to consider; precipitation patterns also play a critical role. For instance, dry conditions in the 10 days preceding herbicide application or excessive moisture within 10 days after can alter how effective the treatment will be.
Landau refers to preceding research to illustrate why moisture extremes might lead to decreased herbicidal effectiveness. Drought conditions can trigger plants to thicken their waxy cuticles, which, while beneficial for water preservation, hinder the absorption of foliar-applied herbicides. Conversely, significant rainfall may wash away herbicides shortly after application or initiate stress responses that slow plant growth and impede the movement of herbicides to the areas needing treatment within the plants.
The interplay of these factors poses additional challenges for farmers already grappling with the repercussions of climate change, such as flooding in spring and droughts during summer. “The tools utilized for weed management are intricately linked to these shifting weather patterns, making farming increasingly challenging,” Williams noted.
Although the study primarily focused on individual herbicides, the researchers also assessed the efficacy of combining glyphosate and fomesafen. Their findings suggest that this combination offers improved weed control in variable weather conditions. However, the team cautioned that relying solely on POST combinations may not provide complete protection against weed proliferation. They emphasized the importance of integrating effective soil-applied residual herbicides and non-chemical control methods for more reliable weed management.
Williams argues that the discipline of weed science must evolve to address these ongoing challenges. “Weeds are adapting at a pace that outstrips our current management practices. Climate change is likely to accelerate this evolution,” he stated. “It is essential to proactively innovate in research and development to avoid the severe consequences of failing weed control.”
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