Study: The effectiveness of glyphosate over time and sustainable weed control strategies

2024-01-22 07:49:07

Study: The effectiveness of glyphosate over time and sustainable weed control strategies

AGDAILY Reporters*

Image : stockstation, Shutterstock

It’s been a quarter century since corn and soybeans were modified to resist the withering mists of the herbicide glyphosate. First touted as a “silver bullet” for weed control, the modified varieties and their herbicide companion were quickly and widely adopted in the corn and soybean growing regions of North America.

However, in the years that followed, the weeds targeted for eradication quietly fomented a rebellion.

A new PNAS Nexus study led by scientists at the U.S. Department of Agriculture’s Agricultural Research Service and the University of Illinois Urbana-Champaign retrospectively examines the effectiveness of glyphosate after the commercialization of transgenic crops.

Research has long indicated that weed control periods and full application rates according to label directions are essential for controlling weed populations – partial applications only kill weaker weeds and unintentionally promote a population shift towards more robust and resistant weeds. However, this PNAS Nexus study explores the need to diversify weed management systems.

Gathering data from annual herbicide evaluation trials conducted at U.S. and Canadian universities, researchers found a significant and rapid decline in glyphosate control for the seven major weed species examined.

“Our analysis represents one of the largest cumulative measures of the adaptation of weed communities to simplified weed management strategies adopted on an unprecedented scale across North America,” said Dr. Chris Landau, postdoctoral researcher at USDA-ARS and first author of the article.

“Nature did exactly what we were trying to avoid: It adapted,” said co-author Aaron Hager, professor and extension specialist in the Department of Crop and Extension Sciences. University of Illinois.

Although glyphosate provided superior weed control in the first few years, most weeds in the data set showed signs of adapting to the chemical in just two or three years. Within a decade, weeds were up to 31.6% less responsive to glyphosate, with further linear declines over time.

In addition to loss of control, the effectiveness of glyphosate has become more variable over time.

“When glyphosate-tolerant crops were first adopted, weed control was high in all environments; however, year after year, the effectiveness of glyphosate has become less consistent,” said co-author Marty Williams, USDA-ARS ecologist and affiliated professor of crop sciences.

The designs were derived from annual herbicide evaluation trials conducted at land-grant universities.

For the current study, Landau narrowed the data down to fields that tested glyphosate annually, alone or in combination with a pre-emergence herbicide. He also narrowed down the target weeds to seven main players: annual ragweed and giant ragweed, Canada fleabane, lamb’s-quarters, Palmer amaranth, velvetleaf and tuberous amaranth. Ultimately, the data set represented testing data from 11 institutions.

After documenting glyphosate control patterns and variability over time, Landau re-ran the analysis for plots where a pre-emergence herbicide had been applied before glyphosate. The results were surprisingly different.

“Adding a pre-emergence herbicide effective against targeted weed species significantly improved control and reduced glyphosate variability over time,” Landau said. “The most we have seen for any weed species is a loss of control of 4.4% per decade, compared to 31.6% for glyphosate alone. »

Landau noted that two species he tracked in the analysis, velvetleaf and lamb’s-quarters, have not yet had a confirmed case of glyphosate resistance worldwide. Yet both of these species followed the same trends as glyphosate-resistant species throughout the data set. He says herbicide pressure, or concomitant climate change, over the past 25 years may have selected for larger leaf areas or earlier emergence, which could help weeds survive glyphosate. . [Ma note : C’est nébuleux, mais c’est conforme à l’original…]

Researchers advocate diversification of chemicals, including soil and foliar applied products, crop rotation schemes and mechanical controls.


* Source : Study: Glyphosate efficacy over time, sustainable weed control strategies (

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