Managing the evolution of herbicide resistance

Area of Science:

• Agricultural Science
• Evolutionary Biology
• Ecology

Background:

• Herbicide-resistant (HR) weeds threaten agricultural sustainability and profitability.
• Understanding the large-scale evolution of weed resistance, particularly glyphosate resistance in Amaranthus tuberculatus (common waterhemp), is critical but poorly understood.
• This study investigated glyphosate resistance in common waterhemp across agricultural landscapes.

Purpose of the Study:

• To analyze the factors influencing the evolution and spread of glyphosate resistance in common waterhemp at a landscape scale.
• To identify weed and herbicide management practices associated with glyphosate-resistant (GR) common waterhemp occurrence.
• To evaluate the effectiveness of herbicide mixing in managing GR weed populations.

Main Methods:

• Utilized landscape, weed, and management data from 105 central Illinois grain farms.
• Analyzed over 500 site-years of herbicide application records.
• Correlated GR A. tuberculatus occurrence with glyphosate application frequency, herbicide mechanism of action (MOA) turnover, and the number of MOAs used per field per year.

Main Results:

• Glyphosate-resistant (GR) A. tuberculatus was most prevalent in fields with frequent glyphosate applications and high annual rates of herbicide mechanism of action (MOA) turnover.
• Fields utilizing fewer MOAs per year also showed a higher incidence of GR A. tuberculatus.
• Combining different herbicide MOAs during application, through herbicide mixing, was found to reduce the likelihood of GR A. tuberculatus.

Conclusions:

• Examining evolutionary processes at relevant spatial scales is essential for effective weed management.
• While herbicide mixing can delay the evolution of glyphosate resistance and other HR weed traits, it is unlikely to prevent it entirely.
• Sustainable long-term weed management necessitates diversified practices that minimize selection pressure for herbicide resistance.