Patterns of herbicide resistance in Raphanus raphanistrum revealed by comprehensive testing and statistical analysis

Area of Science:

• Agricultural Science
• Plant Science
• Weed Science

Background:

• Raphanus raphanistrum poses a significant economic threat, causing an estimated $40 million in annual revenue losses in Western Australia.
• This weed species exhibits a documented history of evolving resistance to multiple herbicide modes of action.
• Understanding the extent and patterns of herbicide resistance in R. raphanistrum is crucial for effective crop management.

Purpose of the Study:

• To assess the level of herbicide resistance in 376 field-sampled populations of Raphanus raphanistrum.
• To evaluate the efficacy of 21 individual herbicides and eight herbicide mixtures with multiple modes of action against R. raphanistrum.
• To identify effective herbicide strategies for managing herbicide-resistant R. raphanistrum.

Main Methods:

• Screened approximately 104,000 individual seeds and seedlings across 7,199 resistance tests over four years.
• Tested resistance to 21 herbicides applied at recommended label rates.
• Evaluated the impact of herbicide mixtures containing two, three, or four modes of action on weed survival.

Main Results:

• Mean individual survival in populations treated with standalone herbicides was 9%, significantly reduced to 3.5% with herbicide mixtures.
• High frequencies of resistance (>50%) were observed for triasulfuron (Group 2), 2,4-D (Group 4), and diflufenican (Group 12).
• Negligible resistance was found for glyphosate (Group 9), protoporphyrinogen oxidase (PPO) inhibitors (Group 14), and pre-emergence herbicides (Groups 5 and 27).
• Binary, ternary, and quaternary mixtures of specific herbicide groups reduced resistant population frequency to 7.1%, 3.8%, and 0%, respectively.

Conclusions:

• Effective control of herbicide-resistant Raphanus raphanistrum remains challenging.
• Management strategies should leverage herbicides with modes of action not yet compromised by resistance, including pre-emergence herbicides and glyphosate.
• Integrating effective herbicide mixtures (two to four modes of action) with non-chemical control methods is essential for sustainable weed management and constraining resistance evolution.