In 2024, a thorough weed monitoring initiative revealed critical insights into herbicide resistance among grass weeds. Growers and advisors submitted samples of problematic weeds for testing, uncovering alarming trends and actionable findings.
Key Insights
- Herbicide resistance in meadow grasses is escalating, driven by over-reliance on spring ALS herbicides and reduced use of autumn-applied residual treatments.
- Farms grappling with ACCase-resistant wild oats, such as those treated with Axial, now have limited options, with ALS-type herbicides like Pacifica Plus or Broadway Star being teh sole effective choice—restricted to wheat crops.
- While fully herbicide-resistant brome species remain undetected, studies show a widespread decline in sensitivity among brome populations when herbicide application rates are lowered.
- Resistance testing is crucial to identify effective herbicides for specific weed populations, highlighting the need for tailored solutions.
- There is an urgent call for integrated weed management strategies to reduce dependency on increasingly ineffective and restricted herbicides.
Annual Meadow Grass: A Growing Challenge
Eight annual meadow grass populations,alongside a sensitive control group,were treated with ALS,ACCase,and glyphosate herbicides at the 2-to-4 leaf stage (Figure 1).
- Two populations,Wexford-1 and Wexford-2,remained susceptible to all tested herbicides. However, six populations exhibited resistance to ALS-Pacifica Plus.
- Resistance in these six populations was primarily due to target-site mutations. Four populations (Dublin,Louth-1,Louth-2,and Meath-2) had Pro-197 ALS gene mutations,while two (cork and Meath-1) featured Trp-574 ALS gene mutations.
- All six ALS-resistant populations also showed cross-resistance to Broadway Star, wich is not labeled for meadow grass control.
- ACCase-Centurion Max, used in winter oilseed rape, and glyphosate herbicides proved effective against all eight populations.
Figure 1: Overhead view of test trays displaying symptoms of sensitive and resistant annual meadow grass populations 30 days post-treatment with ALS (Pacifica Plus, broadway Star), ACCase (Centurion Max), and glyphosate herbicides.Broadway Star is not registered for meadow grass control. Pacifica Plus was applied at half and full recommended rates, while other herbicides were used at full label rates. Absence of plants in a square indicates full control.
rough-Stalk Meadow Grass: Emerging Resistance
Two rough-stalk meadow grass populations, tested alongside a sensitive group, were treated with accase (Axial, Falcon, Stratos Ultra, Centurion Max), ALS (pacifica Plus, Broadway Star), and glyphosate (Roundup Flex) herbicides at the 2-to-4 leaf stage (Figure 2).
Preliminary results indicate varying levels of resistance, underscoring the need for further research and adaptive management strategies.
Conclusion
The rise of herbicide-resistant weeds poses a significant threat to global agriculture. As resistance mechanisms evolve, the importance of resistance testing and integrated weed management cannot be overstated. Farmers and researchers must collaborate to develop sustainable practices that reduce reliance on herbicides, ensuring long-term crop health and productivity.
Understanding Herbicide Resistance in Rough-Stalk Meadow Grass and Wild Oats
Herbicide resistance is a growing concern for farmers and agronomists, particularly when it comes to managing weeds like rough-stalk meadow grass and wild oats. Recent studies have shed light on the effectiveness of various herbicides and the mechanisms behind resistance in these problematic species.
Rough-Stalk meadow Grass: A Case of Resistance
In a series of controlled experiments, rough-stalk meadow grass populations were treated with a range of herbicides, including ALS inhibitors like Pacifica Plus and Broadway Star, as well as ACCase inhibitors such as Axial, Falcon, Stratos Ultra, and Centurion Max. Glyphosate was also tested at recommended rates.
The results revealed that some populations exhibited resistance to ALS-Pacifica plus, with two distinct resistance mechanisms identified. One population, labeled Louth-1, displayed double mutations in the ALS gene (Pro-197 and Trp-574), while another, Louth-2, had a single mutation (Pro-197). These mutations led to cross-resistance to Broadway Star,despite the herbicide not being registered for meadow grass control.
Interestingly,ACCase herbicides and glyphosate proved effective in controlling resistant populations when applied at label rates. This highlights the importance of rotating herbicide modes of action to manage resistance effectively.
Wild Oats: A Growing Challenge
Wild oats, another troublesome weed, were also studied to assess thier resistance to ACCase and ALS herbicides. Twenty populations were treated at the 3-to-4 leaf stage with label rates of Axial, Falcon, Stratos Ultra, Pacifica Plus, and Broadway Star.
The findings were concerning: 14 out of 20 populations showed resistance to ACCase inhibitors, with all 14 resistant to Axial and Falcon. Half of these populations also exhibited resistance to Stratos Ultra. However, none of the wild oat populations displayed resistance to ALS herbicides at the time of testing.
key Takeaways for Farmers
These findings underscore the importance of adopting integrated weed management strategies. Relying solely on a single herbicide mode of action can lead to resistance, as seen in both rough-stalk meadow grass and wild oats. Farmers should consider:
- rotating herbicides with different modes of action to reduce the risk of resistance.
- Using glyphosate and ACCase inhibitors effectively, as they remain viable options for controlling resistant populations.
- Monitoring fields regularly for signs of herbicide resistance and adjusting management practices accordingly.
By staying informed and proactive, farmers can better manage herbicide resistance and protect their crops from these persistent weeds.
Understanding Herbicide Resistance in Wild Oats and Bromes: A Deep Dive
Herbicide resistance in weeds like wild oats and bromes is a growing concern for farmers worldwide. Recent studies have shed light on the effectiveness of various herbicides in combating these stubborn plants. By examining the results of controlled experiments, we can better understand how to manage resistant populations and protect crops.
wild Oats: A Test of Herbicide Efficacy
In a recent experiment, wild oats were treated with several herbicides, including ACCase inhibitors like Axial, Falcon, and Stratos Ultra, and also ALS inhibitors such as Pacifica Plus and Broadway Star. The treatments were applied at recommended rates,and the results were observed 28 days later.
Plants that were effectively controlled showed severe stunting,discoloration,and yellowing or browning of foliage,indicating complete death. These symptoms were a clear sign of accomplished herbicide application. As shown in Figure 3, the overhead view of test trays revealed the stark contrast between treated and untreated plants.
Figure 3: Overhead view of test trays showing the symptoms of suspected resistant populations of wild oats 28 days post-treatment with ACCase Axial, Falcon, Stratos Ultra, and ALS Pacifica Plus and Broadway star, all applied at the recommended rate. Full control was achieved where treated plants showed severe stunting,discoloration,or death of foliage.
Bromes: Tackling Resistance with Multiple Herbicides
Another study focused on 15 different brome species, including sterile, great, and soft bromes. These plants were sprayed at the 2-to-4 leaf stage with label rates of ACCase inhibitors (Falcon, Stratos Ultra), ALS inhibitors (Pacifica Plus, Broadway), and glyphosate (Roundup Flex).
The results were promising. all tested herbicides proved effective against the brome populations, with treated plants displaying symptoms similar to those observed in wild oats—severe stunting, discoloration, and eventual death. Figure 4 provides a visual portrayal of these findings.
Figure 4: Overhead view of test trays showing the symptoms of suspected resistant populations of bromes 28 days post-treatment with ACCase Falcon and Stratos Ultra, ALS Pacifica Plus and Broadway Star, and glyphosate, all applied at the recommended field rate. Full control was achieved where treated plants showed severe stunting, discoloration, or death of foliage.
Key takeaways for Farmers
These studies highlight the importance of using the right herbicides at the correct stages of weed growth. For wild oats and bromes, ACCase and ALS inhibitors, along with glyphosate, have shown significant effectiveness. however,farmers must remain vigilant,as resistance can develop over time. Rotating herbicides and integrating other weed management practices can help mitigate this risk.
As one researcher noted, “Where treated plants showed severe stunting, discoloration, or yellowing and browning of foliage, full control was achieved.” This underscores the critical role of timely and accurate herbicide application in maintaining healthy crops and sustainable farming practices.
What specific post-treatment observations in the images highlight the importance of selecting herbicides with different modes of action for effective weed management?
Post-treatment. The images highlight the varying levels of control achieved with different herbicides, emphasizing the importance of selecting the right herbicide and mode of action for effective weed management.
Key Findings on Wild Oats Resistance
The study revealed that 14 out of 20 wild oat populations tested exhibited resistance to ACCase inhibitors, such as Axial and Falcon.Half of these resistant populations also showed resistance to Stratos Ultra, another ACCase inhibitor. However, none of the populations displayed resistance to ALS inhibitors like Pacifica Plus and Broadway Star at the time of testing. This suggests that ALS inhibitors remain a viable option for controlling wild oats,at least in the tested populations.
Implications for Weed Management
the findings underscore the critical need for integrated weed management strategies. Over-reliance on a single herbicide or mode of action can accelerate the progress of resistance, as demonstrated by the widespread resistance to ACCase inhibitors in wild oats. farmers are encouraged to:
- Rotate Herbicides: Use herbicides with different modes of action to reduce the selection pressure on weed populations and delay the development of resistance.
- Combine Chemical and Non-Chemical Methods: Incorporate cultural practices,such as crop rotation,tillage,and mechanical weed control,alongside herbicide applications to manage resistant weeds effectively.
- Monitor Fields Regularly: Keep a close eye on weed populations for signs of resistance and adjust management practices accordingly.
- Use Herbicides Strategically: Apply herbicides at the correct growth stages and rates to maximize efficacy and minimize the risk of resistance development.
Conclusion
Herbicide resistance in weeds like wild oats and bromes poses a critically important challenge to modern agriculture. However, by understanding the mechanisms of resistance and adopting integrated weed management practices, farmers can mitigate the impact of resistant populations and protect crop yields. regular monitoring, strategic herbicide use, and diversification of control methods are key to staying ahead of this evolving issue.
For more detailed insights and visual evidence, refer to the figures and captions provided in the article, which illustrate the symptoms of herbicide resistance and the effectiveness of different treatments.
