Weed Science Society of America
Research published by the Weed Science Society of America (WSSA) has revealed that fall-applied residual herbicides are highly effective in controlling glyphosate-resistant (GR) Italian ryegrass. This finding is particularly significant for rice producers in regions like Mississippi, where this weed poses substantial challenges to crop yields.
Jason A. Bond, an Extension/Research Professor at Mississippi State University, led the research team at the university’s Delta Research and Extension Center. According to Bond, the study highlights that the most effective strategy for managing GR Italian ryegrass involves a combination of preemergence (PRE) and postemergence (POST) herbicide applications. He emphasizes that utilizing fall-applied residual herbicides, such as dimethenamid-P (the active ingredient in Outlook®), is critical for effective control.
To assess the efficacy of these herbicides, Bond and his team conducted two separate field studies in Stoneville, Mississippi, during the periods of 2021 to 2022 and 2022 to 2023. The first study, known as the Herbicide Mixture Study, evaluated the control of GR Italian ryegrass using various mixtures of fall-applied residual herbicides. The second study, termed the Sequential Herbicide Application Study, focused on the effectiveness of sequential applications combining PRE and POST herbicides.
In Mississippi, timely herbicide application is essential for establishing a strong rice crop. Bond explains that preplant herbicide applications, commonly conducted in February or March, play a crucial role in minimizing unwanted vegetation during the seeding process.
The findings from the Herbicide Mixture Study indicated that treatments with dimethenamid-P, pyroxasulfone (known as Zidua®), and S-metolachlor (trademarked as Dual Magnum®) achieved over 94% control of GR Italian ryegrass just 21 days after treatment. Notably, adding flumioxazin (sold as Valor® EZ) to the herbicide mix did not enhance control levels at 130 days after treatment.
In the Sequential Herbicide Application Study, treatments involving fall-applied dimethenamid-P outperformed those with acetochlor (trademarked as Warrant®), except in cases where fall-applied acetochlor was followed by a sequential application of clethodim (marketed as Select Max®) combined with S-metolachlor.
Bond concludes that the research underscores the necessity of incorporating fall-applied residual herbicides into GR Italian ryegrass control programs in Mississippi. He cautions that without such applications, the efficacy of S-metolachlor could diminish when used alongside clethodim targeting GR Italian ryegrass. Furthermore, minimal benefits were observed when residual herbicides were added to a sequential clethodim application.
For further details on managing glyphosate-resistant Italian ryegrass in rice production, refer to the WSSA journal article titled “Glyphosate-resistant Italian ryegrass (Lolium perenne ssp. multiflorum) control in preemergence and postemergence programs containing mixtures of residual herbicides.” This research contributes valuable insights into the ongoing challenges faced by agricultural producers in effectively managing weed resistance.
The Weed Technology journal, published online by Cambridge University Press, focuses on original research related to weed management and its implications for agricultural systems. For more information, visit wssa.net.
