A new study published by the Weed Science Society of America (WSSA) reveals that fall-applied residual herbicides are highly effective in managing glyphosate-resistant (GR) Italian ryegrass. This weed poses a significant challenge to rice production in Mississippi, prompting researchers to explore advanced control strategies.
According to Jason A. Bond, an Extension/Research Professor at Mississippi State University, the research confirms that a strategic approach combining preemergence (PRE) and postemergence (POST) herbicide applications yields the best results. “For effective control, it is crucial to implement a program that begins with fall-applied residual herbicides such as dimethenamid-P (the active ingredient in Outlook ®),” Bond states.
The study involved two field trials conducted in Stoneville, Mississippi, during the growing seasons of 2021-2022 and 2022-2023. Researchers evaluated the effectiveness of various herbicide mixtures and application sequences against GR Italian ryegrass. Bond noted that timely herbicide application is vital for establishing a healthy rice crop, typically done in February or March.
In their findings, the team reported that the herbicides dimethenamid-P, pyroxasulfone (known as Zidua ®), and S-metolachlor (branded as Dual Magnum ®) alone achieved over 94% control of GR Italian ryegrass within 21 days after application. The addition of flumioxazin (marketed as Valor ® EZ) did not enhance control rates significantly 130 days after treatment.
The study also highlighted that treatments using fall-applied dimethenamid-P outperformed those with acetochlor (branded as Warrant ®) unless followed by a sequential application of clethodim (known as Select Max ®) in combination with S-metolachlor. Bond emphasized the necessity of including fall-applied residual herbicides in management strategies for controlling GR Italian ryegrass. He cautioned that without these preemergent treatments, the efficacy of S-metolachlor could diminish when targeting this resistant weed.
The complete findings on managing glyphosate-resistant Italian ryegrass in rice production can be accessed in the WSSA journal Weed Technology, which publishes peer-reviewed research on various aspects of weed management.
Weed Technology serves as a vital resource for agricultural professionals, focusing on applied research and advancements in weed control techniques. For more information, visit the WSSA website at www.wssa.net.