In February 2024, the U.S. Environmental Protection Agency (EPA) vacated registrations for over-the-top (OTT) use of dicamba on dicamba-resistant cotton and soybean following a federal court ruling that cited procedural deficiencies in the registration process. This ruling effectively halted the use of several dicamba-based herbicides—including Bayer’s XtendiMax, BASF’s Engenia, and Syngenta’s Tavium—for postemergence applications, triggering uncertainty across U.S. agriculture.
The decision has left many soybean and cotton growers with fewer effective chemical tools to combat herbicide-resistant weeds such as waterhemp, Palmer amaranth, and kochia, which have increasingly challenged crop yields in the Midwest and South.
Despite regulatory setbacks, off-target movement and volatility remain the most critical concerns with dicamba use, particularly during OTT applications. However, emerging research suggests that preemergence (PRE) applications of dicamba, especially when tank-mixed with soil residual herbicides, could offer a viable path forward—minimizing drift potential while retaining weed control efficacy.
To explore this potential, multi-year field trials were conducted between 2021 and 2023 across Minnesota, North Dakota, and Wisconsin. These studies, supported by university agronomy departments and industry collaborators, assessed the effectiveness of dicamba-based PRE herbicide mixtures in dicamba-resistant soybean production systems.
Key findings include:
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Minnesota (2022–2023):
PRE dicamba tank mixes improved waterhemp control to 72%, compared to 59% for residual herbicides alone at 21 days after treatment (DAT).
Common lambsquarters and giant ragweed control improved by 17% and 20%, respectively, with weed densities reduced by at least 50%. -
North Dakota (2022–2023):
Waterhemp control jumped from 74% to 97% at 21 DAT when dicamba was added to the mix.
Kochia control improved by 23%, highlighting dicamba’s continued relevance against this difficult-to-manage species. -
Wisconsin (2021–2022):
Dicamba-based tank mixes achieved 96% control of common ragweed and 83% of velvetleaf, versus 83% and 73% without dicamba, respectively.
