Dicamba Update from LSU AgCenter Weed Scientists
By Donnie Miller, Daniel Stevenson and Prashant Jha
LSU AgCenter
As you are aware, the EPA existing stocks order resulting from the vacated labels of Xtendimax, Engenia, and Tavium herbicides in February of this year ended for soybean on June 30 and July 30 for cotton in Louisiana. Bayer (Xtendimax), BASF (Engenia), and Syngenta (Tavium) have each submitted proposed labels for EPA review and approval this summer 2024. Announcements for each are linked below. Each has modifications to the previously approved labels. The biggest change will be for applications in soybean, where Bayer will NOT ALLOW ANY over-the-top application (only prior to soybean emergence) while BASF and Syngenta will allow over-the-top application through the V2 growth stage but no later than June 12. For cotton, BAYER and BASF will allow over-the-top application until July 30 while Syngenta will allow over-the-top application through the 6-leaf growth stage but no later than July 30. Again, these are proposed labels and modifications presented are subject to final EPA approval.
https://www.epa.gov/pesticides/epa-opens-public-comment-period-proposed-dicamba-herbicide-syngenta
https://www.epa.gov/pesticides/epa-opens-public-comment-period-proposed-dicamba-herbicide-basf
As a result, the question begs “will we have dicamba for use in DT (dicamba tolerant) crops in 2025??” It is our understanding that once the comment period for each herbicide ends, EPA has a 15-month period to make a final decision on registration of the dicamba product. The agency can make a decision any time prior to that or take their entire allotted review timeframe. The earliest to submit a proposed label was Bayer in late May. If you add the comment period that followed and 15-month review period, you are looking at very late fall of 2025/early winter of 2025 before that product may be approved. Again, a decision can occur within the 15-month review period so approval may be granted in time for the 2025 growing season. Given the labels were vacated in February because of litigation against EPA for failure to follow outlined procedure in-regards-to comment period prior to label approvals in 2020, an abundance of caution and deliberation will undoubtedly be utilized by the federal agency in this process of registration.
What does weed control look like in the absence of approved dicamba formulations for use in DT cotton and soybean? Herbicides with soil residual activity will continue to play a vital role in pre-plant, at planting, and postemergence (layered residual) programs. Including strong residual herbicides (multiple modes of action) is vital in reducing the population of many weeds, in particular annual grasses and pigweed species, thereby reducing early-season competition and making postemergence applications more timely and effective (targeting smaller weeds) in-season. They are also a first line of defense against herbicide resistance by reducing weed emergence and selection pressure on postemergence herbicides, with the goal to prevent escapes and additions to the soil weed seed bank. Several effective options are available in both cotton and soybean and rates and weed control efficacy are listed in the 2024 LSU AgCenter Suggested Chemical Weed Control Guide:
Postemergence options in-season will continue to include Roundup Ready, Liberty Link, and Enlist weed control systems in both crops. Combinations of glyphosate, glufosinate, and 2,4-D choline in two- or three-way mixes have resulted in excellent control of most resistant and non-resistant grass and broadleaf weeds infesting these two crops. Combinations with other labeled herbicides can also improve control on select weeds and provide soil residual activity (see links above: inclusion of approved dicamba products reflects use in the 2024 growing season only and is subject to EPA approval in 2025).
It is important to remember that although an approved dicamba formulation may not be available for use in DT cotton and soybean in 2025, seed will be available that does contain the tolerance trait to dicamba and as always, it is ILLEGAL to apply any unapproved dicamba formulation to these varieties. In addition, the Enlist trait does NOT impart tolerance to dicamba. It is also important to keep in mind that decisions on seed needs may have to be made very early (early fall of 2024) to ensure seed availability as the industry adjusts to the potential impact of a dicamba free 2025 growing season.
Please feel free to contact us with any questions regarding this email and weed management decisions in cotton and soybean for the 2025 growing season.
Donnie Miller, Professor and Weed Scientist, LSU AgCenter Northeast Research Station (318-614-4044)
Daniel Stephenson, Professor and Weed Scientist, LSU AgCenter Dean Lee Research Station (318-308-7225)
Prashant Jha, Professor and Weed Scientist, LSU School of Plant, Environmental, and Soil Sciences (406-647-1427)