2,4-D choline (Enlist One) and dicamba (Xtendimax) will be tankmixed with glyphosate for burndown treatments under different scenarios. Applications will be made 10 to 14 days before planting with no rye; applied 4 weeks before planting without rye; applied 4 weeks before planting followed by an application 10 to 14 days before planting; and with cereal rye, an application 10 to 14 days before planting. A comparison treatment of Enlist One plus glyphosate 4 weeks before plant to eliminate all emerged weeds followed by Trivence plus glyphosate plus COC 10 to 14 days preplant to control weeds present at planting and provide the residual (is it possible to eliminate the second application of Enlist One?). Trivence (Valor+chlorimuron+metribuzin) will be included with the last herbicide application for each treatment to provide residual control as part of a full-season approach to weed control. By using UD’s research planter, soybeans with the appropriate herbicide tolerance can be used for each treatment. All herbicides will be applied at 20 g/A; with appropriate spay nozzles; at maximum allowable rates; and with appropriate adjuvants. Plots will be evaluated for crop response and weed control on a weekly basis after initial application. Plots will be harvested to determine impact of
weed control on yield. However, using multiple varieties may not allow comparison of yields across the various herbicide programs.

This project will examine various postemergence approaches for Enlist soybeans. Applications will be made to weeds slightly larger than the recommended size for treatment (8 to 10 inches tall) to help separate treatment differences. Enlist One will be tankmixed with glyphosate, glufosinate, Reflex, Assure II and Select. In addition, Liberty will be applied with a second application of Enlist One plus glyphosate as a two-pass POST program. All herbicides will be applied at 20 g/A; at maximum allowable rates; and with appropriate adjuvants. Appropriate spray nozzles will be used for Enlist and for Xtendimax treatments based on label requirements. Plots will be evaluated for crop response and weed control on a bi-weekly basis after initial application. Plots will be harvested to determine impact of weed control on yield.

1) Utility of Enlist versus Xtend soybeans for burndown weed control.
2) Evaluate the best use of Enlist soybean traits for postemergence weed control.

Reports of this study will be disseminated through extension presentations and be used to develop weed control recommendations. Research plots will be highlighted on field tours at the Research and Education Center. An annual report will be available through the UD Weed Science Website (http://extension.udel.edu/ag/weed-science/weed-science-reports/).

Updated August 1, 2021:

View uploaded report

Updated February 10, 2022:

View uploaded report

Enlist soybeans have been developed to be resistant to 2,4-D, glufosinate, and glyphosate herbicides. With resistance to three different herbicide modes of action, these soybeans provide more flexibility for weed control options than were previously available. While 2,4-D could be used as a pre-plant herbicide, applications were not permitted within 7 to 15 days prior to planting and at lower use rates. UD Weed Science Research recommend a 2,4-D use rate 1 lb acid equivalent, which limited treatments to at least 20 days before planting (depending on formulation). Enlist soybeans can be treated with this higher rate at any time, including at planting. This may allow for delayed burndown applications while still obtaining good to excellent weed control.

Enlist soybeans can be treated postemergence with Roundup (glyphosate), Liberty (glufosinate), and/or Enlist (2,4-D choline). Due to the concern of 2,4-D offtarget movement and limited availability of Enlist research projects; UD Weed Science has not had as many opportunities to test Enlist soybeans as Xtend soybeans. Research in the mid-West over the past 2 to 3 years have shown that volatility of 2,4-D choline (the salt formulation in Enlist herbicide) is at a much lower risk than dicamba (in Xtendimax or Engenia). Physical movement (drift with small droplets and wind) is still a concern, but volatility may not be as much of a concern. Evaluating tankmixtures of glyphosate and glufosinate, or glufosinate plus 2,4-D is needed to understand the strength and weaknesses of these mixtures.

Liberty plus Enlist appears to be a better tankmixture than Liberty plus Xtendimax. Enlist allows for a smaller droplet size than Extendimax/Engenia and the smaller droplet size will improve the spray coverage of Liberty and in turn improving its
control. Note UD research has found very similar results between Engenia and Extendimax so we do not make a distinction between the two.

A limited number of studies in the mid-West have shown the potential for reduced grass control when glyphosate is tankmixed with Enlist One. In addition, glufosinate (the third trait in Enlist soybeans) is not very effective on grasses, so additional research is needed to ensure grass control is adequate with this trait.

Xtend soybeans (dicamba-tolerant) have been studied more extensively by UD Weed Science through funding by BASF, Monsanto/Bayer, DuPont, and Syngenta. However, most of the research projects have focused on postemergence weed control. Local research comparing 2,4-D with dicamba as a burndown herbicide has not be done. Identifying the strength and weaknesses of these herbicides for burndown of difficult to control weeds such as marestail/horseweed or primrose, is important to look to compare these herbicide traits. How does dicamba or high rates of 2,4-D compare for a single burndown application at planting when these problem weeds are in the field? Is there a difference/advantage to using dicamba or 2,4-D when late-terminated cover crops are used?