Is there a future for pre-emergence dicamba in soybean production?

Sachin Dhanda, Weed Science Postdoctoral Researcher, Navjot Singh, Weed Science Graduate Research Assistant, and Debalin Sarangi, Extension Weed Specialist

In February 2024, the United States Environmental Protection Agency (EPA) vacated the registrations of XtendiMax, Engenia, and Tavium, three dicamba-containing products previously approved for postemergence broadleaf weed control in dicamba-resistant soybean, following a court ruling. As a label is the law, without one, it is illegal to apply these products under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). This decision raised significant concerns among farmers, who were already struggling with limited herbicide options to manage tough-to-control weeds. However, other dicamba products, such as Clarity or Status, are allowed for application in corn.

Using Clarity as an example, this product can be used in corn from preplant, pre-emergence to post-emergence timings. In soybean, Clarity may be applied preplant, provided that a minimum of 1-inch of rainfall or irrigation occurs after application. Additionally, a waiting interval of 14 to 28 days must be observed for application rates between 8 and 16 fl oz/A. If Clarity is intended for use in soybean, be sure to follow the required annual rainfall restrictions outlined on the product label.

If allowed in the future, can we use dicamba as pre-emergence in dicamba-resistant soybean? With this question in mind, a study was conducted from 2021 to 2023 in three Upper Midwest states, including Minnesota, North Dakota, and Wisconsin, to evaluate the use and efficacy of dicamba (Xtendimax) when tank mixed with other soil residual herbicides in dicamba-resistant soybean. A detailed research results can be found in a paper published recently in Frontiers in Agronomy (Dhanda, Singh, Ikley, DeWerff, Werle, and Sarangi). The pre-emergence herbicide treatments tested in this field research are included in Table 1.

Table 1. List of pre-emergence herbicide treatments with their rates.

Herbicidea,b	Rate (fl oz/A)
Untreated check	-
Warrant	48
Warrant Ultra	50
Warrant + Mauler	48 + 8
Valor EZ	2
Fierce EZ	6
Authority MTZ	10
Warrant + XtendiMax	48 + 22
Warrant Ultra + XtendiMax	50 + 22
Warrant + Mauler + XtendiMax	48 + 8 + 22
Valor EZ + XtendiMax	2 + 22
Fierce EZ + XtendiMax	6 + 22
Authority MTZ + XtendiMax	10 + 22
XtendiMax - only	22

^aAll XtendiMax-based treatments had VaporGrip Xtra at 20 fl oz/acre as a volatility-reducing agent.
^bWarrant Ultra treatment was not applied at the North Dakota site.

Weed control

The research results showed that tank mixing Xtendimax with other pre-emergence herbicides improved the control of waterhemp, giant ragweed, common ragweed, common lambsquarters, kochia, and velvetleaf in all three states (Figure 1).

Figure 1. Addition of dicamba (Xtendimax) with other pre-emergence herbicides improved weed control. Triangles in the boxplot represent replicated data points, the cross (x) represents the mean weed control, and the solid black line within each box represents the median. Mean weed control comparisons are presented as significant at p < 0.01 (**) and p < 0.001 (***). The figure is from Dhanda et al. (2025).

In Minnesota, all pre-emergence herbicides provided waterhemp control ranging between 49 and 69% at 21 days after treatment; however, tank mixing Xtendimax with these herbicides improved that control to 69-76%. For example, Fierce EZ and Authority MTZ alone provided 49% and 51% control of waterhemp at 21 days after treatment, respectively. However, tank-mixing XtendiMax with these herbicides increased control to 69% and 76%, respectively. Xtendimax alone as pre-emergence resulted in 60% waterhemp control in Minnesota (Figure 2). A similar trend was observed in other states (Figure 3).

Figure 2. Weed control in Rosemount, Minnesota, in 2022 using Xtendimax as pre-emergnece: (A) Non-treated control, (B) Fierce EZ at 6 fl oz/A, (C) Fierce EZ at 6 fl oz/A + Xtendimax at 22 fl oz/A, and (D) Xtendimax alone at 22 fl oz/A.

Figure 3. Waterhemp control at Minnesota (A) and North Dakota (B) sites at 21 days after herbicide application. Bars with different letters for each weed species show treatments that were significantly different (P < 0.05).

Dicamba pre-emergence in dry conditions

Dicamba is highly soluble in water and has low soil binding properties; therefore, it remains available to plants even when soil moisture is limited. Consequently, using dicamba as a pre-emergence along with other residual herbicides under dry conditions can provide enhanced control of broadleaf weeds. However, due to the same property, dicamba can leach or degrade faster following a significant rain event, leading to shorter residual control. This research was conducted between 2021 and 2023, when soil moisture was somewhat limited in the late spring when pre-emergence treatments were made.

Summary

• The product labels for XtendiMax, Engenia and Tavium are still vacated, and pre-emergence or over-the-top applications of dicamba are still prohibited in dicamba-resistant soybean. So, DO NOT use these products.
• This research demonstrated that, if allowed in the future, PRE application of dicamba (XtendiMax in this study), when tank-mixed with other residual herbicides, can effectively control problem weeds. Even in cases where complete control was not achieved, the addition of dicamba improved weed suppression compared to using residual herbicides alone.
• Because dicamba is highly water-soluble, its residual activity may be shorter than that of other residual herbicides and can diminish rapidly following heavy rainfall. However, this same property may offer advantages under dry conditions, where dicamba can provide added benefits when soil moisture is limited.
• Under hot, dry, and windy conditions, dicamba is more prone to volatilization or drift, therefore, precautions must be taken during spraying.
• More details of this study can be found in “Dicamba-based preemergence herbicide tank mixtures improved residual weed control in dicamba-resistant soybean” https://doi.org/10.3389/fagro.2025.1576547.

Additionally, year-wise reports and visuals from the Wisconsin site can be found at:

2021: https://wiscweeds.info/images/2021%20Research%20Report/XtendiMax%20Paired%20Soil%20Residual%20Herbicide%20Programs.pdf

2022: https://wiscweeds.info/images/2022%20Research%20Report/XtendiMax%20Paired%20Soil%20Residual%20Herbicide%20Programs.pdf