Research Highlights

2021 Weed Control Options Come into Clearer View

Kentucky Soybean

The recent announcements of the EU approval of RR2XtendFlex (RoundupReady 2 XtendFlex) soybean and EPA approval of three dicamba products has brought a clearer view of soybean weed control options available to Kentucky farmers for 2021. Prior to these two announcements, the waters were murky with unknowns of if the flexibility of the RR2Xtendflex system would be available and if any dicamba formulations would be available to spray on any dicamba tolerant soybean acres. With the recent announcement came answers and clarification, but also prompted a few more questions and restrictions.

The most recent event to occur was the approval of Xtendimax (Bayer), Engenia (BASF), and Tavium (Syngenta) for applications to dicamba-tolerant (DT) soybean. The three labels stayed largely unchanged from previous versions although crops outside of DT soybean and DT cotton have been removed from the labels. Restrictions of nozzles, tank mixes, sprayer speed, boom height, wind speed, and temperature inversions remain the same as previous labels. 

The restrictions that have changed are rate changes for Xtendimax burndowns, application cutoff date/growth stages, increases in buffer requirements, and the new requirements of a volatility reduction agent or buffer agent. Each change is described below:

• Xtendimax can only be applied at a rate of 22 fl oz/a per application, regardless of application timing. Previous labels allowed up to 44 fl oz/a Xtendimax for preplant/burndown applications, but that rate is no longer labeled.
• All three labels have a federal cutoff date of June 30th and no application can be made after that date. The Xtendimax label also indicates a cutoff soybean growth stage of R1, whereas the Tavium label has a soybean growth stage cutoff of V4. In both cases whichever occurs first (date or growth stage) takes precedent. The Engenia label does not include a cutoff growth stage, thus June 30th is the cutoff for this product.  
• Downwind buffers have been extended from 110 ft. in the previous labels to 240 ft. in the new labels. Similar to previous labels, these buffers can be included in directly adjacent roads, mowed grassy areas, corn fields, DT soybean fields, fields prepared for planting, and/or areas covered by a building. THIS BUFFER IS NOT INTENDED FOR PROTECTION OF DICAMBA SENSITIVE CROPS, THE LABELS REMAIN THE SAME IN THAT APPLICATIONS CANNOT BE MADE IF THE WIND IS BLOWING TOWARDS A SENSITIVE CROP SUCH AS NON-DT SOYBEAN, TOBACCO, VINEYARDS, AND TOMATOES.
• These buffers can be reduced with the use of hooded/shielded sprayers or other approved drift reduction technologies (DRT), as outlined on each label website.
• Areas in which endangered species are present may need a 310 ft. downwind buffer plus a 57 ft. omni-directional buffer. A list of these areas can be found on the Bulletins Live 2 website.  
• The addition of a volatility reduction agent (VRA) or buffer agent is also required for all three labels in addition to drift reduction agents (DRA) that were required by previous labels. The list of approved VRA or buffers can be found on each respective products label website.

As in the past, dicamba-specific training will still be required prior to application of Xtendimax, Engenia, and/or Tavium. This training will be offered by the registrants and will largely be available online.

The additional restrictions bring some clarification to past issues of the previous dicamba labels, but the additional restrictions certainly do not make their application easier. The extension of the downwind buffer to 240 ft. may cause havoc as many Kentucky fields are surrounded by trees and thus the buffers will have to be placed within the production field being sprayed. While the distance in necessary to protect our natural resources and endangered species, 240 ft. can add up to numerous acres very quickly. In some cases, the area will be large enough for applicators/farmers to question the feasibility of applying the product to a given field. 

The addition of the June 30th cutoff date places a hard deadline on applications, whereas past labels in which growth stages were used allowed many applications to continue to occur in the hot and humid months of July and August. Weather conditions in Kentucky in July and August simply are not ideal for dicamba applications in any crops, not to mention the numerous sensitive crops that are out during those time of year including tobacco. This cutoff date does however eliminate a lot of possible uses for double crop soybeans that likely will not be planted until late June and early July, so growers may need to seek an alternative herbicide programs for double crop soybean acres.

Despite the increase in restrictions of the new dicamba labels, the announcement of these labels comes on the heels of the approval of RoundupReady 2 XtendFlex soybean by the EU and thus full clearance for commercial production of those soybean varieties. The availability of RR2XtendFlex soybean varieties brings versatility to the Xtend platform that can be compared to its closest competitors. The XtendFlex soybean offers resistance to glyphosate and dicamba the same as RR2Xtend, but also offers glufosinate resistance. 

The addition of glufosinate offers postemergence flexibility for farmers who are dealing with glyphosate resistant broadleaf weeds such as Palmer amaranth or waterhemp. The biggest fallacy, in my opinion, of the RR2Xtend soybean varieties was that farmers were largely married to dicamba for postemergence applications when dealing with waterhemp and Palmer amaranth, especially with the increasing incidence of PPO-resistance in these two weed species. 

In many cases a farmer/applicator was stuck in between a rock and a hard place when deciding when to apply dicamba under restrictive conditions and a rapidly growing weed. The addition of glufosinate offers a bit more flexibility and can allow a farmer to make an effective postemergence application of glufosinate if environmental conditions or surrounding crops do not allow for a timely application of dicamba. It must be said, though, that glufosinate is very capable of drifting the same as any other herbicide and thus if the wind is blowing at high speeds towards a sensitive crop no herbicide application, glufosinate, dicamba, or other should be applied.

As has been the message from University of Kentucky Weed Science in the past, the specific dicamba formulation one wants to apply and/or when to apply glufosinate matters less than the residual herbicide applied. Anybody choosing to raise RR2Xtendflex soybean who is dealing with Palmer amaranth or waterhemp must remain vigilant and apply robust preemergence herbicides. Research supported by the Kentucky Soybean Board has shown that even with the flexibility of the RR2XtendFlex soybean platform, the use of a residual herbicide with two to three effective sites of action is more influential on end of season waterhemp and Palmer amaranth control than the choice or sequence of postemergence herbicides. This message applies to all herbicide-tolerant soybean systems, and will continue to be the message for these two troublesome weeds.

Up to the recent two approvals of RR2XtendFlex soybean and Xtendimax, Engenia, and Tavium there were a lot of unknowns in weed control going into 2021. These recent approvals have brought a lot clarification to what farmers will have available for weed control in 2021 and their options are now fairly large, which is great for soybean farmers.

Published: Feb 15, 2021