By: Dr. Mark Loux, OSU Extension
Sometimes you’d like the s**t to stop hitting the fan just long enough to get cleaned up, but you can’t get a break. Like when you’re in the middle of an endless pandemic, a worldwide shipping fiasco, herbic ide scarcities and price increases, and parts shortages. And just when you had it worked out to use Enlist herbicides on Enlist soybeans for 2022 so you wouldn’t have to deal with dicamba, their use is no longer legal in your county. We’re trying to find something reassuring to say here, but there’s not much. The USEPA issued a new seven-year registration for Enlist One and Enlist Duo, valid through January 2029. Changes include a revised application cutoff for soybeans, “through R1” that replaces “up to R2” on previous labels, and the addition of a slew of spray nozzles to the approved nozzle list. The most significant change for Ohio is that due to changes in Endangered Species information, Enlist One and Enlist Duo cannot be used in 12 Ohio counties: Athens, Butler, Fairfield, Guernsey, Hamilton, Hocking, Morgan, Muskingum, Noble, Perry, Vinton, and Washington. We contacted Corteva to see if this was likely to change anytime soon, and got no assurances of this, although the PR information they have distributed indicates it is possible.
This really couldn’t happen at a worse time for growers in these counties. We lack solid information on herbicide availability and price, and it’s a fluid situation, but it appears that glyphosate and glufosinate can be in short supply, and prices high. Glyphosate resistance in key weed species makes us dependent on POST soybean herbicide systems based on use of glufosinate (Liberty etc), dicamba (XtendiMax/Engenia), or 2,4-D (Enlist One/Duo). The Enlist system allows use of glyphosate, glufosinate, and 2,4-D, and combinations of these. While Enlist soybeans are tolerant of other 2,4-D products, Enlist One and Duo are the approved 2,4-D products for all POST applications to Enlist soybeans, and any preplant or preemergence applications that occur less than 7 days before planting or anytime after planting. As far as we know, this prohibition of use does not apply to legal uses of other 2,4-D products. Some things to consider here:
– Some growers/applicators were planning on omitting glyphosate from burndown and/or POST applications. In the Enlist system, this increases the overall importance of the 2,4-D in these applications. Where the Enlist products cannot be used, revaluation of the mixture is warranted. It may be necessary to use glyphosate, or an alternative 2,4-D product in the burndown (with a 7-day wait to plant), or other herbicides, such as Sharpen or Gramoxone.
– The most obvious replacement for Enlist products in POST applications is glufosinate since glyphosate won’t control most populations of ragweed, waterhemp, or marestail. Growers going this route should check on availability and price immediately, since supply seems to be finite. For those in the 12 counties who are unwilling or unable to use glufosinate, the Enlist soybean essentially becomes a RoundupReady soybean with respect to herbicide use.
– Most users of glufosinate supplement the grass control by including either glyphosate, or a POST grass herbicide such as clethodim. Glufosinate is weak on barnyardgrass and yellow foxtail, volunteer corn, and large grasses in general.
– While spray volume and nozzle type are not that critical for effectiveness of 2,4-D and glyphosate, glufosinate requires these to be optimized to maximize activity. Most growers tell us that for glufosinate, 20 gpa works better than lower spray volumes. The nozzles that work well to minimize off-target movement of Enlist products may not be optimum for glufosinate.
– Where 2,4-D cannot be used in the POST, the effectiveness of the residual herbicides used becomes more important. Glufosinate applied alone or with just a grass herbicide can be less effective on certain broadleaf species, and large weeds in general, compared with mixtures of 2,4-D with glufosinate or glyphosate. We recommend using residual herbicides at planting, and possibly increasing herbicide rates and the overall complexity of the mixture.
Information we have received from Corteva includes several documents with explanation of label changes and restrictions, and supplemental labels for Enlist One and Enlist Duo. Aside from this, we don’t know any more than anyone else.