It is now “burndown time in Tennessee.” The combination of supply chain issues with the ever-increasing presence of herbicide resistant weeds has made burndown time more of a challenge in 2022. Poa and ryegrass are two very common grass weeds and are of most concern, particularly before corn planting. There are two reasons for the sketchy control of those two grasses. First, the continued evolution of glyphosate resistance in poa and ryegrass populations has made the most common burndown tankmix of glyphosate + dicamba very inconsistent. Second, we have now documented that dicamba is consistently causing glyphosate to provide poor grass control. As such our recommendation has been to change the “go-to” burndown from glyphosate + dicamba to glyphosate + clethodim.
The problem with using glyphosate + clethodim is that the burndown will miss or be weak on some broadleaf weeds, most notably glyphosate-resistant horseweed. During the meeting circuit this winter, several have asked “Is there a herbicide that is in supply that can be added to glyphosate + clethodim that will provide horseweed control while not sacrificing grass control?” This caused me to go back and examine burndown research with Elevore, Reviton and Verdict.
Elevore is fairly new burndown option that is in the auxin-mimic herbicide mode of action similar to 2,4-D and dicamba. One big plus we have seen with Elevore compared to those older auxin herbicides is the lack of grass antagonism when mixed with glyphosate.
Reviton is a new PPO-inhibiting herbicide for the burndown window. In our limited research when tankmixed with either glyphosate or clethodim we have seen good control of henbit and other winter annual broadleaves. Most notably we saw very good poa control with those tankmixes.
Those studies suggest that Elevore or Reviton should very ably replace dicamba in a burndown application without imposing appreciable loss of poa or ryegrass control from glyphosate and/or clethodim. Please keep in mind the plant back to soybean and cotton with Reviton is 14 days and corn is 0 days. The plant back with Elevore for corn is 3 days, 14 days for soybean and 30 days for cotton.
We have more extensive burndown research with Verdict. That research would indicate that Verdict does not antagonize glyphosate control of ryegrass. Poa control from this tankmix is typically pretty good. Please keep in mind the plant back to cotton after a Verdict application is 6 months. However, there is no waiting period to plant corn, grain sorghum or soybean after a 5 oz/A Verdict application.
In short, our research suggests that some of the better options that are in a little better supply by 2022 standards, are a tankmixture of glyphosate + clethodim with Elevore or Reviton or Verdict.
If glyphosate is in short supply, clethodim alone can provide good grass control with these mixtures. Please keep in mind to use at least a pint of a 2lb clethodim product to acquire the most consistent ryegrass and poa control. However, if that rate is used there is a 30-day plant back to corn. Tennessee does have a 24c special local needs label for a plant back interval on corn of 6 days for a 6 oz rate of Select Max if used for burndown.