There have been a number of reports on disappointing burndown applications that were applied during that cold stretch, 3 to 4 weeks ago, when nighttime temperatures were in the 20s. The herbicides that performed poorly were some combination of systemic herbicides glyphosate, dicamba, clethodim and Leadoff.
In hind sight, it is not surprising those herbicides did not perform well as temperatures were too cold for optimal performance. On the other hand, it is notable that there were no reports of poor burndown performance with Gramoxone, Reviton and Verdict. Those contact herbicides are not as prone to being impacted by cold night temperatures as systemic herbicides. This is something to remember for the 2023 burndown season.
Generally speaking, systemic herbicides do not typically work well on weeds that escaped early herbicide applications. The contact herbicides mentioned above would be the best candidates to burndown those escaped winter annual weeds.
One final note is the new PPO-inhibiting herbicide Reviton mixed with glyphosate has done a good job burning down many winter annual weeds like henbit and poa. Unfortunately, it is weak on horseweed. This was very apparent in growers’ fields as well as our research this year. One will need to tankmix in 8 ozs of dicamba with the Reviton and glyphosate to pick up horseweed.