Steckel: Some New Thoughts on Burndown Strategy

For the last two decades, dicamba has been used extensively as a pre-plant burndown on almost all Tennessee cotton and soybean acres – often used at 8 to 12 oz/A of a Clarity-type product, 14 days before planting.

I know it has become tradition to use it in this fashion, but I believe this should be changed for three reasons:

• First, the reason for all the dicamba use in a burndown was to target horseweed. Of course, at the time, it was a weed with no effective in-season herbicide option for control. However, that is no longer the case. Most soybean and cotton acres planted in Tennessee are planted to an Xtend variety and the rest are planted to Enlist varieties. Depending upon which technology, horseweed can now be easily removed in crop with a dicamba, 2,4-D or Liberty application.
• Second, it is becoming abundantly clear that the decades-long use of dicamba plus glyphosate as a burndown has selected for weeds that can survive – and indeed thrive – in that environment. Ryegrass, poa, junglerice, barnyardgrass and goosegrass are all now regularly escaping burndown applications of dicamba plus glyphosate. I would suggest glyphosate or glyphosate tankmixed with clethodim to have the best chance for success controlling those grasses before the crop emerges. Also consider using a residual that has good grass activity. Verdict would a good option here, as it has both burndown activity and grass residual. Others like Anthem Max, Dual Magnum and Zidua would also be good choices.
• Third, from a financial standpoint, I would save the money on using dicamba before planting or even at planting, as it will likely hinder grass control. In 2019, grasses (and Palmer amaranth in some fields) often escaped the initial POST application of dicamba plus glyphosate. As such, there were often second or third POST applications needed to control those escapes. That money used on dicamba in the early burndown could be put to better use on those follow-up applications. Recent greenhouse screens of Palmer amaranth, junglerice and barnyardgrass plants grown from seed collected from those escapes in 2019 would suggest that grass and Palmer control will be even more of an issue this spring.

It is now very apparent that dicamba plus glyphosate have taken a step backwards with respect to consistent control of many grasses and, in some cases, Palmer amaranth. Therefore, starting clean has never been more important. Gramoxone used right behind the press wheel will be the most important herbicide used on all of our no-till soybean and cotton acres in 2020.