Phone calls I have gotten over the last ten days would indicate that we may have as much as 70% of the row crop acres with some kind of first pass burndown applied prior to the rain. The number one question fielded during this period was about Leadoff herbicide. Leadoff basically is a premix of the SU herbicides rimsulfuron and thifensulfuron. There are several advantages to Leadoff in an early burndown . First it will provide several weeks residual control of winter annual weeds. Leadoff will help curtail regrowth of horseweed that has been injured by dicamba and otherwise might regrow. It also will aid in control of rye grass and poa over glyphosate alone.
On the management side do not expect Leadoff to control existing horseweed as it will need to be mixed with dicamba and glyphosate to do a thorough burndown. Please note it has a 30 day plant back to cotton and soybean after a Leadoff application. Due to this, it will likely be late to utilize any more Leadoff in fields slated for soybeans and cotton this year. This may be a mute point as I understand it is now in short supply. In corn it can be applied clear up to planting. Finally, for those areas that have established glyphosate-resistant (GR) ryegrass the glyphosate + Leadoff is not an answer. My colleagues in Mississippi Jason Bond and Tom Eubank are the experts on managing GR ryegrass and they will tell you the only way to control GR ryegrass in the spring is sequential Gramoxone applications with one of the applications tankmixed with a PSII inhibiting herbicide (i.e. atrazine, metribuzin, Cotoran).
Valor and Verdict are the other popular residual herbicides typically used in an early Burndown. Of course, Verdict will also do a good job on controlling existing horseweed. The main reason to utilize any residual herbicide in early March is for residual winter annual control. Leadoff, Valor and Verdict will all provide about the same amount of residual control for winter annuls. Please do not expect residual Palmer control from these applications. There is no residual herbicide that will typically provide any measurable Palmer amaranth control when applied most of the month of March.