I am getting a lot of questions about residual herbicides in soybeans this year, and that is a good thing. A lot of callers tell me which residual or pre-emergence herbicide they are using and want to know if they are doing right. In many cases they should be thinking multiple residuals.
Let’s begin with a worst-case scenario where you know you have major pigweed issues and you are going to plant Roundup Ready soybeans. Perhaps you have been in LibertyLink a couple of years and want to rotate out or you just like the Roundup Ready system. In this scenario, you definitely need to stack or overlap residuals.
I like starting out with Valor or a Valor-containing product like Envive or Enlite applied a couple of weeks before the intended planting date. This treatment is often combined with a burn-down herbicide. Hopefully you then get a rain on it and can plant into an activated treatment.
At planting, follow with a pre-emergence herbicide. You may not have any weeds emerging when you apply it, but that is our objective. There are a lot of choices and combinations. Try to get at least two modes of action. I do not recommend Prefix in this application as you need to save your fomesafen (Prefix, Reflex, Flexstar and generics) for postemergence use to avoid rotation problems.
I recommend a lot of Authority MTZ, which contains sulfentrazone and metribuzin. Often I recommend it be mixed with Dual for yet a third mode of action. Other choices are Boundary, which is Dual and metribuzin, and Canopy DF, which makes a nice tank-mix with Dual or a generic.
Some ask about just using straight Dual. You can, but I like more firepower and I want some Dual or Warrant applied in one of the postemergence applications.
When you make the first Roundup and Flexstar application, add some Dual or Warrant if any new emergence is occurring. Roundup plus Prefix can work well here, too. If things are very clean, you may consider saving the Dual or Warrant for the second application as a layby treatment. Some have a hard time getting their heads around using this much residual — especially if they are not seeing any weeds. However, that is the idea, because after you see them it is often too late. A lot of things can prevent proper timing of Flexstar, Cobra, Blazer, etc. The application window can disappear in three or four days.
In LibertyLink soybeans, use residuals! Sure, you can often get good weed control with two timely applications of Liberty, but that is not a resistance management program and dense pigweed populations will simply overpower your Liberty treatments. I talk to folks that are using two or more residuals in their Roundup Ready programs and none in their LibertyLink program. Why? The answer is we want easy and simple and we used to not need them in Roundup Ready. We do not need to go back down that road.
Shoot for 80 percent control with the residual component of your LibertyLink program. A preplant treatment of Valor or a Valor-containing product outlined above can often do it. I also like Prefix as a pre-emergence herbicide in a LibertyLink system, although there are plenty of other good choices. Consider using Dual, generic or Warrant as a layby.
If you are a first-time LibertyLink user or if you are planting them into a scenario where Roundup Ready has failed previously, I recommend the same program of stacking or overlapping residuals as outlined for a Roundup Ready program. You have a lot more postemergence firepower in a LibertyLink program, but too many things can delay proper timing.
That is a lot of money or a lot of herbicide, but if you mess around cutting corners on pigweeds they can put you out of business!