It’s time to start thinking about prepaying inputs for the coming year and part of that is putting together plans for how we’re going to keep fields clean and to be able to know what herbicides we want to purchase and at what rates. In the weed management information accumulated over the years through the Beck’s Practical Farm Research (PFR) program, there is a 4-step process specifically for managing weeds in soybeans.
Step 1: Starting Clean
This seems like pretty common sense. Just before we get those beans planted or shortly after those beans are planted, we want to make sure that we get all the weeds that are out there field so that we have a nice clean field to start the season. In a no-till or a minimum-tillage environment, this will require a solid burndown program. In most cases it’s going to be glyphosate plus pick-your-chemical to help assist with broadleaves — so 2,4-D, dicamba, Sharpen, any of those are good options. Obviously, you need to pick that depending on what your soybean herbicide trait is and the variety of beans. There are also options that don’t involve glyphosate. If you want to use Gramoxone, that could be another option to help get that that nice, clean field to start with.
If you’re relying on tillage to tear out your weeds and give you that nice clean start, it’s very important to make sure that the weeds are actually being uprooted. Take the time as you’re setting your tillage tool and deciding what depth to run. Take a walk out behind that tool and just pull up on some of those weeds laying on the surface and make sure that the roots are actually torn up.
Step 2: Pre-Emerge
Applying a pre-emerge with three modes of action is what we found to be most successful in our PFR studies. When we’ve applied pre-emerge residuals with one mode of action, we get about 60% control of waterhemp. When we evaluate it about 45 days after it was sprayed, two modes of action bumped us up to 89% and three modes of action gives us 97% control of waterhemp 45 days after treatment was made. When we get those three modes of action out there, we have the best chance of stopping weeds from emerging. The easiest weed to keep out of the field is one that never grows.
There are four primary groups of pre-emerge herbicides that provide you with residual weed control. Group 2, or your ALS inhibitors, Group 5 our photosystem II inhibitors, Group 14 are PPO inhibitors, and then Group 15 are long-chain fatty acid inhibitors. If you have XtendFlex soybeans, you can use Group 4, which would be your synthetic auxins or dicamba. That counts as well. If you’re using dicamba to burndown, it does have some residual control and can be a great choice.
With the PPO inhibitors, if you have cold, wet conditions at soybean emergence, it might slow those beans down. The beans might look kind of tough, but with more favorable weather, they can come out of that. If that’s a problem you deal with, pick from the three other groups. From those four, potentially five, different herbicide groups as far as mode of action, pick three of those to help keep that field clean.
Step 3: Post-Pass
With post-emergent herbicides, spray by the calendar as opposed to by what the weeds look like. Waiting until there is a weedy mess in the field is waiting too long. Those pre-emerge herbicides provide 3 to 4 weeks of protection. We want to be targeting that post- spray 3 to 4 weeks later. You might struggle from the sprayer to see many weeds out in the field, but we want to get that out there a little bit earlier and target weeds that are 6 inches or less. It’s far easier to kill smaller weeds successfully. It’s also a good idea to get this done before those beans canopy for better coverage of the weeds that are small and down below the soybeans. This also helps get the Step 4 herbicide down to the soil surface.
As far as post- herbicide options go, whether you’re using the XtendFlex system or an Enlist herbicide system, I still really like Liberty as your primary post- option. Liberty and clethodim get your volunteer corn. Liberty and Roundup can do very well also if you have some weeds that are getting bigger. Liberty and Enlist is a great program to help take down weeds that got too large. Maybe it was too wet to get across timely with the sprayer.
I’m a big fan of the Liberty herbicide post- because we’re adding in an additional mode of action. We’ve already used 2,4-D or dicamba in our pre-emerge and when we come back and post- spray, it’s nice to use something different. Liberty is something we’re pretty much only going to use post- on beans and that’s really the only time in our herbicide program we might use that. Anything we can do to mix up those modes of action is going to keep these herbicides working effectively much longer.
Another reason it is important to post- spray by the calendar specifically deals with waterhemp. A large waterhemp plant about a week after it was sprayed looks like it’s brown and dead. The problem with waterhemp is that it has a lot of nodes down near the bottom of the plant and if the beans get too large and the weed gets too large, you’re not going to get good coverage of those lower leaves. The waterhemp will shoot new leaves out of those lower nodes if we didn’t entirely kill the plant, so it’s really important to get those weeds while they’re small.
Step 4: Residual Herbicide
If we’re spraying by the calendar 3 to 4 weeks after applying residual and we’re spraying before the beans are canopied, the fear might be that we’re leaving a window open for more weeds to emerge. Using an in-season residual — adding it to that Liberty and clethodim or Liberty and Roundup or Liberty and Enlist pass — that comes in contact with the soil can help to stop any further emergence of any new weeds until the soybean canopy is closed. That will then give us control the rest of the season. Groups 2 and 15 can usually be applied post-emergence on soybeans with very minimal crop response. Group 15 products tend to be better on smaller seeded broadleaves like waterhemp. FirstRate is a Group 2, but then Dual, Warrant and Zidua are all Group 15s that can work very well and usually have minimal crop response when they are applied late. In our PFR testing, we’ve seen that when we add that in-season residual, we go from 88% control of waterhemp at harvest time up to 94% control of waterhemp harvest. That’s about a 6% increase, which might not seem like much until you think about what that 6% increase in control is really worth. Our PFR team did the math and found that a 6% increase in control results in 17.1 million fewer viable waterhemp seeds per acre in the field for next year’s seed bank. This in-season residual not only keeps our field clean for this year, but also helps to reduce our seed bank for the future.
