Dicamba Update: Strong in the Residual Game

CropLife had the opportunity to speak with Dr. Brandon Schrage, Technical Service Manager, FMC Agricultural Solutions, at Commodity Classic about his observations on the inherent troubles with dicamba and the company’s approach to resistance prevention.


Dicamba Update: Strong in the Residual Game

CL: How do you approach the issue of preventing dicamba-resistant weeds?

When you think about dicamba, we’ve had it for some time. What’s interesting about the issue of resistance with dicamba vs. glyphosate, is glyphosate was largely neglect – it was the industry’s fault. We were over-relying on it; it worked so well, we were cutting rates. What’s different with dicamba now, is we have a system where there are so many restrictions.

Whether it’s a downwind buffer that now doesn’t get treated, or if we have off-target movement, those are areas where we’d see sublethal rates get applied to various weed species. Sublethal rates leads to that selection pressure for resistance. It’s different with dicamba, because we’ve used so much of it in the past, whether it be Status or different burndown options. I think the resistance is going to come on stronger than glyphosate did.

Dr. Norsworthy out of the University of Arkansas did some work where he looked at three generations of sublethal rates, and we had a fully dicamba-resistant Palmer amaranth plant. It’s not going to take us long to get there, if we’re not using all the tools we have.

I don’t care whether we’re using crop rotation or cover crops, even using tillage in certain situations, because the seed of a lot of amaranthus species doesn’t have much longevity in the soil. I know a lot of folks right now are no-till now for soil health benefits, but we need to use all the tools we’ve got. If you look at the overreaching data and how we can economically control weeds, it still relies on synthetic herbicides. At FMC, we’re strong in that residual game. Any university researcher in the country would tell you, start clean, stay clean. Use fall residual options, use an effective preemergent, overlay those residuals, and then come in with an effective post.

When we consider parts of the country that are targeting Palmer amaranth, that’s where a lot of the attention goes, for the post-emergent products or even the pres. But in the western Corn Belt where kochia is a problem, or areas like Michigan or Ohio where they have a lot of ragweed species that emerge early, starting in the fall is a good idea. Throw in 12 or 14 oz. of Authority MTZ, that right off the bat gets us a PPO and a PS2 inhibitor to get us through the spring. In certain situations, we might not be able to get a pre down. It’s wet, and sometimes we struggle to plant. If we can get an effective pre down, at that point we can go with a sulfentrazone product like Authority Supreme, which includes pyroxasulfone, which is a Group 15. Now, before you’ve even got a crop out of the ground, you’re looking at three modes of action. We have a lot of options and are not tied to any one seed package.

I think the science speaks for itself: if we don’t start aggressive with those full labeled rates, with preemergent herbicides, then we’re just asking for trouble down the road.

CL: How much are you seeing people practicing these methods, now three years in, to try not to have a repeat?

It’s a good question, and it’s hard to quantify. In some areas, folks are really good, because they learned the hard way from the glyphosate resistance and ALS. They are being proactive. We have a lot of guys in the Corn Belt using fall-applied residual programs. Purdue University put out an excellent publication that testifies to that.

Palmer amaranth can emerge in the fall, and still go to seed. It doesn’t need many growing degree days to make that happen. So immediately after harvest, we have to start thinking about weed control for the next year. We really have to have a zero-tolerance policy of escapes. The foundation for that, the initial success, is found in preemergence herbicides. That’s where FMC puts a lot of stock in our residual portfolio.

CL: Beyond residuals, there are other elements that have come to light over the past couple of seasons that could play a role in leading to resistance early, such as the pH level issue.

The restrictions are kind of asking for resistance. Let’s say I have my mandatory 57-foot buffer. Now I have a part of that field that’s not getting treated. They’ll come back with a pre and other postemergence options, but if we have glyphosate resistance or the weeds get too tall for Liberty, usually on those field edges is where we’re seeing a lot of escapes. The dicamba system itself is asking for trouble in some respects.

When you add that to the research shown – that when you add glyphosate it becomes more acidic, dissociates the salt, and we get greater volatility – that’s a problem. The weed control with Roundup is really good; you pick up grasses and other weeds, so it’s more option-limited.

Dicamba is nothing new. We just have never seen it applied in this volume at this time of year.

CL: The percentage of dicamba acres this year is also expected to be way up, to more than 60 million acres of Xtend soybeans and XtendFlex cotton.

It’s massive. And it’s sad that a lot of growers are choosing to adopt the dicamba-tolerant soybeans just so they’re not worried (about drift.) In many cases, these drift concerns are not going to lead to a yield loss. A lot of folks are OK even though they may not think they are.

Years down the road, I’m sure we’re going to have another really great post herbicide option. As these new ones like Enlist come out, the easiest time to control weeds is when they are small. That’s even before they get out of the ground, when they’re imbibing water, when they’re first getting ready to germinate. That’s when you start to see (the best control.)

CL: Do you have a sense of how much the Enlist system will compete?

It’s hard to say. You figure, we already have 2,4-D resistance in waterhemp and other species. It’s going to be spooky. Using every tool we can is the trick.

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