Control the Weed Seed for Cleaner Fields

Consistent, on-time application of residual herbicides cleans fields and protects yields.
Control the Weed Seed for Cleaner Fields
A tractor sprays a residual herbicide on a soybean field in spring. Overlapping residual herbicides with at least two effective sites of action applied at full labeled rates is key to managing weeds and minimizing the soil’s weed seed bank.
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Weeds will run roughshod over crop fields if given the chance — and they get that chance every year. Getting a jump on the soil’s weed seed bank with a clear weed management strategy is key to higher yields and maximized profits at harvest, according to T.J. Binns, agronomic service representative for Syngenta.
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“There’s a lot of planning that goes into managing weeds, and a lot more that should go into it, as opposed to what we’re doing a lot of times,” he says. “A proactive approach is much more successful than a reactive approach.”

Staying Ahead of Weeds

Bill Johnson, Ph.D., professor of weed science at Purdue University, says getting a jump on weeds is the only hope a farmer has of really controlling them, especially considering the speed with which they can become resistant.

Weeds are present on every acre every year, and they’re easily the most detrimental factor in terms of yield loss of any of the pests that we have out there.

Bill Johnson, Ph.D.
Professor of Weed Science
Purdue University
“Weeds are present on every acre every year, and they’re easily the most detrimental factor in terms of yield loss of any of the pests that we have out there,” he says.

Over the last 20 years or so, the effectiveness of Roundup® herbicide on big weeds taught growers to wait until weeds are well out of the ground to go after them, Johnson says. That bad habit led to greater weed pressure and increased the number of weed populations that are resistant to the chemical. The only way to stop that trend is to target growth stages to increase the length of time that herbicides are effective.

Both Binns and Johnson agree that overlapping residual herbicides with at least two effective sites of action applied at full labeled rates are key to managing weeds and minimizing the soil’s weed seed bank. To maximize herbicide effectiveness, growers must target small weeds.

“The thing we really try to get growers to understand is that a weed is most vulnerable to anything you do to it right after it’s germinated,” Johnson says, “so that’s when we want to target our control efforts.”

By overlapping preemergent and post-emergent applications of residual herbicides, growers can greatly reduce the chance of leaving missed weeds, or escapes, in the field. That’s important because weeds grow quickly. For example, Binns says a four- or five-day delay in treating Palmer amaranth could mean 5-inch-tall weeds that are much harder to manage.

“It’s easier to control a seed than a weed,” Binns says. “So just missing the window and delaying that application can take you from a proactive approach to a reactive approach.”

Finding Out the Hard Way

Doyle Jost, a Kansas farmer who grows corn, soybeans and wheat, has been there.

“We learned the hard way when Roundup quit killing things like it was supposed to,” Jost says. “There was a year or two there when we were kind of behind the eight ball, trying to figure out what we were going to do, just throwing everything at it.”

Eventually, Jost connected with J.J. Voth, agronomist at Ag Service, Inc., in Hillsboro, Kansas, to come up with a solution. For corn, Acuron® corn herbicide from Syngenta was an obvious choice, with its four active ingredients — mesotrione, S-metolachlor, atrazine and the novel chemistry bicyclopyrone — delivering a higher level of weed control and outyielding competitive herbicides by 5 to 15 bushels an acre.* They’ve since tailored Jost’s program using Acuron’s sister product, Acuron Flexi, which includes mesotrione, S-metolachlor and bicyclopyrone, while customizing the atrazine level in the tank.

“We can basically add as much atrazine as we need to, or we can split up the rate of atrazine for the season,” Voth explains. “Like the name says — it gives us more flexibility.”

Protecting Soybeans

For burndown plus residual, Jost uses BroadAxe® XC herbicide on his dicamba-tolerant soybeans, with glyphosate or another broadleaf weed herbicide at planting. BroadAxe XC delivers excellent residual control of weeds, including the more evasive species, such as Russian thistle, morningglory and kochia.

“BroadAxe XC is what we recommend to growers for their main residual program at planting time,” Voth says.

At the Jost farm, they follow BroadAxe XC with Prefix® herbicide as the post-emergent residual, plus tank-mixed dicamba and glyphosate partners. The two effective sites of action in Prefix provide five weeks of residual activity to inhibit weed emergence and growth while preserving available sites of action to prevent multistacked resistance.

Another option for dicamba-resistant beans is following BroadAxe XC or Prefix with Tavium® Plus VaporGrip® Technology herbicide, a premix of dicamba and S-metolachlor that controls both preemergent and post-emergent weeds for up to three weeks longer than dicamba alone. With the U.S. Environmental Protection Agency’s recent decision to extend the registration of Tavium on dicamba-tolerant soybeans and cotton, growers will have access to this valuable chemistry in 2021.

Johnson, Binns and Voth all agree that keeping long-term results and the soil’s weed seed bank in mind should be top priorities when planning a weed management program. They’ve also seen what happens when growers look at weed control as a place to cut costs. It’s a false economy that can have repercussions for years, Voth says.

“Over time, if we’re increasing that weed seed bank in the field, it’s just going to be that much more expensive to control the weeds down the road,” he says. “When weeds go to seed, we have to deal with those seeds for however many years they’re viable in the soil. It’s not just a one-year thing.”

Unsettled markets can bring on what Binns calls emotional decision-making, which often leads to shortsighted choices. Cutting rates or products or abandoning a plan that’s been working in favor of one that costs less but ultimately doesn’t get the job done can come back to bite a grower at harvest time.

“They think they’re saving money; but by the time they do reactive applications to clean up what the other stuff missed, they’ve actually spent more money on herbicides and didn’t raise as much yield to go along with it,” he says. “They take a double hit.”

*Acuron yield advantage range based on 2016 Syngenta and university trials comparing Acuron to Corvus®, Resicore®, SureStart® II and Verdict® applied preemergence at full labeled rates. For more information on Acuron versus an individual product, ask your Syngenta representative.