A full, labeled rate — in conjunction with timing — is one of the most important things a grower can do to implement an herbicide program that successfully keeps rows clean, maximizes yields, and prevents weeds from developing resistance.
The application rate is especially vital to address in an era when farm finances are tight and corn producers feel pressured to find new ways to cut costs. Misguided money-saving strategies have trended toward using cheaper herbicides or cutting application rates, both of which can have long-term ramifications for the growing season and the sustainability of the land.
Industry insiders note that these approaches can be partly borne out of past experience and the difficulty growers have in understanding how the landscape has changed. For example, a farmer may have been successful using a lower corn herbicide rate just five or 10 years ago, but it’s very likely that their weed populations back then were lower or their herbicides appeared more efficacious because the most troublesome weeds hadn’t yet entered their fields.
A full, labeled rate, when applied at the right time, is an important step for growers aiming to maintain clean rows, improve yield results, and prevent weeds from emerging.
“No skimping on weed control because uncontrolled weeds will produce seeds. And if you don’t control them well, let them drop the seeds, you’re going to fight them at least three to five years later,” said Dr. Stevan Knezevic, with the University of Nebraska-Lincoln Department of Agronomy and Horticulture. “I would not recommend to cut the rates.”
There are multiple reasons that cutting herbicide rates is a bad idea, and in all instances, there are no financial long-term benefits that make it worth using only a partial rate.
For starters, using a full, labeled corn herbicide rate means that the grower gets the complete duration of residual activity, which for many products is four to six weeks, while for the newest technology, like Storen™ herbicide from Syngenta, that can be as long as nine weeks.1
Knezevic, whose research includes data analysis of critical weed-control periods, also stated that reducing the label rate means that growers run the risk of not killing the weed and could inadvertently spur a population shift toward hardier weed species or biotypes.
“You are crippling [the weed]. And for lack of a better term, you have only partial control, and those plants can survive,” he explained.
Every time a weed is able to grow after an herbicide is applied, herbicide-resistant offspring become a possibility. The industry saw that to full effect with glyphosate, which was used for many years at all kinds of different rates. The emergence of resistant weeds was the unfortunate outcome.
Shawn Hock, Syngenta Product Lead for Corn Herbicides, said that when he gets contacted by a grower who is unsatisfied with weed-control performance, one of the questions he asks is, “What rate were you using?”
It’s so simple, yet it’s foundational to understanding where the shortfalls are in a weed management program.
“That’s often one of the first things I’ve got to overcome with growers, to show them that using a full, labeled rate will get that weed control they want,” Hock said. “Every year is different, too. In some years, a two-thirds rate could look like a full rate in the field, but in a harder year, that’s not the case. Because you don’t know what kind of year you’re going to have before you plant your crop or spray your herbicide, the real ticket is to use a full rate up front for the best results.”
The active ingredients in Storen are bicyclopyrone for burndown and residual control of broadleaf weeds and annual grasses in corn, mesotrione for burndown and residual control of broadleaf weeds, S-metolachlor for residual control of annual grasses and small-seeded broadleaf weeds, and pyroxasulfone for residual control of annual grasses and broadleaf weeds.
“When you put four of the best residual active ingredients together that control resistance-prone weeds, it’s no wonder that we are seeing a higher level of control with Storen, when used at a full labeled rate, than any other product. It was by far the most impressive residual herbicide in our corn herbicide trials,” said Brett Miller, Regional Head of Field Development for Syngenta Crop Protection.
Which leads into the other major reason for full, labeled corn herbicide rates: yield optimization.
Heavier rates of a modern pre-emergence such as Storen are showing impressive benefits for yield, explained Chris Munsterman, Agronomic Service Representative with Syngenta. Trials point to a 4 to 5 bu/A yield advantage2 for corn growers using Storen, which was tested in areas where notorious Palmer amaranth and waterhemp are especially challenging.
“If you just use a tiny little bit there, it doesn’t add any herbicide benefit whatsoever, other than exposing the weeds to a sub-lethal rate, which actually selects for resistance,” Munsterman said.
Additionally, Palmer and waterhemp are dioecious species, which means there are male and female plants. So, when pollination occurs between separate male and female plants, a hybridization occurs that makes these plants conducive to developing resistance.
To help address issues like this, Munsterman said he and his colleagues talk a lot about overlapping residuals. Where Storen, for instance, would be a 2.4-quart use-rate per season, Munsterman said he often recommends going 1.6 quarts in the first pass at planting and then coming back in 21 days later with 0.8 quarts to overlap that residual and recharge the herbicide rate in the soil.
In areas where Palmer is overactive, the weeds easily metabolize post-emergent herbicides — they “just eat them up like Pac-Man,” Munsterman illustrates. By the time weeds get some size to them, they become wildly more difficult to control. Stopping weeds before they start means that there is less competition for water, nitrogen, light, space, and other resources as the corn plant grows.
“There is about a 2 percent yield penalty for every corn leaf stage of delayed control,” Knezevic said.
A full-rate herbicide application keeps weeds from even coming up in the first place and allows crops to canopy more quickly.
“You want an herbicide that’s going to work in every field in every growing season,” Hock said.
And in a biological weed network where resistance is the dominant gene and easily transferred to offspring, it becomes increasingly vital to use full, labeled corn herbicide rates that prevent resistance from multiplying on the farm for years to come.
This article was published on behalf of Syngenta. Visit this page to find a Syngenta Crop Protection Specialist near you.
Ryan Tipps is the founder and managing editor of AGDAILY. He has covered farming since 2011, and his writing has been honored by state- and national-level agricultural organizations.
