The Reality of Managing Weeds in ’22
September 28, 2022 Despite abundant preparations for the 2022 season to stay ahead of supply shortages, soaring input costs, and ultimately, weeds, uncooperative weather demonstrates again that nothing comes easy in farming.
Where it was dry — the Western plains — it was very dry, and that lack of activating rainfall often impeded the performance of preemergent herbicides, resulting in large weeds and a scenario where the slightest variations in weather, herbicides, nozzles, spray volumes, and adjuvant selection mattered. At times, growers cut rates to save money or were dealing with herbicides with which they weren’t as familiar, because they couldn’t secure supply of their top choices.
“It could have been a few days’ separation between having a very successful postemergent season and one that they weren’t satisfied with,” Shawn Hock, Corn Herbicides Product Lead, Syngenta, told CropLife® magazine.
Hock said Syngenta focused on helping growers and ag retailers maintain balance in their fight against high costs and supply challenges while keeping resistance management strategies top of mind and dynamic. “Using sound resistance management strategies while also making a financial gain are behind our messaging, ‘better yield is the better deal,’” he said. “That’s one of the struggles many of us have, is we want to do the right thing and delay resistance, but there’s also a yearly financial risk we’re trying to manage as well from an operational perspective, such as being able to address weather, volatility, and rising land and input costs.”
For example, the company shows that use of its Acuron corn herbicide can give growers a 5- to 15-bushel yield advantage while supporting resistance management with its four sites of action that are also effective from a residual standpoint and reduce weed competition, because weeds don’t just take up space above ground, they also eat up valuable fertilizer and water underground. “We’ve been able to show a $24 per acre cost from allowing 2- to 4-inch weeds to consume fertilizer nutrients. Three-inch-tall weeds in three days can use an inch of water,” he added.
High Pressure On Post
In Ohio, high input costs drove many to skip residual herbicide applications entirely, according to Mark Loux, Professor of Weed Science and Extension Specialist at The Ohio State University. On the whole, growers’ ability to manage weeds is “the best it’s going to be” with the still-new 2,4-D and dicamba technologies before those start to break, he said. While resistant waterhemp is grabbing most of the attention in the state, common ragweed resistance is on the rise though more isolated, he said.
“One of the results of resistance is you run out of residual herbicides that have activity on beans, so it throws it all back on the post. That’s increasing,” he said. In Ohio, dicamba was used less this year postemergence, because major distributors simply refused to spray it in such a congested state, and that has put even more pressure on Liberty, he said.
In walking fields recently south of I-74 in Illinois and Indiana, Nick Hustedde, Technical Support Representative at FMC, noticed that when folks sprayed postemergent technologies in soybeans, weeds frequently towered above four inches.
“The foliar herbicides would inhibit terminal growth, but we would notice regrowth below that, and it would trigger another post application to try to clean those up. The more this occurs, the more likely we are going to select for resistance,” he explained.
One of the key learnings for FMC customers and through the research it implemented this year, is the importance of applying residual preemergent chemistries somewhere close to planting and making a sequential early postemergence application with residual activity. “Instead of waiting for the weeds to trigger a post application in terms of height, we need to get a sequential application on the calendar approximately 18 days after they plant the crop,” he advised.
While the best way to curb metabolic resistance is to not expose these weed populations to post herbicides, he recognized that the reality is that it’s not possible. “We’re going to have to spray waterhemp and palmer and other weeds postemergence,” he said. “When we do, it will be imperative to optimize every post application by using the right rate, selecting the right carrier volume, making sure sprayers are calibrated right, using the right adjuvants, and considering some of the environmental parameters that can influence efficacy — like temperature when we’re treating, relative humidity, sunlight intensity, time of day, and the forecast. There may be a choice day where we can optimize more of these postemergence chemistries by getting across more acres on that specific day.”
For as heavy as the discussion is around weed resistance, in his area, pockets of resistance are still isolated and management is doable, so he avoids doom-and-gloom talk with growers. “As you drive across my territory and throughout the Midwest and Mid-South, there are still a lot of really clean fields out there,” Hustedde said.
The mindset of using residual chemistry as the primary weed control mechanism and post applications as a secondary or last resort will help growers, as well as thinking about options that aren’t poured out of a jug. “We don’t want to deter benefits that we’ve seen out of conservation tillage and soil management,” he said. “If you’ve got a field that’s flat and has high pigweed density, it may make sense to implement an aggressive tillage pass. Row spacing is another one that’s low-hanging fruit — if we can narrow our rows down from 30s to 15 or 15 to drilled row spacing, there will be quicker canopy.”
More cover crop utilization, especially cereal rye, to minimize weed pressure in the spring was also more prevalent this year, according to several people with whom we spoke.
From Brookings, SD, down through mid-Iowa, where Kyle Gustafson was driving, scoping out fields when we spoke in early August, he took note of cleaner bean fields from a year ago.
“This year, our waterhemp control has been better than it’s been in the past,” Gustafson, Crop Protection Product Manager with WinField United said, while he also noticed poorer grass control and more volunteer corn, as he suspected that people traded out pricey glyphosate for less effective clethodim-type products.
“I wonder if a lot of growers and retailers had the mindset of, we don’t have a lot of herbicide inventory, and we might have only one chance to make some of these herbicide programs work,” he said. “If it doesn’t work, it may be hard to respray because we may not have the supply. I wonder if that played in their minds, that we need to make sure the weeds are smaller, have the right adjuvants and water volume and amount of herbicides. That’s one thing I’ve noticed this year, is more people doing the little things right.”
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