Resist: spray between the rows

Like the plague, herbicide resistance is spreading to more chemistries, more crops and more fields. There’s no magical new herbicide over the horizon to conquer this scourge upon the land.

Researchers around the globe are fiercely focused on finding ways to break the hold herbicide resistance has on the world’s farmers. But, with no chemical angel winging her way in to save the day, farmers and researchers agree that a temporary solution likely rests in finding new ways to use tools already at our disposal.

“How ‘bout figuring out a way to spray between the rows without hitting the crop. Maybe use some sort of shroud?”

A farmer mentioned that idea to University of Saskatchewan researcher Chris Willenborg a couple years ago. The more Willenborg thought about it, the more it made sense, until last year when he decided the idea was ready for the U of S fabrication shop.

Saskatchewan farmers have all the herbicide resistance problems experienced in Manitoba and Alberta, plus with a large lentil acreage, they have a double dose of trouble. Lentils have given growers a good cash crop, but herbicide resistance has been significantly eating into their bottom lines.

Over the years, wild mustard has become resistant to Group 2 herbicides. Lentil growers have no firm solution, so Willenborg decided there was nothing to lose in trying the shrouded nozzle idea.

Willenborg said spraying wild mustard between the rows might also allow application later in the season, thus curtailing the spread of resistance.

The shrouded nozzle study Willenborg and his team did in 2018 was only on lentils. However, he says the technology holds promise for all types of cereal, oils seed and specialty crops. Also, the lentil plots had been planted on very narrow ten-inch spacing. Wider spacing would make it easier to control the chemical application.

“Steve (Shirtliffe) and Eric (Johnson) will be starting some work in wheat and barley, and I’m looking at expending the project to cereals as well this summer,” says Willenborg.

“To be honest, we haven’t perfected it yet. It’s kind of a novel concept. We just built it in the last year or two, so there’s still some kinks to be worked out. The hard-ware came from a company called Garford Manufacturing in England. They also offer a guidance system using digital cameras, like they use for inter-row tillage. But we didn’t buy that. For our small plot work, guidance is provided by the driver.

“But for a grower here in western Canada, I think RTK can guide the sprayer with enough accuracy that you’d keep the product off the crop.”

Willenborg says lentil crops grown in an inter-crop regime aren’t hit as badly by wild mustard. But there are lentil fields impacted every year by Group 2 and Group 9 resistant kochia and Group 2 resistant wild mustard. He says there are not many products on the market that can deal with these situations.

This is the view from a weed’s perspective as the shrouded sprayer passes over with a fresh dose of glyphosate. The plastic shroud allows a non-selective herbicide to be applied between crop rows. In initial trials last summer at the University of Saskatchewan, the shrouded nozzles successfully sprayed between them. | Chris Willenborg photo

The research included a comparison between glyphosate and selective herbicides applied with the shroud. He said there was some minor crop damage when a bit of glyphosate snuck around the shroud and got on the crop.

“A side benefit of the shroud system just spraying be-tween rows is that it greatly reduces the amount of glyphosate applied to each field. I’d like to see this technology coupled with our existing in-row herbicides. You’d have one set of nozzles spraying selective herbicides directly on the crop, along with a set of shrouded nozzles spraying glyphosate between the crop rows. So you’d have lots of different modes of action. And then you’d drag a weed wick on top of that to catch weeds taller than the crop canopy.

“There are all kinds of things we can do with this idea, not only to kill weeds this year, but also to break herbicide resistance. Right now we think of a sprayer as just having a single toolbar. Given the size of booms and high level of technology employed by these companies, I think it’s viable to see multiple toolbars on a sprayer.

“The best time to stop herbicide resistance is before you have it, and you do that with multiple modes of action, timing and selective application. I’m hopeful manufacturers will take this project on and build field-scale shroud sprayers.”

The spray shroud lets you apply different chemicals side-by-side, in-crop an inch apart. You can apply glyphosate between rows while applying a cocktail of lethal selective herbicides on the crop.

The obvious benefit is a cleaner field. In the long-term, this strategy of tank mixing selective herbicides to spray on the crop can remove more herbicide resistant weeds from the total population. The proliferation of herbicide resistant weeds is at least delayed, according to agricultural application expert Tom Wolf.

“It allows you to invest in more effective tank mixes. If you’re only spraying half the area, then you can afford to spend more on the tank mix,” Wolf said.

“We know the method called multiple effective modes of action is effective, but right now the cost of a mix prevents most farmers from using it. Depending on your row spacing, you might cut the cost of product in half using a spray shroud. That means you can actually double the amount you invest in your multiple mode of action tank mix.

“For example, we know kochia is resistant to glyphosate and the Group 2 mode of action. So to control kochia you need at least two different modes of action that are not Group 2 or Group 9. Not just one different mode of action, but you must have two. Every single weed must be hit by at least two modes of action that can control it. That’s what we call multiple effective modes of action.”

Unfortunately, even this measure will not eliminate herbicide resistance. Wolf says it will only delay the on-set because we are still fostering the same selection process that caused the problem in the first place. Eventually the weeds will develop resistance to all the chemical tools now available to farmers. In the U.S. corn growers regularly fight invasive weed species like palmer amaranth, which is resistant to seven modes of action.

Wolf says some states have adapted a war on weeds campaign called Start Clean, Stay Clean. It’s much like Alberta’s war on rats. It promotes the idea of totally weed free fields.

“Ohio now has a saying ‘Let no pig weed survive’ to express their total control of weeds. They simply do not want any resistant seeds to remain viable and re-produce. It might be impossible, but they are working hard at it.

“It flies in the face of some IPM (integrated pest management) studies we’ve been asked to adapt in the past. For instance we’ve been talking about thresholds. Below a certain weed count there’s no yield loss, so you don’t bother to spray. You just let them go. Now there’s this shift in thinking with their Start Clean, Stay Clean campaign. Now they say in Ohio let no weed survive.

“But let’s remember that herbicide resistance on the Canadian prairies is a result of that same philosophy of promoting totally clean fields. Totally clean fields are achieved by over-use of chemicals.”

He cautions that if we ever get new modes of action, we must be careful not to abuse them the way we did with Group 2 and Group 9 chemistries. Farmers and re-searchers agree that what’s really needed is a new mode of action.

You might have to wait 10 years, but there are at least a couple in the pipeline. The Philadelphia-based chemical company is working with two molecules not related to existing modes of action. Their immediate goal is to tune them for corn and soybeans. It has proven to be effective on Palmer amaranth. The first launch is expected by 2026.They say the discoveries are significant because they mark not only a new active ingredient, but a new mode of action as well.

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