Cutting herbicide rates spells trouble long-term

No. 1: Lambsquarters

The escalation in the cost of crop inputs, including glyphosate and glufosinate, has some farmers looking for ways to save money. Some farmers have asked if trimming back herbicide rates is a viable option.

Going in with a half rate might seem like a good idea, but in the long run it can be a perfect set up for disaster.

“This is a big no-no,” says Jeremy Boychyn, agronomy research extension specialist at Alberta Wheat and Barley. “To me, this is something that although we’re trying to find ways of reducing costs this year, it’s just going to end up being something that may cost us more in the future.”

The recommended rate is recommended because it’s been proven to work in ideal conditions and using the correct spray volume. Deviation from the rate can result in reduced control, crop damage, or worse, resistance.

“We’re talking about a potential increase of resistance development when we start doing half-rates, because that plant can then kind of look to defend itself against that active ingredient, create a bit of systemic resistance, metabolic resistance, and then increase the chance of full resistance occurring later,” says Boychyn.

Peter “Wheat Pete” Johnson, resident agronomist with RealAgriculture, says just don’t do it.

“Typically, the glyphosate recommendation is for 0.7 L per acre of a high-load 540 gram per litre glyphosate. And most growers, when glyphosate wasn’t expensive, would immediately bump that up to a litre,” he explains.

“They may back off to the actual label rate, but even there they really will start to give up  some control on things like sow thistle, Canada thistle,  those tough-to-control perennials, we actually probably need to go to the upper end of the label rate, which is 1.34 instead of 0.72, depends on which product you’re talking about.”

If the rate is backed off to just 0.7 litres per acre, which is the low label rate, the annual weeds will still be controlled, but going below that, weeds like lamb’s quarters will likely get missed, he says.

Johnson explains that the hairs on a lamb’s quarter leaf exude calcium, the droplets will roll right off the leaf, and you’re actually promoting resistance if you go below label rate. Multiple modes of action and full rates are key to avoid herbicide resistance.

“My answer is 100 per cent do not [cut herbicide rates],” says Johnson.

At this point you might be asking: not even if it’s just for one year?

Johnson says that many of these chemistries are overused already and there’s already resistant weeds out there. So “just for one year” if you skimp on the rate and let those weeds get that jump, you’re going to have that resistance issue or an elevated weed seed bank problem that much sooner.

“I think even for one year, you’re opening yourself up for a lot of grief moving forward,” says Johnson.

Check out the full RealAg Radio episode here!

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