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Dicamba drift a new danger for potato growers

Glyphosate has always been an issue, but new Xtend soybeans will likely see more dicamba applied

Crop damage caused by herbicide drift should be a risk on Manitoba potato producers’ radar this year.

Soybean producers are gearing up to plant Roundup Ready 2 Xtend soybeans following European Union approval last summer. The soybeans are tolerant to both glyphosate and dicamba herbicides.

Andy Robinson, potato agronomist with North Dakota State University.
photo: Supplied

But dicamba drift can cause irreparable damage in neighbouring potato crops, said Andy Robinson, a North Dakota State University extension potato specialist, during a presentation on herbicide drift at this year’s Manitoba Potato Production Days.

“Potatoes are sensitive to many herbicides,” said Robinson.

Exposure can result from soil carry-over, particle drift, contamination of spraying equipment, volatilization, misapplication and spot spraying.

Particle drift is a common culprit. Robinson pointed to research showing particles sized five microns in diameter can travel laterally up to three miles, compared with larger droplets sized 400 to 1,000 microns in diameter, which can travel around 8.5 to 4.7 feet respectively.

The new dicamba technology is a big deal for soybean producers, said Robinson, but it carries the risk of drift or off-site movement.

“We want producers to understand the ramifications on off-target movement of herbicides,” said Robinson in an interview.

Potato plants injured by dicamba spray exhibit epinasty, stem twisting and leaf cupping and stem swelling and elongation, while tubers are malformed.

Robinson has completed a study looking at the impacts of dicamba and glyphosate residues on potato. Data will be included in a forthcoming publication, but the study showed that exposure to the two herbicides reduced marketable yield and size over multiple years.

“These herbicides are not friendly to potato,” said Robinson.

Preventive measures

There are steps potato producers can take to protect their crops from dicamba exposure. The first is to talk to neighbours and alert them of the size and location of potato fields.

“Talk to your neighbours and let them know that potatoes are sensitive to dicamba so they can be aware of that when spraying,” said Robinson. “Any time spray drift happens it’s not good for anybody.”

If producers are spraying other crops than potatoes, they should maintain a dedicated potato sprayer. Producers who outsource spraying should have a conversation with custom applicators to make sure they are cleaning their tanks.

Physical barriers can be employed via crop borders or buffer zones. Producers can put out signs around potato fields indicating that the crop is sensitive to herbicide drift.

“Train employees about herbicide problems, and scout regularly, especially walking field edges,” said Robinson.

Ultimately, the responsibility for containing spray drift lies with the applicator. “Whoever is spraying, it’s ultimately their responsibility to keep everything within the field,” he said. “If you’re a soybean grower you don’t want to drift onto a potato field because the cost of potatoes is so much higher.”

Robinson said that in the U.S., some label provisions stipulate applicators can’t spray dicamba if there are specialty crops downwind, including potatoes.

Monsanto Canada’s weed management technical lead Joe Vink says the Canadian label for the company’s dicamba formulation, XtendiMax with VaporGrip Technology, stipulates several application requirements to prevent off-target effects. For example, producers can only use spray nozzles that produce ‘extremely coarse’ to ‘ultra-coarse’ spray quality, should set boom height to no more than 50 cm above target, and should avoid spraying during temperature inversions.

“I think in general there is opportunity for more awareness and understanding of what temperature inversions are, what to look out for to not spray in them – sudden drop in wind speed and clear evening when the sun is going down, how they impact pesticide applications and how they can significantly contribute to off-target movement with dicamba,” said Vink.

He adds that soybean growers do not have an obligation to spray dicamba if the herbicide is the wrong fit for an area, as the new varieties are also tolerant to glyphosate and other burn-down products in the Roundup Ready system.

“There is no obligation to spray dicamba in Roundup Ready 2 Xtend soybean that is beside a potato field – this is an application choice that can be made,” he said.

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