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New Killer For Kochia In Flax

Western Canadian flax growers have a powerful new herbicide to control Group 2-resistant kochia, called Authority.

But there’s lots for farmers to consider before using Nufarm’s new pre-emergence product with residual weed control. Soil pH, organic matter and texture will affect the application rate and in some cases prevent its use.

And there are re-cropping restrictions, including a 24-month wait from the time Authority has been applied in a field before canola can be seeded.

“It (Authority) will be a really good addition to our arsenal for controlling weeds in flax,” Anastasia Kubinec, Manitoba Agriculture, Food and Rural Initiatives’ oilseed specialist, told farmers here March 3 at the Manitoba Flax Growers Association’s annual meeting.

“This is a chemical that’s very powerful and you need to know what’s going on in your soil,” she said.

“I do recommend soil testing and finding out what the organic matter is and the pH and figuring out what the soil type is.”


Authority’s active ingredient is sulfentrazone. It’s also registered for use in sunflowers and field peas. In addition to kochia it controls red root pigweed, wild buckwheat and lamb’s quarters.

Authority was registered in 2009 for use in chickpeas in Saskatchewan.

The higher the soil pH, the more Authority is available to control weeds but the chance of crop increases too. As a result Authority is not recommended in soils with pH levels exceeding 7.8. The same holds in sandy textured soils.

The flipside is the lower the soil pH, the less Authority is available and weed control can suffer. The same is true in soils with high organic matter. Authority isn’t recommended in soils where organic matter exceeds six per cent, Kubinec said.

“I can’t emphasize this enough, you’ve got to soil test, you’ve got to know your farm as far as what your organic matter is, soil texture and critically what your pH is,” said Nufarm’s Manitoba sales manager Myles Robinson. “Those things will determine the rate you use.”

Most Manitoba farmers will apply one jug of Authority to treat 40 acres, Robinson said.


Farmers will get the best results from Authority if they seed first and then apply the herbicide, but they must do so within three days or risk injuring the newly geminating crop.

Farmers can also apply Authority and then seed, but where the soil is disturbed weeds could escape the herbicide.

“Anything we can do to minimize that soil disruption will be good for weed control,” Robinson said.

Unlike older pre-emergent herbicides, Authority shouldn’t be worked after it has been applied.

“The worst thing you can do is go over it with the harrows,” he said.

However, Authority does require a quarter-to a half-inch of rain to activate it.

Authority will work in fields with lots of crop residue so long as it’s evenly distributed and there’s rain to wash the herbicide into the soil, Robinson said.

It’s important to work down soil clumps too before applying Authority because they can contain weed seeds, he said.

The goal is to get the herbicide evenly spread across the field and then washed into the soil forming an even layer. The newly germinating susceptible weeds die after coming in contact with the herbicide, which inhibits an enzyme critical to photosynthesis.

Robinson recommends applying Authority with 10 gallons of water per acre to get the best coverage.

“Ten gallons (of water) covers a lot of mistakes,” he said.


Although Authority, a Group 14 herbicide, is registered in Canada to control just four weeds at a suggested retail price of $15.30 to $19 an acre, it does control a number of others.

Authority is registered in the United States as Spartan and has more weeds on its label. Nufarm focused on four weeds to speed up the registration process.

“I’m going to go out on a limb and say if it (sulfentrazone) controls cleavers in North Dakota there’s a damn good chance it will control cleavers in Manitoba,” Robinson said.

Meanwhile, Nufarm is working to add more weeds to Authority’s label.

It’s also investigating whether the recropping intervals can be shortened on some crops. Currently, oats can’t be planted following Authority for 36 months.

Flax growers that use Authority this spring can plant wheat, corn, barley, alfalfa and sunflowers in 2012. Farmers would have to wait until 2012 to plant canola.

Nufarm is also looking into getting Authority registered for use in soybeans and edible beans.

Authority will not kill any weed that’s already present above ground, Robinson said. That’s why farmers should consider a pre-seeding burn-off.

“We are very comfortable with tank mixing it (Authority) with our glyphosate Credit and our new and improved burn-off product CleanStart,” he said.

Authority is very effective on kochia. In independent, replicated plots it was found to control the weed 100 per cent after 77 days. In fact, Authority is so effective on kochia, Nufarm wants farmers to use the herbicide in the same field only once every four years.

“If something controls kochia at the 100 per cent level we’re really selecting for kochia plants that are more tolerant,” he said.

“We want to manage this and avoid building up resistance.”

Authority is not registered for fall application and should not be applied by air.

Authority shouldn’t be left over night in a sprayer tank because it will thicken requiring a lot of agitation before it can be sprayed again.

Sunflowers are a little more suscept ible to injury and should be planted one inch to 1.25 inches deep.

Authority will also magnify damage to sunflowers planted in fields with residual Group 2 herbicides present.

Farmers unsure whether Authority is right for their fields should contact Nufarm or their local pesticide retailer. [email protected]




About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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