Forget the silver bullet, bring out the arsenal against kochia

Study using multiple methods to control one of the most dangerous weeds on the Prairies

If it’s a one-on-one battle, put your money on kochia.

The pernicious weed is not only a prolific seed producer, thrives in harsh conditions, and spreads its progeny far and wide, it’s also a master when it comes to developing resistance to herbicides. So producers are urged to use a variety of ‘best management practices’ to control kochia before it gets out of control.

But what’s the best recipe?

That’s a question that Farming Smarter is addressing it a four-year study on controlling the weed — a project that is field scale in scope, site specific, and utilizes a bevy of high-tech tools, including satellite and drone imagery and advanced GIS (geographical information systems).

You need an arsenal of weaponry when going up against kochia, said Farming Smarter researcher Lewis Baarda during a field school earlier this month.

Lewis Baarda.
photo: Supplied

“The characteristics of kochia include its rapid seed production,” Baarda said during the digital and in-person event. “It has about 20,000 to 30,000 seeds per plant.”

It also emerges early, does well in saline soils, flourishes during droughts, and spreads its seed over large areas after drying off and becoming a tumbleweed.

But it is the weed’s ability to develop resistance to herbicides that makes it such a huge threat, he noted.

It developed Group 2 herbicide resistance about 30 years ago and about 10 years ago, batches of kochia able to tolerate glyphosate (Group 9) began to show up in the States. Today, kochia is considered to be fully resistant to Group 2 herbicides, and a 2017 survey in southern Alberta found more than 50 per cent of kochia populations were also resistant to glyphosate (a Group 9 herbicide).

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“It’s almost impossible to find a sample of kochia that is not resistant,” said Baarda. “One of our main tools for managing weeds is only 50 per cent effective. That illustrates the need to take a multi-pronged approach to managing kochia.”

And while rotating and mixing herbicides is part of that approach, the chemical solution alone is doomed to fail. The same 2017 survey also found 18 per cent of kochia populations were resistant to Group 4 (dicamba) herbicides. Even more worryingly, 10 per cent of sampled kochia were resistant to all three groups. That number has likely risen since.

“That’s a harbinger of tough times ahead to managing kochia with herbicide options,” said Baarda.

But there are other tools in the toolbox and the Farming Smarter study, which is being conducted on three 160-acre fields, is using a host of them.

When kochia arrives in a field, it usually develops in patches, generally areas where there is low productivity, said Baarda. Limited tillage is one control method but must be done before seeds become viable.

The study is also looking at the effectiveness of combining both crop rotation and chemical rotation.

“You can get a bunch of different crops and different chemical options,” said Baarda. “Different crops have different qualities that might make them more or less competitive with kochia as well.”

Since the weed doesn’t do well when there’s a lot of competition, bumping seeding rates can help.

“When there are risk areas, you can increase seeding rates, and boost seeding rates in areas of the field,” he said.

However, you need to take time ahead of seeding to ensure the seed drill is properly calibrated.

“Any time you have any misses or anything that will germinate a little later, that’s an opportunity for kochia to get up and get established. Just like any weed, the further along it is, the tougher it is, the harder it is to control.”

Another tool is growing salt-tolerant forages that will compete with kochia and hinder its establishment. Cover crops and inter-row cultivations can also be effective tools. Destroying seeds with a Harrington Seed Destructor, or bowing or cutting a plant before it becomes mature, can also work.

The four-year kochia control project is being done in collaboration with Charles Geddes, a research scientist with Agriculture and Agri-Food Canada in Lethbridge. Along with characterizing each field (for salinity, soil factors, nutrients and topography), the researchers are also using precision ag tools. This includes taking aerial images (RGB and infra-red) during the growing season and salinity mapping and then overlaying them using GIS technology.

Farming Smarter has seeded nine crops into nine different stubbles, and is studying the kind of kochia pressure that develops.

Although only in the second year of the project, a couple things have really stood out, said Baarda.

“Following Roundup Ready canola, we had quite a bit of kochia pressure, more than all the other crops,” he said. “That tells you that glyphosate resistance is a big deal, and might have a risk tied to it.”

In fields where peas were grown, they were given a pre-seed application or a fall application of Authority, which is a Group 14 herbicide, which gives residual control.

“Even if you apply it in the fall, it will manage the crop for a while, until the crop gets established,” said Baarda. “Our pea plots looked really good regardless of what stubble they were planted in.”

The corn plots had more kochia because of wider row spacing.

The findings from the study will help growers learn how to control kochia without having to apply herbicides on their entire field, said Baarda.

About the author

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Alexis Kienlen

Alexis Kienlen lives in Edmonton and has been writing for Alberta Farmer since 2008. Originally from Saskatoon, Alexis is also the author of two collections of poetry, a biography, and a novel called "Mad Cow."

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