Kochia continues to be difficult for producers to manage

Charles Geddes’s spouse knows the demands of travelling with a weed ecologist. This summer, he tasked her with taking photos of kochia from a moving car as Geddes drove prairie highways and byways.

Unfortunately, there was plenty of kochia to photograph, Geddes told those at the Jan. 15 Agronomy Update in Lethbridge. As an Agriculture Canada researcher in weed ecology and cropping systems, Geddes is studying kochia’s biotypes, distribution and management.

The herbicide-resistant weed continues to expand its territory, aided by its ability to tumble in prairie winds and drop copious amounts of seed.

There was a lot of it in the past growing season because kochia thrives in dry conditions, and some of the remaining chemical tools available to fight it are not as effective in dry conditions, Geddes said.

Management is further complicated by the fact that herbicide-resistant kochia tends to germinate later than other kochia and may have a prolonged germination period. Agriculture Canada weed scientist Hugh Beckie, who has done extensive work on herbicide resistance, has shown that in his research.

“So we’re seeing these resistant populations actually emerging and developing later in the growing season compared to susceptible populations,” said Geddes.

“There’s a greater potential to miss these seedlings … with a pre-seed herbicide application.”

If growers scout for kochia only in the most productive areas of a field, they may miss plants in saline or other low-lying areas that delay their emergence.

Geddes said kochia seed reaches 50 percent viability in about 200 days. However, a small amount of seed can still persist for a long time, possibly up to three years. Even if one percent of the seed on one kochia plant survives in the seed bank, that’s still 300 seeds. Kochia can produce 30,000 seeds per plant per year.

Many farmers harvest around patches of kochia still green in the fall to avoid plugging harvest equipment. Then they manage those patches when time permits.

Geddes said that might be unwise given that researchers don’t yet know when kochia seed becomes viable. If it is cut after seed viability, farmers risk spreading it further.

The point of seed viability is one focus of his research. He is also testing pre- and post-harvest herbicides, the effect of crop rotation on the weeds and the effect of higher seeding rates and different row spacings.

“It’s just like adding another mode of action,” Geddes said about cultural weed controls.

“We are now seeing very limited options as far as herbicides specifically for in-crop herbicide application,” he said.

“We’re really not going to be able to spray our way out of this problem.”

In Alberta, a 2017 survey showed about half the kochia population was resistant to glyphosate, compared to only five percent in 2012.

All Alberta kochia populations are now considered resistant to Group 2 herbicides with about 10 percent also resistant to Group 4 and Group 9.

Saskatchewan is doing a survey this year using a 2013 survey as a base line. In Manitoba, results from a 2018 study have yet to be distributed. Geddes said most of the resistant kochia shows up in glyphosate-resistant corn and soybeans. That’s a contrast to Alberta’s situation, where the pesky weed was first found in chem-fallow fields.

Prairie farmers can submit kochia for free diagnostic testing, said Geddes. The Prairie Wide Diagnostic Testing Service will analyze plants for resistance to glyphosate, dicamba and fluroxypyr.

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