A reminder to watch for glyphosate resistant kochia was issued last week to southern Alberta farmers.
Resistant weeds were found last fall near Warner, Alta., and Agriculture Canada researchers Bob Blackshaw and Hugh Beckie have trials underway to assess the ability of 24 tank mixes at various rates to kill the troublesome weed.
Those at the Farming Smarter field school July 11 were reminded of the problem and quizzed on their kochia knowledge by general manager Ken Coles.
“In order to really be able to manage this problem, we have to look at the biology of this plant,” he said.
The annual weed is among the first to emerge in spring, is saline and drought tolerant and can produce 15,000 to 25,000 seeds per year that it can spread at maturity when it tumbles with the wind. It can also outcross through pollen spread.
Coles said farmers tend to spray fields just after seeding with fairly low herbicide rates. By that time, kochia can be well established and is even more difficult to control as the plants mature.
“Really small kochia is really easy to kill. The other problem with it, though, is when they’re small, they’re harder to hit.”
Low drift nozzles with bigger droplet sizes can miss kochia, allowing it to thrive in the crop. The weed also has multiple flushes, so killing older plants can open the canopy and allow younger ones to grow.
Fortunately, kochia seeds are not viable beyond two years, and 70 to 80 percent of seeds will germinate in the first year. That means a short-term perennial rotation or some other means of keeping fields clean for two seasons could eliminate the problem on a localized level, Coles said.
After harvest, he suggested farmers check their fields for kochia and treat or mow before they set seed.
The weed is a formidable adversary, Coles added.
“It’s the earliest up, earliest germinating weed. It’s drought tolerant, it’s saline tolerant, it’s got the best water use efficiency.”
Kochia can send a taproot five metres into the soil to find moisture, making it extremely competitive with crops in dry conditions.
Coles said Beckie and Blackshaw have yet to report interim results from their trials, but it appears herbicide tank mixes containing dicamba are effective against glyphosate resistant kochia.
Even high rates of glyphosate can kill the plants, though that carries the risk of masking the problem so farmers don’t know they are harbouring the resistant weeds.
“While higher rates can help in the management, we could also be making the problem potentially worse.”
At southern Alberta meetings held in March, Beckie said it is too late to contain glyphosate resistant kochia, but they can control its spread.
That will require the use of herbicides with different modes of action, planting competitive crops and using tillage, crop rotation and higher seeding rates.
A website at www.weedtool.com allows farmers to gauge their risk of herbicide resistant weeds.