Glacier FarmMedia — It makes some intuitive sense: stimulate weeds’ growth at the wrong time of the year and let the winter frost kill them off. The challenge, says a scientist, is finding the right stimulant to wake them up.
Shaun Sharpe, a weed researcher with Agriculture and Agri-Food Canada (AAFC) in Saskatoon, may have discovered the right substance to accomplish this: wood vinegar, otherwise known as pyroligneous acid or liquid smoke.
Although the results of the 2021 greenhouse study were moderate (wild oat emergence was around 10 per cent greater than wood vinegar compared to the untreated control), it’s given Sharpe a greater confidence in both the compound’s potential and the prospect of waking weeds up just in time for Mother Nature to kill them.
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“These experiments kind of confirm that wood vinegar is active and it is able to stimulate germination and emergence of wild oat. And it’s able to act on a process that keeps them dormant. And it’ll work effectively after the seed has been produced.”
Attempts to use wood vinegar as a biostimulant aren’t new, Sharpe says. The research dates back to the 1980s but has been largely lost in limbo since then, at least on the Prairies.
“With the onset of a lot of our herbicides coming to market this kind of experimentation stopped because of how effective those herbicides were. So I’m pulling back an old idea to see if it’s going to be able to be used in our production systems now.”
Wood vinegar — generally known to the public as a flavouring agent, under the title “liquid smoke” — is a byproduct of making biochar. It’s been known to break seed dormancy in many plant species.
Potassium nitrate (KNO3) was also tested as a stimulant because it’s widely available to producers, Sharpe says.
The study was conducted at AAFC’s Saskatoon Research and Development Centre. Its objective was to measure the ability of the two agents to stimulate germination and emergence in target plants, including wild oat and volunteer wheat, volunteer barley and oat.
“We did some work in petri dishes with seeds directly. And then we also did some work in pots in an incubator to try spraying through a conventional sprayer…so that it would be a spray pattern akin to how a producer would do it,” Sharpe says.
The compounds were placed with the seed in the petri dishes while — for the potted work — seeds were deposited in the soil and sprayed with KNO3 or wild vinegar at 200 litres per hectare.
As it turned out, all the species in the petri dishes germinated with KNO3, but there was no stimulation to increase germination — although higher doses promoted inhibition.
Plants sprayed with KNO3 in the pots saw some emergence — but again, there was no stimulation for further growth.
Sharpe said other, similar studies have seen a stimulating effect from KNO3 but it tends to be inconsistent. In this study there also appeared to be a resistance issue.
“I think what happened here is these wild oats we were using were already adapted to its stimulation and it wasn’t effective anymore. So it’s maybe not a reliable option for a producer to try to stimulate that weed out of the soil.”
The petri dish experiments with wood vinegar saw no germination at all unless the researchers used very low doses (less than one per cent) on wild oat. “It was only with the wood vinegar when sprayed on pots where we saw any stimulation to promote their emergence,” said Sharpe.
Those wild oats were sprayed with wood vinegar at 200 litres per hectare.
The pot side of the research on wood vinegar was divided into two separate treatments. One increased emergence by about 10 or 11 per cent compared to the untreated control using 50 and 100 per cent solutions of wood vinegar.
The second treatment also saw emergence grow by 11 per cent using a 10 per cent solution.
The pots and petri dishes were well-watered, creating an ideal condition for them to grow. The results have caused Sharpe to wonder if there would have been a greater effect if water was more limiting.
“That’s kind of an area I want to touch on as we go forward,” he says.
And Sharpe is going forward. He hopes to test wood vinegar in the field, in the process observing whether it can control weeds post-emergence.
“So it could have a dual use pattern where when the plants are emerged, it can potentially be used as a herbicide to burn that.”
