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Evaluating mechanical weed control options

Researchers found that when two methods are used, weed control improves

With the rise of herbicide resistant weeds, researchers at the University of Saskatchewan are looking into alternative weed control methods focused on in-crop mechanical tools to give growers new management options.

Why it matters: Farmers are looking for alternative solutions to deal with herbicide resistant weeds that are becoming tougher to control and are affecting yields. At the same time, societal pressure against traditional crop protection product use is increasing.

In-crop harrowing, using a minimum-till rotary hoe and inter-row cultivation are three methods that graduate student Alexander Alba evaluated as part of a study led by Steve Shirtliffe of the department of plant science at the University of Saskatchewan.

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The rotary hoe was shown to work well, controlling pre-emergence or newly emerged weeds, with excellent crop tolerance at any growth stage. In-crop harrowing was used at the three-node stage, but it damaged the crop. It also doesn’t work well in low-till, high residue situations, according to Shirtliffe.

“One issue we have with the harrow is that in high-residue situations where we aren’t tilling much, a harrow can’t be used. It gets plugged up, like trying to run a regular comb through Bob Marley’s hair,” Shirtliffe told the audience at the annual Canadian Weed Science Society conference recently in Niagara Falls.

“The tolerance of the rotary hoe was good though, although they don’t like rocks and rocks don’t like them.”

Steve Shirtliffe spoke at the recent Canadian Weed Society conference.
photo: Lilian Schaer

Once the crop rows were visible, inter-row cultivation was used to manage weeds, which Shirtliffe said was “pretty good” if it was used early in the critical period, but that it could impact yield if used later on. Unfortunately, this method only worked for weeds growing between the rows and not in the actual rows themselves, limiting its effectiveness.

Overall, all three methods provided weed control and reduced weed biomass, but Alba also compared all three methods to each other to answer the burning question, which one is best?

Using two mechanical weed control methods provided better results than only using one, increasing crop yield by about 70 per cent and reducing weed biomass by about 80 per cent. The combination rotary hoe and inter-row tillage proved to offer the most consistent control.

According to Shirtliffe, doubling the seeding rate could also be an option for some crops.

In research conducted with lentils, for example, doubling the seeding rate resulted in a 16 per cent weed biomass reduction and a 30 per cent yield boost.

When mechanical weed control was added, the weed biomass decrease fell to 76 per cent and yield increased 55 per cent.

Minimizing seed production in weeds is another mechanical control alternative. Many weeds produce their seeds above the crop canopy, so clipping the weed canopy, which is used in organic production, could prevent that weed seed production.

One such tool is the CTM weed surfer from the United Kingdom, where it is used primarily by organic producers for above-canopy weed cutting, Shirtliffe said.

Alternatively, Sweden’s CombCut cuts weeds below the canopy top, using a comb-like system that cuts coarse weed plants near the ground but lets thinner crop plants slide through unharmed. Shirtliffe has conducted some research using this tool in lentils to deal with herbicide resistant wild mustard.

“If we did it weekly, there was no viable mustard seed left and it didn’t affect the lentil crop yield at all,” he said, adding that they had less success managing wild mustard this way in cereal crops.

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