Forget herbicides. Sandblasting will whack those weeds

Since the dawn of agriculture, farmers and gardeners have been locked in a battle with weeds. The war, which puts more than $528 million in crop losses on the line each year in Canada alone, has for the past 50 years been fought with an arsenal of toxic herbicides that harm human health and contribute to the biodiversity and climate crises.

In this epochal struggle, weed expert Jichul Bae believes farmers could soon have an unconventional weapon at hand: sandblasters packed with corn grits and crushed walnut husks.

On a recent spring day, the Agriculture and Agri-Food Canada researcher joined two colleagues in a sun-baked Fraser Valley blueberry field to test out a new approach to weed management for B.C.'s most valuable crop. The team drove a golf cart-sized tractor equipped with a sandblaster through the rows of blooming shrubs. Every few metres, they blasted patches of grass or horsetail with a high-pressure jet of air filled with ground corn grits or walnut husks.

The idea is to weaken the plants, making them vulnerable to stressors like pests and more susceptible to synthetic herbicides, which, for this experiment, the team used only once and at half the normal rate, Bae said. In contrast, most non-organic commercial growers apply the chemicals three times a year and use about twice as much chemical at each application.

"The eventual goal is to eliminate herbicide application (entirely)," he said.

It is a massive task. According to the United Nations, in 2016, we used roughly 4.1 million tons of all pesticide-active ingredients worldwide, more than double the quantity used in 1990. There is growing evidence many of these chemicals harm the environment and human health, and contribute to farm emissions by degrading carbon-rich soils.

Although most Canadian farmers still use pesticides, many are now finding the chemicals no longer work.

Pesticide-intensive farming practices have fuelled the growth of superweeds resistant to most conventional herbicides. Widespread use puts a "super strong selective pressure" on weeds, killing off all but the most resilient, University of British Columbia professor Julia Kreiner explained in a December interview.

Those that survive pass on the resistance to their offspring, and after a few generations, only the herbicide-resistant plants remain. For some species, that evolution can happen in just three to four years, forcing farmers into an "arms race" between pesticides and plants, Kreiner said.

The problem is particularly severe for B.C. farmers because of their proximity to the U.S. Bae explained that American farmers are allowed to use more pesticides than Canadians, which drives up herbicide resistance on both sides of the border and puts Canadian farmers at a disadvantage. The gap is getting bigger as Canadian federal regulators restrict pesticide use further over its environmental and health risks, Bae added.

American growers also have access to support from specialists who help them find creative solutions to deal with weed problems more effectively than B.C. growers. Bae said he is B.C.’s only independent weed specialist — a position he never expected to be in.

Born in South Korea, he was an avid snowboarder who studied biology at university. He moved to Canada for snow and school, where he researched how to control the common allergen ragweed growing alongside Quebec highway medians. That project led him to weed research and accepting his current position with Agriculture and Agri-Food Canada in B.C.

His job has an aspect he wasn't expecting: In addition to his research, he constantly helps farmers figure out how best to beat back the weeds.

That's where the sandblaster comes in. First developed for cornfields by researchers at the University of Nebraska-Lincoln, Bae thinks the approach could help drastically reduce synthetic herbicide use or make it easier for organic-certified herbicides to be effective. Organic herbicides are natural or biodegradable and, depending on the chemical used, can be less harmful to the environment and health.

The results of Bae's study, now in its second year, show promise, but there is still work to do. Blasting weeds with walnut husks or sand grit and using a small amount of herbicide reduced the size of the weeds by 75 per cent. However, the total number of weeds in the field remained relatively unaffected by the treatment.

"Seventy-five per cent (in biomass reduction) looks amazing, but it should be above 85 or 90 per cent to be effective," he explained. The study will continue through the summer of 2024, offering insight into whether sandblasting weeds works better over several years.

The technique could also have unexpected environmental costs, warned University of British Columbia conservation biology professor Claire Kremen.

Bees and other pollinators rely on a diversity of pollens and nectars to survive. Any techniques that reduce the diversity of plants growing in farm fields are "bad for bees," whether they use herbicides or not, she said in an email.

Moreover, she pointed out that both walnut shells and corn grits come with their own environmental baggage. Many walnut and corn growers use herbicides on their crops, potentially outweighing the benefits farmers can gain from sandblasting. Many types of corn grits are also edible and if they would otherwise be used for food, using them for sandblasting "doesn't make sense."

"This sounds like a minor adjustment to farming practices that will probably not do much to improve the sustainability of agriculture, although possibly it could reduce the use of herbicides in some places (but beware of it being used to create the sandblasting components)," she said. "We need more substantive changes to accomplish agricultural sustainability, especially getting away from highly simplified agricultural systems."

Still, for Bae, the project seems promising enough that he plans to expand the research to look at whether organic pesticides or other types of abrasive materials might work better. He also dreams of building a robot that could roam the rows identifying and sandblasting weeds without human input, saving farmers time and labour.

His work with local farmers has proved rewarding in some unexpected ways. He recalled the first time he attended B.C.'s largest agricultural convention after accepting the Agriculture and Agri-Food Canada job, many farmers were delighted to see the Lower Mainland had a weed expert on hand.

"They treated me like Metallica or something," he said.