Using Acetic Acid to Control Weeds in Organic Potatoes

Organic Agriculture Centre of Canada

Researchers on Prince Edward Island are reporting encouraging results in using a key ingredient in vinegar to control weeds in potato crops.

The active ingredient in vinegar is acetic acid, a natural chemical and therefore a potential organic alternative to synthetic herbicides.

Household vinegar usually contains about 5% acetic acid, but this wasn’t strong enough to control weeds, says Jerry Ivany, lead author of the study.

The challenge for researchers was to determine the most effective concentration of acetic acid that would control weeds but not cause significant crop damage. Application timing was also critical.

So researchers experimented with three concentrations, 10, 20 and 30%, applied at different stages of plant growth. After two years of study, Ivany found encouraging preliminary results, reported in “Acetic acid for weed control in potato (Solanum tuberosum L.)” published in the Canadian Journal of Plant Science.

The most effective concentration was 20%, applied in a 30-centimetre band over the potato row, at 300 litres per hectare. Acetic acid applied in the early stages of weed leaf growth – and before the potato leaves emerged – resulted in control similar to the synthetic herbicide metribuzin. Weeds between the rows were removed by mechanical cultivation.

Six weeks after treatment, the acetic acid controlled 86% of lamb’s-quarters and 96% of corn spurry, only slightly less effective than metribuzin at 100% control. When it came to wild buckwheat, the acetic acid resulted in 93% control, topping metribuzin at 80%. 

Timing is particularly important since potato plants from tubers usually take 10 to 14 days for leaves to emerge. The broad-leaf weeds being targeted develop faster, so there’s an opportunity to control weeds with acetic acid without damaging the potato plant.

“If you can get it on before the crop emerges … you can get weed control and not injure the crop,” said Ivany in a telephone interview.

Potatoes are produced in all provinces of Canada and in recent years organic potato production has increased. In 2004, 938 hectares of organic potatoes were produced in Canada.

Though the focus of the research was on potatoes, the results could be similar for other crops. Each crop, however, has to be approached individually and different growth stages need to be considered.

“You have to work those things back and forth to find out where your zone is … that gives you the time of application, stage of crop and rate,” said Ivany. “You have to look at the whole thing.”

These same considerations apply to organic and conventional farmers. Ivany said both types of farmers could benefit from the research. If a treatment using acetic acid costs less than a synthetic herbicide and can provide comparable weed control, farmers will save money.

Organic farmers traditionally have had fewer options. Most weed control has been mechanical. “You’re looking at cultivation, time of cultivation and land preparation to control weeds.”

Ivany said the idea for researching the effectiveness of acetic acid came from the considerable amount of literature available on the use of vinegar in weed control. “The chemical we were looking at is a natural product.”

The next step was to refine the concept to find products that met Canadian Organic Standards, which specify what can or cannot be used in an organic crop.

Vinegar would be acceptable and the initial research has shown there is good potential for acetic acid to be used as a weed control agent in potato production.

Yet more research is needed to get a product onto the farmer’s field.

Since a chemical is involved, “growers cannot make use of it legally” until the product is registered with Health Canada. All products for use on crop production in Canada have to be registered under the Pest Control Products Act.

This registering process, usually undertaken by a private company, requires considerable support information and studies and can take several years to complete. The registration must specify the intended use, which weeds it controls, rates and concentration of the product and other information.

Ivany said the process may be slow, but it’s essential since “it’s done for the safety” of food.

This article was written by Steve Harder on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the Organic Federation of Canada and industry partners
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Posted December 2010