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Glyphosate drives long-term herbicide changes

Ontario keeps track of detailed herbicide use every five years, which shows how the use of active ingredient has declined

A study of glyphosate use in Ontario shows the herbicide has created significant change in crop management.

It shows that while corn and soybean acreage and yield have increased in the province since 1983, the impact of herbicide use per acre has declined, in large part because glyphosate has displaced other herbicide chemistries.

Why it matters: Glyphosate has had a rough ride lately, partly because it is used on so many acres, but also because a jury in California recently awarded a man damages after he attributed his cancer to the use of glyphosate in his work. Government data, like this from Ontario, is important for farmers who continue to assert that glyphosate is safe and beneficial.

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Chris Dufault, an agrologist and former head of re-evaluation and use analysis section of the Pest Management Regularly Agency (PMRA) and Rob Saik, founder of Agri-Trend and principal of Saik Management Group, looked at data from the Ontario Ministry of Agriculture, Food and Rural Affairs, which they say is useful because is it collected every five years using the same method, and has been since 1983, so it will show trends over time.

The most-recent survey was from 2013-14.

Glyphosate’s popularity skyrocketed because it is effective on both broadleafs and grasses and can be sprayed on corn and soybeans modified to resist the herbicide. That simplified weed control for many farmers, but recently it has also resulted in greater concern with weeds resistant to the herbicide.

However, there can be no denying the effect of glyphosate on herbicide application in Ontario. Between 1983 and 2013, the total amount of herbicides applied to fields declined by 39 per cent. The reduction is due to the fact that glyphosate is applied at a lower rate of active ingredient than the herbicides it replaced. Use of glyphosate increased from one per cent to 54 per cent of total herbicide use in that time.

The decline in total herbicide use happened at the same time as an 11 per cent increase in the acres of corn. Yield also increased 74 per cent over that 30-year period.

In soybeans, acreage increased by 188 per cent, while the total herbicide applied to soybeans increased 47 per cent. Dufault and Saik also attribute this to the replacement by glyphosate of herbicides with higher application rates. Soybean yield per acre increased by 53 per cent in that time period as well.

Dufault and Saik also highlighted an Ontario government report that ranked herbicide active ingredients by their Environmental Impact Quotient — an indicator of a pesticide’s ability to do harm.

The EIQ, as calculated using 12 points in the Ontario study, was 15.3 for glyphosate, 10th lowest of the active ingredients evaluated. For example, atrazine has an EIQ of 22.9.

Dufault and Saik say not only has the volume of applied herbicides decreased with glyphosate use, but the toxicity of the herbicide applied has also declined.

National regulators use much more stringent evaluations than the 12 points in the Ontario EIQ. The herbicide has regularly been reapproved by regulators and Dufault and Saik say that is partly because of the larger volume of data country regulators have available to them, compared to other organizations such as the International Agency for Research on Cancer. The World Health Organization body classified cancer as “probably carcinogenic.”

“Glyphosate has played a key role in enabling many farmers to achieve excellent weed control in herbicide-tolerant crops while adopting reduced or zero tillage. This reduction in cultivation has positive implications for the environment in terms of soil health, water holding capacity and greenhouse gas balance,” Default and Saik conclude.

About the author

Editor

John Greig has spent his career in agriculture journalism and communications. He lives on a farm near Ailsa Craig, Ontario. Contact John at [email protected] or follow him on Twitter @jgreig

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