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How Early Can You Spray Roundup Ready Soybeans?

It’s safe to apply glyphosate to Roundup Ready soybeans as early as the late cotyledon stage when the first unifoliate starts to appear, says Bruce Brolley, Manitoba Agriculture, Food and Rural Initiative’s (MAFRI) pulse crop specialist.

Warm weather over the weekend gave weeds a jump on slowly emerging soybeans. With rain in this week’s forecast, farmers want to spray their soybeans as soon as possible, Brolley said Monday.

When applying Monsanto’s most concentrated glyphosate, WeatherMax (540 grams of glyphosate per litre), farmers can safely apply 0.3 to 0.5 litres per acre, Brolley said.

While it’s safe to go as high as 0.6 litres an acre, weeds are small now and should be easily controlled at lower rates, Brolley said.

Farmers who want to control volunteer Roundup Ready canola right now should apply a Group 2 herbicide and not a contact weed killer such as Reflex.

It’s safer to apply contact herbicides later when the soybeans are bigger, but such uses are not registered currently and therefore illegal. [email protected]

About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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