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Growers considering a pre-harvest glyphosate cannot apply it to canola (RR or non-RR) until seed moisture drops to 30% or lower. This roughly coincides with 30% seed colour change. Spraying earlier raises the potential for glyphosate residue in seed. Pre-harvest glyphosate will kill green weeds and even out the crop for straight combining, but it can take up to 3 weeks to do its job under cool fall conditions.
But what if the grower hasn’t sprayed at all? Some growers fighting excess moisture are still trying to get their first glyphosate application on their Roundup Ready canola. They’ll now have to wait until after seed has less than 30% moisture — for the reasons stated above.
Glyphosate is not a desiccant. Glyphosate will even out the crop and allow weeds to die and dry naturally for easier straight combining, but it will not make the crop mature faster. Premature application of glyphosate will simply increase the risk of excess residues, which could impact acceptability of the crop in foreign markets, and terminate seed filling prematurely, resulting in shrunken seeds with higher green count. Click here for more on pre-harvest herbicide.
Cleavers. Some growers in eastern Saskatchewan who didn’t get a chance to spray through the growing season because of excess moisture are seeing very large cleavers poking up through the canopy. Pre-harvest glyphosate may stop a small proportion of seeds from reaching maturity, but many of the seeds are likely already mature enough to remain viable. Unfortunately it is likely too late to avoid issues with cleavers seeds in dockage or back on the ground after harvest.