Skip the Glyphosate Burndown and You Could Lose 11% Yield in No-till Soybeans

An 11% yield loss was observed in glyphosate tolerant soybeans when the first glyphosate application was delayed from pre-planting until the cotyledon to unifoliate stage in 2008 University of Guelph research trials (See Table 1). These results demonstrate that fields with a lot of weeds emerging before the crop will significantly reduce yield if not controlled prior to crop emergence.

* An in-crop glyphosate application was made to both treatments at the 1st to 2nd trifoliate stage
**95% confidence that the application of a burndown treatment resulted in this yield benefit
*** The application of a burndown in Woodstock did not significantly impact soybean yield.

Residual herbicides "buy time"

Once the crop is up, it should be kept weed-free from the 1st to 3rd trifoliate stage to minimize yield losses from weed competition. If you have fields with heavy weed pressure, adding a residual herbicide to the pre-plant burndown appears to mitigate the risk of yield loss that comes from delayed in-crop glyphosate applications due to unsuitable weather conditions. At the Elora Research Station in 2008, a 10 day delay in the in-crop application caused a 5 bu/ac reduction in yield. This reduction in yield was eliminated when a residual herbicide was added to the pre-plant glyphosate treatment.

NS = Yields not significantly different then the treatment consisting of a glyphosate burndown followed by an in-crop glyphosate application at the 1-2 trifoliate stage.
S = Yield significantly higher then the treatment consisting of a glyphosate burndown followed by an in-crop glyphosate application at the 2-3 trifoliate stage.