Reader question: Late weed applications on stagey canola

June 27, 2019 – Issue 13

Question: I have a field that is fairly dirty with kochia, cleavers and lamb’s-quarters. Half of the field is in 6-leaf and half is staring to bud. How much yield will I lose by spraying 0.5 litre of glyphosate on it?

Answer: Yield loss from late glyphosate applications can range from minimal to significant. A crop that already has some stress (dry, wet, heat, etc.) will often have higher losses. Information from Monsanto, that we included in previous Canola Watch articles, says late application of glyphosate on standard Genuity glyphosate-tolerant canola can cause a 3 bu./ac. yield loss. In some cases, applications at early bud can cause a 20% yield reduction.

On timing. With stagey crops, the 6-leaf close of the glyphosate application window can be an average, with some consideration for where most of the yield will come from — the later-stage plants or the up-and-coming earlier stage plants. However a crop with some plants at 6-leaf and some plants pre-bud will be past stage, on average, and off label. Read more about late applications for herbicides in all HT canola systems.

On weeds. If the kochia, cleavers and lamb’s-quarters are small and behind the crop, the grower may choose to leave them and plan on doing extra weed control in the fall. If the weeds are small and average crop stage is around the close of the window, reduce the amount of glyphosate the canola has to metabolize and spray as soon as possible. This will prevent them from setting seed. Other considerations: Is the kochia glyphosate resistant? If cleavers are the biggest concern, consider using quinclorac alone. Note that its crop stage window also closes at the 6-leaf stage.

Further reading:

Canola Watch