How late can you spray?

Many growers have not been able to apply their second and some cases first weed control application but the crop is near the end of the application window. Roundup can be applied up to the 6-leaf stage, Liberty up to early bolting, and Odyssey up to 6-leaf stage.

The question at late-application stages is whether weed control trumps crop damage. Spraying when the earliest plants are at the bud stage or beyond can sometimes lead to bud blasting, pod blanking, as well as delayed maturity and stunted height for those earliest plants, particularly if the plants are already suffering from other stress.

And it may already be too late to prevent yield losses from weed competition. “By the time the crop reaches the point where it is beyond the tolerance of the herbicide, most of the yield damage has already been done and any weed control is now directed at managing harvest,” says Clark Brenzil, weed control specialist with Saskatchewan Ministry of Agriculture.

The key is to accurately assess crop staging. While some plants may be bolting, at what stage is the bulk of the crop? That is what you use to make weed control decisions and to assess yield potential.