Weed competition: The second application

June 15, 2016 - Issue 13

Growers who usually spray twice may not need that second pass this year if the canopy has closed, weeds are behind the crop, and the recommended application window is past. The crop should out-compete the weeds all on its own, and the economic benefit of the second herbicide application just won’t be there.

For perennial weeds that have escaped but are delayed relative to the crop, growers may consider pre- or post-harvest glyphosate application as an alternative, especially if the weeds are delayed enough to avoid seed set prior to swathing.

Some canola fields face intense competition from grassy weeds this year.

Some canola fields face intense competition this year.

A second in-crop spray only makes sense…

…If growers use canola as a clean-up crop for Group-1 resistant wild oats, narrow-leaved hawk’s beard, round-leaved mallow and other tough weeds, a second herbicide application may be required to do the job.

…If weeds are plentiful, at the same stage or ahead of the crop and the canopy hasn’t closed, these weeds may have a large yield impact. Note however that you’re still required to follow label rate directions even if these large weeds might require a higher rate for control. A pre-harvest product is another option to consider.

…If weeds are at levels too low to influence yield, but are potential grade impacting weeds — such as cleavers — a second spray may pay off if it can do a job on these weeds.

Another option, if you still haven’t made the first pass, is to use a higher registered rate the first time around.

Further reading:

Liberty performance in cloudy conditions. Liberty generally works best in bright sunshine and when temperatures are warm, but consider the upcoming forecast and how long you could potentially be waiting for an “ideal” day. Timing often trumps efficacy.
Weed control when wet
Aerial options for weed control
Podcast on spraying tips
Late herbicide applications
Grassy weed control in canola

Canola Watch