Weeds: When would a second in-crop application make sense?

June 10, 2015 - Issue 13

A second application of in-crop herbicide is not always economical if the crop is well established, competitive and ahead of the remaining weed population. However, a second application can make sense…

—If growers use canola as a clean up crop for Group-1 or -2 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 above the economic threshold of the crop, and at the same stage or ahead of the crop, these weeds are likely to have a large yield impact. Keep applications within the rates and stages indicated on the herbicide labels. Failure to do so can result in yield losses and jeopardize crop sales. A pre-harvest product is another option to consider when the in-crop window is missed.

—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.

Note that once canola is past the 6-leaf stage the majority of yield loss from weed competition has already occurred. Herbicide application provides little yield benefit.

Canola Watch