Weeds that emerge before or with the crop will have the biggest impact on yield potential. These need to be controlled as they will outcompete the crop for soil nutrients, moisture and sunlight. Dandelions and quackgrass tend to be the most common and most competitive perennial weeds to emerge before the crop. Pre-seed burndown is ideal for these weeds. Narrow-leaved hawk’s-beard is also much easier to control early with a burnoff. Control after hawk’s-beard starts to stretch upward is much more difficult.
If the burnoff didn’t get done or missed these weeds, then control has to be early in the life of the crop to prevent significant yield loss and, in the case of quackgrass in particular, contain a tank mix with good activity on grasses.
Canada thistle tends to be later emerging than dandelion and quackgrass, but Canada thistle can be tough to control with straight glyphosate early in the year. That’s because right now all energy movement within the plant is to foliar top-growth and out to the leaves. Glyphosate will stay in the top of the plant, and may kill a few leaves, but not the whole plant. In response, the Canada thistle will often set more shoots off the roots, to compensate. Lontrel is about the only choice for early season thistle management in canola.
What does the 6-leaf stage look like? Basically, you want to make sure canola plants do NOT have flower primordial growth, which puts it outside of the foliar stages and into the reproductive stages even though it may still be in a rosette.