Considering Chemical Applications to Assist Crop Dry-Down?

Growers who have decided to straight combine some of their canola may be considering pre-harvest weed control or desiccation, particularly in fields with uneven or late maturity. While these products can hasten dry down of mature plants, they will kill any immature ones. It is also important to understand that these products are not designed to seal the pods against pod shattering, and in some cases may make the crop more vulnerable to shattering if harvest is delayed. Be prepared to harvest as soon as the crop is ready, because the more rapid dry down will leave the crop vulnerable to shattering sooner than if it is left to mature on its own. If applying pre-harvest chemicals with ground rig sprayers, crop dividers can reduce the amount of crop loss due to trampling and shattering. In addition, traveling back and forth in the direction of prevailing crop lean will help reduce losses.


On Roundup Ready canola varieties, a pre-harvest glyphosate application will assist in some dry down of green weeds and offer perennial weed control, but it will not dry down the crop. For other types of canola, it is critical not to apply the product too early. Apply when the crop has 30% or less seed moisture content. At this stage, which is past the typical swathing timing, pods are green to yellow, and most seeds have turned from green to yellow or brown. For a faster acting desiccant like Reglone, it is even more important to delay application to allow seeds to reach physiological maturity. The recommended stage is when an average of 60-75% of seed on the whole plant has turned brown. Keep in mind that this will be well past 75% seed colour change on the main stem.


Also use only products that are registered for pre-harvest application. The use of unregistered products may leave unacceptable levels of residue in the seed.


Post-harvest weed control may be an option this year due to the good growing conditions this fall without frost. Post-harvest weed control will help maximize canola returns next year by controlling hard to kill weeds such as dandelions at a time when translocation to the roots (and hence herbicide efficacy) will be maximized. Post-harvest is also a good time to control winter annuals such as stinkweed, cleavers or shepherd’s purse or perennials such as Canada thistle. Managing weeds after harvest will help limit weed seed populations in the following years. A few tips for maximizing post-harvest weed control are:
–  cut stubble high to leave as much plant material as possible,
–  spread straw and chaff adequately to leave plants exposed and
–  spray when new plant growth is evident or when leaves are present.

More information on fall weed control is available at the following link: