"If you want to maximize canola returns next year, start right now by doing a good job of post harvest weed control," says Christine Mardell, Canola Council of Canada agronomist for the Peace River Region.

If weeds are not managed after harvest there is still time for seed set which will increase the weed seed population. Mustard and most annual grasses are finished setting seed by the time swathing begins. However, green foxtail, buckwheat and perennial weeds (such as Canada thistle) will continue to set seed after harvest until a killing frost.

In addition to setting seed, weeds continue to consume large amounts of water after harvest. This may have a serious impact on available moisture the following spring, especially if snowfall is in short supply this winter.

"Fall weed control dramatically reduces weed competition in the spring crop, and allows the grower to wait until annual weeds emerge before spraying. But managing weeds in the fall is not an easy task. Weeds can be fairly large and may be difficult to control with herbicides. However, a glyphosate application can still be effective if the weeds (particularly dandelion and Canada thistle) are still actively growing and the leaves have not been damaged by fall frost," Mardell says.

Winter annuals (henbit, stork's-bill, chickweed, cleavers) can also be controlled with an application of 2,4-D. Leaving these weeds until spring allows them to get a jump on the growing season. "By the time the soil dries enough for a spring herbicide application, it's often too late since these weeds will be too big to control," she points out.

Winter annuals including cleavers, stinkweed and shepherd's purse are "canola unfriendly" broadleaf weeds because they either have no control methods in conventional canola or are expensive to control in the crop. Fall control of these weeds is a good option.

Good fall weed control is equally important for herbicide-tolerant and conventional canola.

Mardell says if using herbicides for post-harvest weed control, keep in mind that the amount of chaff and dust covering the weeds can limit herbicide efficacy. If trash is covering weeds, she recommends harrowing before spraying. She adds that fall tillage will give 80 to 90% control of fall-germinated weeds, including larger, earlier germinated weeds. In addition, tillage brings annual weed seeds to the surface, allowing them to germinate and a fall frost to kill them. Leave canola seeds on or near the soil surface as long as possible after harvest. Many of the seeds left on the soil surface will germinate and be killed by fall frost. Canola seeds that fail to germinate in the fall can be controlled with spring tillage, pre-plant herbicides or post-emerge herbicides, she says.

For more information in your area, contact:

John Mayko, Agronomic Research & Extension Manager, 780-764-2593 Derwyn Hammond, Manitoba, 204-729-9011 Jim Bessel, North Central & North Eastern Saskatchewan, 306-373-6771 David Vanthuyne, Eastern Saskatchewan, 306-782-7799 David Blais - Western Saskatchewan, 306-895-2122 Christine Mardell, Peace, 780-518-1513 Doug Moisey, Central Alberta, 780-645-3624 Nancy Muchka-Dahl, Southern Alberta, 403-625-0510


This press release is part of the Canola Council's Canola Advantage program. The program is supported regionally by: Alberta Canola Producers Commission; Saskatchewan Canola Development Commission; Manitoba Canola Growers Association; Canola Council of Canada; Peace River Agriculture Development Fund; and B.C. Ministry of Agriculture, Food and Fisheries.