Canola School: Managing weeds early in the season


Starting the year off on the right foot requires a little bit of forethought and planning. When it comes to keeping a canola crop clean during the early stages of growth, there are some steps to take before even seeding the crop.

Dr. Charles Geddes, research scientist in weed ecology and cropping systems at Agriculture and Agri-Food Canada in Lethbridge, Alta., joins Kara Oosterhuis for this Canola School episode on early season weed management.

“When we’re talking about early season weed control, one of the first things to consider is scouting,” says Geddes. “Scouting is important at multiple different times of the year — it’s not something we’re just considering early in the season. The idea is that for scouting, first of all you want to consider it on a field-by-field basis.”

Even before going out to the field, think back to what the conditions were last year, especially the weeds that went to seed — if there were any weedy escapes that entered the seed bank, they’ll come back to haunt you this year. Escaped weeds that have gone to seed are especially important to consider in minimum or zero-till situations because the seed lands on the soil surface and is ready to germinate the following spring.

Story continues below video:

Moisture conditions are also important, says Geddes. “One of the big potential issues will be with dry conditions and the potential for herbicide carryover,” says Geddes. “So that gets into crop safety, so this year especially it’ll be really important to think back to what you were growing on that field the previous year, what herbicides were applied the previous year.”

Under dry conditions, certain herbicides can carry over for up to two years, so it’s important to check the herbicide’s information, which is available in the provincial crop protection guide, or on the herbicide’s label.

“Herbicide breakdown is usually related to moisture levels and also temperature as well,” explains Geddes. “So you almost need the combination of having enough moisture, and it has to be warm enough for microbial activity to break down those herbicides over time.”

Snowfall can contribute to herbicide breakdown, but soils are still cold at the time of snowmelt, and microbial activity won’t occur at that temperature to break down any remaining herbicide residue.

The critical weed-free period, when canola is emerging and putting on vegetative growth before having a chance to close the canopy, is critical to protect the crop from competition and to protect yield. Geddes says that it’s important to think about the weed spectrum that’s present in the field — which comes back to scouting — and that will help determine which herbicides will best manage weeds in that field.

It’s also important to think about the residual activity of a herbicide you’ll use says Geddes. Using a herbicide that has residual activity, will help take selection pressure off the post-emergent herbicide, but it’s also important to match the herbicide with the weeds present in the field, and any resistant weeds within that field.

“When we’re talking about mixing herbicide modes of action, or rotating herbicides, or layering herbicides, it’s one thing to layer herbicides or the modes of action, but it’s another thing to make sure those modes of action have efficacy on the weeds in that field,” adds Geddes.

Wake up with RealAgriculture

Subscribe to our daily newsletters to keep you up-to-date with our latest coverage every morning.

Wake up with RealAgriculture

Other Episodes

Canola School (view all)Season 13 (2021) Episode 27

Please register to read and comment.

Privacy Preference Center


Necessary cookies help make a website usable by enabling basic functions like page navigation and access to secure areas of the website. The website cannot function properly without these cookies.

gdpr, __cfduid, PHPSESSID, wordpress_test_cookie, woocommerce_items_in_cart, woocommerce_cart_hash, wp_woocommerce_session, wordpress_logged_in, wordpress_sec, wp-settings, wp-settings-time, __cf_mob_redir, wordpress_cache, realag


Measuring interactions with the ads on the domain.



These are used to track user interaction and detect potential problems. These help us improve our services by providing analytical data on how users use this site.



Preference cookies enable the website to remember information that changes the way the website behaves or looks, like your preferred language or the region that you are in.

chartdefaults, comment_author, comment_author_email, comment_author_url
JSESSIONID, _os_session,anonymous_votes,csrf-param,csrf-token,user,user-id,user-platform,intercom-session,intercom-lou,intercom-session
personalization_id, tfw_exp


Register for a RealAgriculture account to manage your Shortcut menu instead of the default.