Early weed control is the most economical and often the most successful. It reduces weed competition for nutrients and moisture, improving the yield potential for canola. Younger weeds are also easier to control and that control may be achieved with lower rates. Later emerging weeds have less impact on yield than those emerging with or ahead of the crop. For these reasons, in-crop weed control should occur as early as possible.
A possible strategy to control early weeds to maximize yield while also catching later germinating seedlings is split applications. This is an option with glyphosate on Roundup Ready canola varieties and Liberty on Liberty Link varieties. The first application of the split is best timed just as the crop is emerging. The second application, if necessary, can go on before the maximum crop stages for each herbicide system and at the optimum stage for control of the emerged weeds.
Here are the staging options for each herbicide tolerance system:
Roundup Ready: The window is from seeding to the 6-leaf stage. Two applications are an option, but the maximum application rate per season is the equivalent of 1.0 litre per acre of the original 356/360 g/L formulation in RR canola.
Liberty Link: The window is from cotyledon to early bolting. Set the rate based on weed pressure. Split application is an option, but the maximum allowable rate per season is 2.97 litres per acre.
Clearfield: The window is from the 2-leaf to the 6-leaf stages. Odyssey, Odyssey DLX or Absolute can be applied only once per season (no split applications) but have some residual activity.
Scout fields to see what weeds are present and at what size and plant density before choosing an appropriate rate and/or tank mix option. For example, Canada thistle is 3 to 4 times more competitive than wild oats and may require a special approach for effective control. Research from AAFC in Lacombe, Alta., shows it only takes 10 Canada thistle shoots per square metre to cause a 10% yield loss in canola. For more on this, read the Canola Council of Canada factsheet, “How many weeds are too many?”
Consult with your company representative to determine the appropriate rates and tank mix combinations for your situation and weed population, or click your province for a link to your guide to crop protection: Alberta Saskatchewan Manitoba.