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That’s a tough decision. We’re heading into the ideal time for seeding canola based on past research and crop insurance data. Manitoba crop insurance numbers show that canola seeded the first two weeks of May typically yields the highest. The table below, taken from the Canola Council of Canada factsheet Seeding canola: The ideal timing, shows the yield and quality benefits from seeding early. The same factsheet lists these potential benefits of early seeding: The crop is out of the ground at or before warm season weeds get going; the crop can reach maximum leaf while day lengths are moving toward the June 21 peak; the crop flowers in the early part of summer, hopefully avoiding hottest temperatures that can cause flowers to abort; and the crop can mature before early fall frost.
But…
This year, even those canola crops seeded this week — which is considered “early” — will not be out ahead of weeds. Perennials, winter annuals, annuals and volunteers are emerging already. So when weather returns to warm and dry, should growers start seeding right away or control the weeds first? Clark Brenzil, weed specialist for Saskatchewan Ministry of Agriculture, says at this point, controlling weeds first is more important to yield potential than getting the crop seeded first.
Research by John O’Donovan shows that weeds emerging a week before the canola crop can cause up to 50% yield loss unless they’re controlled. Many fields are in that situation this year. See second the graph below.
Growers waiting for wild oats to emerge before spraying their pre-seed application, may need to increase the rate of pre-seed burnoff if winter annuals are close to the bolting stage. Glyphosate and CleanStart are the only pre-seed burnoff products registered for use ahead of canola. Check your crop protection guide or product label for more details on adjusting rates for specific weeds and growth stages. For detailed tips to help in a decision to seed or spray first, download the factsheet at this link. 
