Crop growth and development is variable within many fields in western Canada. Plus, thin plant stands are taking longer to cover the ground and weeds continue to compete in some fields. A common question being asked is can a field be sprayed after canola begins to bud? Each field should be considered on a case-by-case basis.
The first step is to scout. Scout the crop for signs of stress (e.g. moisture) and growth stage. Scout the weeds to determine what weed species are present and at what stage.
Weeds that emerge ahead of or at the same time as the canola crop will cause the most yield loss. The following link provides information on time of weed removal: https://canola-council.merchantsecure.com/canola_resources/product36.aspx
Stressed canola plants will begin reproductive growth earlier than normal (less vegetative biomass produced before initiating buds). Crop damage (flower blast) and yield loss can sometimes occur when herbicides are applied to a crop in bud or bolting stages. The potential for crop injury will vary depending on several factors including the product used, how it is applied (e.g. water volume, time of day) and the level of crop stress. However, weed pressure also causes yield loss. Scout the field thoroughly to determine average crop stage and to determine which stress is most limiting (weeds vs. compromised crop tolerance). Keep in mind that herbicide injury can also delay crop maturity, which is a definite concern this year.
The following link has more information on weed control in canola: http://www.canola-council.org/contents10a.aspx