This spring has been anything but typical in many parts of the prairies, and that is leading some producers to question whether they should change their weed control strategy.

“In a typical spring, early weed control in canola gives the best returns as it keeps the crop weed free during the cotyledon to four-leaf stage when it is most vulnerable to weed competition,” says Canola Council of Canada agronomist Derwyn Hammond. “However, this spring stressed plants and thin or uneven emergence issues are common in many fields.”

Drought or frost stress. Should I wait to spray?

My stand is thin and delayed. Can I wait and get the weeds with a single pass or will I have to spray multiple times?

The answers to these questions will be field specific, says Hammond, but the bottom line is still that weeds emerging ahead of or at the same time as the canola crop will cause the most yield loss. This is best summarized in the fact sheet at the following link: https://canola-council.merchantsecure.com/canola_resources/product36.asp

The Canola Council suggests growers keep these points in mind as they  evaluate each field on a case-by-case basis:

• The first step is to scout to determine which weed species are present, and at what growth stage and density. If canola plant densities are low, more intensive field scouting will help ensure that timely and effective weed control prevents weed competition from jeopardizing the remaining plants’ ability to compensate. The increased time to ground cover in thin stands will leave the crop vulnerable to weed competition beyond the typical four-leaf stage. Sequential applications of system specific herbicides may be required until there is full canopy closure.
• For crops under stress it may be best to wait for active growth to resume on the canola plants and weeds in order to get the best crop tolerance and efficacy. However, if field evaluation suggests weed pressure is high (and impacting yield), the benefit of removing the weed competition likely will outweigh potential crop tolerance issues.
• Stressed canola plants may begin reproductive growth earlier than normal (less vegetative biomass produced before initiating buds), and there has been some budding at the five-leaf stage in some fields. Waiting to spray may result in missing the application window if premature bud initiation and bolting occurs. Spraying at these stages can, in some cases, add stress to the canola plants, significantly reducing yield and delaying crop maturity --  a definite concern this year. This will vary depending on the specific chemistry, so growers should consult their company representatives.
• Some growers are noticing grassy weeds are present and need to be controlled, whereas broadleaf weeds have been slower to emerge. While research has shown that sequential applications are rarely economical, in this situation, it may be practical for growers to split apply herbicides. This is especially true in drier areas where weeds are aggressively competing for precious moisture.
• If herbicide dollars are limited, growers are advised to spray early with the first application and re-assess the need for a second application later. Some weeds (e.g. wild buckwheat) get more expensive and much tougher to control as they get bigger.
• Finally, when growers do decide to spray, they should make certain the product hits the target and the target only. “Ensure legal land descriptions and field directions are 100% accurate to eliminate misapplication errors,” says Hammond.  “Pay attention to boom height, nozzle selection, water volume, pressure, wind speed and direction. Check the following links for information on sprayer calibration and managing spray drift:

Calibration tips - http://www.omafra.gov.on.ca/english/engineer/facts/88-129.htm
Managing drift - http://www.ag.ndsu.edu/pubs/plantsci/weeds/a657w.htm
The following link has more general information on weed control in canola: http://www.canola-council.org/contents10a.aspx.

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For more information in your area, contact:

Derwyn Hammond, Manitoba Region, 204-729-9011

Jim Bessel, North Central and North Eastern Saskatchewan, 306-373-6771

Tiffany Gutzke, Eastern Saskatchewan, 306-231-3663

Doug Moisey, East Central Alberta and Northwestern Saskatchewan, 780-645-9205

Matthew Stanford, Southern Alberta and Southwestern Saskatchewan, 403-345-4852

John Mayko, West Central Alberta, 780-764-2593

Erin Brock, Peace Region, 780-568-3326

This media release 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; B.C. Ministry of Agriculture & Lands.