Q: How do I determine the correct bloom stage in canola to apply a sclerotinia fungicide?
A: Proper timing of fungicide for sclerotinia control requires regular scouting. The recommended timing is application at the 30 per cent bloom stage. Application prior to this stage can result in reduced control as petals susceptible to infection have yet to emerge. Later application can also show reduced levels of control as petals potentially infected with disease have begun to drop and can get caught in the leaf axis.
If many acres must be covered, not all fields can be sprayed at the 30 per cent stage. In this case, start at 20 per cent bloom. Spraying after the 50 per cent bloom stage is not always economical.
To identify the 30 per cent bloom stage, find the main raceme (usually the tallest) of a single canola plant and count the number of flowers and aborted florets up the stem. Start at the bottom of the main raceme and count the pods, aborted flowers and open flowers up to the green buds at the top of the plant. Sixteen to 20 flowers or aborted florets open on the main raceme corresponds to the 30 per cent bloom stage. Twelve to 16 flowers open on the main raceme corresponds to the 20 per cent bloom stage, and 10 to 12 flowers is the 10 per cent bloom stage.
Repeat the flower counting process at multiple locations in the field. In good weather up to four new flowers can open in a single day, so check regularly.
Jordan Peterson, P.Ag,CCA, is a manager of agronomic services for Nutrien Ag Solutions in northern Alberta.