In oilseed crops like canola and flax, timing is crucial for application of herbicides and fungicides to help protect yield. Proper herbicide and fungicide application timing based on the product label often comes down to a grower’s experience and knowledge of what growth stage is appropriate — and what that actually looks like in the field.
For example, the recommendation for canola is typically to target a fungicide application anywhere between 20 and 50 per cent bloom on the canola stem, and ideally at 30 per cent bloom. But what does that look like?
Basically, says Manitoba provincial oilseed specialist Dane Froese, that’s when the top of the canola plant has 25 open flowers or pods formed on the main stem. “If growers are seeing a bit more than those 25 flowers and some early pods formed on that main stem, they might be a little on the later side and may need to expedite the fungicide application and/or process,” he says.
“For instance, if the ground is too wet for a ground application, perhaps an aerial application might be better suited at that time for efficiency and to achieve proper fungicide timing.”
On the other hand, if a fungicide is applied too early (around the 10 to 15 per cent bloom stage), growers could be wasting time and money because they won’t get the full benefit of the chemical.
“A fungicide in canola at flower timing is targeted for sclerotinia protection,” says Froese. “In order to prevent sclerotinia infection, or reduce the chance of infection, we’re really targeting the flower petals because they are a high sugar source and end up being food for the sclerotia infection of flowering canola. If there are no petals there, spraying a fungicide designed to coat petals and reduce sclerotinia infection means the producer would end up spending money on a product that won’t work as labelled or intended.”
Don’t be a drive-by scout
At harvest time, it’s not enough to be a drive-by field scout, adds Froese. “Looking at a crop and saying it’s brown so they should be able to harvest it in X number of days is not always correct,” says Froese. “A grower does need to understand that the field is ready for swathing, or potentially a pre-harvest desiccation application, at about 60 per cent seed colour change on the main stem. That’s looking at the main stem, moving from the bottom up; 60 per cent of those seeds need to have either turned or are starting to turn colour before that crop is at the correct stage to have the maximum dry matter accumulation.”
If growers cut the crop earlier than that, they risk locking chlorophyll into the seed and having a downgraded sample — there’s not as much dry matter accumulation yet, the crop is still slightly immature and yield could be lost by giving up bushel weight as a result of having a lighter or smaller seed at that time.
Know the products and what they’re for
When it comes to crop protection products, especially fungicides, says Froese, although timing is important, it’s also important to understand how the products work and the diseases they are targeting.
Flax is a good example. Flax is more sensitive to herbicide timing, so application when the crop is between growth stages one (emergence) and almost to five (stem elongation), before flowering and boll formation starts to occur, is ideal, says Froese.
“If growers spray herbicide beyond that point, they risk damaging yield and stressing the crop out,” says Froese. “Ideally, they want to try and target between stages one and four because stage five starts getting a bit late and can injure the crop and stay in that injured stage longer before resuming normal growth habits.”
Froese advises growers to watch for the number of true leaves that form on the spiral after the cotyledon, with stage four being when the third pair of true leaves is present. “By stage five the stem begins to elongate, so between stage four and five is the maximum we’d like to see in-crop herbicide application.”
Fungicide applications in flax are not assessed in the same way because they are usually for pasmo, a stem disease, so the fungicide is targeting green matter and not flower petals to protect the plant.
A note on canola growth stages
Canola and flax plant growth stages are numbered according to the BBCH decimal system. According to Canola Council of Canada’s Canola Encyclopedia, the life cycle of a canola plant is divided into seven principle stages and each stage has up to ten substages. Each growth stage represents a phase in the plant’s development, however, several of them overlap — one stage may begin before the previous stage has ended.
From the onset of budding, each growth stage is determined by examining the main flowering (terminal) stem. Timing and occurrence of different growth stages varies with growing conditions, location, species and canola variety. In general, when two stages overlap, growers should use the more advanced stage to base management decisions upon.
The length of each growth stage is influenced by temperature, moisture, light (day length), nutrition and variety. Research by the University of Manitoba has shown that temperature is the most important environmental factor regulating growth and development of canola in Western Canada.
A comprehensive list of the growth stages of canola can be found in Canola Council of Canada’s “Growth Stages of the Canola Plant” in the publication Canola Encyclopedia. The Flax Council of Canada’s Growing Flax publication contains flax growth stages in Chapter 4 called, “Growth and Development.”
Oilseed Growth Stages Resources
Find information online for determining growth stages of canola and flax: