LACOMBE, Alta. — Rain, more rain, high humidity and warm days have created ideal conditions for the development of sclerotinia in canola, says Alberta Agriculture oilseed specialist Murray Hartman.
High canola prices and a potential for high canola yields means farmers should seriously consider spraying for sclerotinia, especially if sclerotinia stem rot was a problem in previous years, said Hartman.
Unfortunately, sclerotinia isn’t visible on the plant until it’s too late to spray. Instead, farmers need to know how much sclerotinia was in their fields or neighbouring fields in previous years and make an educated guess.
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“Normally it doesn’t come from the field you’re planting,” he said.
There is a good chance of sclerotinia this year because of the high number of canola acres and last year’s higher than normal incidence of the disease.
“There’s a pretty big push on to spray for sclerotinia this year. It’s justified,” said Hartman.
Prices of $12 to $14 a bushel for canola means farmers need only a two bu. loss to pay for the roughly $25 an acre fungicide cost. A 40 bu. crop with a 10 percent loss will easily be paid for by spraying.
Last year, some producers had almost 20 percent canola yield loss from sclerotinia.
“With stronger prices, you get a stronger incentive for spraying.”
Canola is now blooming, and farmers need to decide quickly if they will spray. Hartman said it needs to be done when the crop is 20 to 50 percent in bloom. A canola field at the research plot in Lacombe was already too late to spray.
Sclerotinia fungus overwinters in the soil and begins its growth in wet soil in the spring. Spores released from the fungus can travel more than a kilometre and land on canola flower petals.
The petals fall into the canopy as the canola matures and stick on leaves and stems. This is when the disease begins to infect the plant.
“That’s the door where it gets into the plant.”
The longer the canola field stays in flower, the more susceptible the crop is to infection.
This year’s late, cold spring, which delayed emergence and created a variety of stages of canola, may make it difficult for farmers to decide when to spray.
Canola is in 10 percent bloom when about 10 flowers are open on the main stem and 15 to 20 percent bloom when 15 flowers are open.
Producers have several fungicide choices, and all can be applied by air or ground.
The challenge is booking aerial applicators because of strong demand this year, said Derwyn Hammond of the Canola Council of Canada.
Ground spraying is often preferable for most fields, if a high and narrow-wheeled spray rig is available and soil rutting isn’t too much of a concern.
A ground sprayer mounted with 12-inch tires and 100 foot booms will trample about a bushel per acre in a 50 bushel crop, for a cost of $12 per acre.
Hammond said wheel tracks and aerial applications are a reasonable cost when compared to a 10 to 25 percent yield reduction from the disease worth $60 to $150 per acre.
“Control is a good investment when it comes to sclerotinia. With prices where they are, there is a very good return on that investment.”
Aerial applications should be per-for med at the higher end of the plane’s water rates to ensure good canopy coverage.
