To spray or not to spray? It’s a tougher question when it comes to sclerotinia in canola than for most other crop diseases.
Last year, the high levels of sclerotinia many forecasters called for didn’t materialize. This year’s disease levels, and farmers’ decisions about going to the expense of spraying to control it, will mainly depend on the weather.
Will sclerotinia be a big problem in 2014? “We really don’t know for sure until the end of the season,” said Faye Dokken-Bouchard, Saskatchewan Agriculture’s provincial plant disease specialist. “All we have are maps that show what we’ve seen in past years.”
Saskatchewan’s sclerotinia maps from 2013 show few hot spots, although many experts had called for high levels of the disease last summer.
Tim Gardner, a senior market development specialist with Bayer CropScience, realizes farmers might think he’s crying wolf when he says he thinks levels will be high this year. He had also expected higher levels of disease in 2013. “I thought we had all the environment out there last year, and it just didn’t materialize.”
This year, Gardner said, all of the factors are in play for higher levels of sclerotinia. “I have a hunch we’re at pretty high risk in a lot of areas.”
The persistence of a two-year canola rotation may contribute to disease pressure. “We’re running tighter rotations in the West. There’s no doubt about it,” Gardner said.
Despite recommendations that farmers seed canola in a field only once every four years, many of the canola acres seeded in 2014 may have also grown canola in 2012, the year Gardner said “was the worst level of sclerotinia I’ve seen in all my years.”
Since sclerotinia’s sclerotia can survive for five years in the soil, wet weather before and during canola flowering could give sclerotinia a chance to thrive.
Sclerotinia has been a problem “almost every second year,” Gardner said. “It’s almost like we’re following it around all the time.”
Decisions about sclerotinia control are complicated by the fact that it is monocyclic — a disease with only one cycle per season. With other diseases, Dokken-Bouchard explained, you can see the symptoms, then spray to prevent an additional disease cycle in the same growing season. With sclerotinia, there is only one outbreak each year, so farmers need to control the disease before it happens.
Since farmers can’t spot symptoms on their growing crops, the best place to look is the weather forecast. “The trend goes up and down with the weather conditions,” said Dokken-Bouchard. “We can’t predict the amount of disease any better than we can predict the weather.”
It’s not easy, but it is possible for farmers to find sclerotia in the soil. “You can scout for the mushroom-like apothecia,” Dokken-Bouchard said. “Then you know the inoculum is there.”
But keep in mind, Gardner said, “they are quite small” (about half a centimetre). “And unless you have a lot of disease pressure, they’re not always easy to find.”
There are other factors to consider: field history and the level of disease pressure in the field from previous years are important. Crop health also matters.
“If you have weak skinny plants with lots of spaces between then you’re not going to have as much disease pressure,” Dokken-Bouchard said. “If you have good conditions for crop development you probably have good conditions for disease development too.”
A lot of things about Prairie canola crops have changed over time. Using more fertilizer, seeding better genetics and switching to zero-till practices have increased canola yields, but have also contributed to an environment where sclerotinia can be more prevalent. “The potential risk is everywhere,” Gardner said.
SaskCanola continues to fund research into sclerotinia; it has an interactive tool available online to help farmers make decisions about sclerotinia control.