Blackleg, a fungal disease of canola, is getting away with murder. That’s right, murder. This fall, dead, brittle canola plants at swathing or harvest are being attributed, sometimes very wrongly, to sclerotinia infection when, in fact, blackleg is to blame. It’s likely been happening for years, Clint Jurke, agronomy specialist with the Canola Council of Canada, says. “We hear reports of blackleg infection every year at varying levels,” he says, but infection is likely far more common than many farmers realize.
That’s because a canola plant killed by blackleg can, at first glance, look very similar to one killed by sclerotinia. If you get down, pull up some plants and clip the stems, however, and the differences are striking.
Why does it matter, though? A dead plant is a dead plant. Well, yes and no. For one, the spray timing for blackleg is at the two- to four-leaf stage and products that protect against sclerotinia do nothing for blackleg and vice versa.
But before we even talk about spraying, we need to back up a step or two. First, the reason blackleg persists year to year is complex but is due at least in part to tight canola rotations. “The blackleg pathogen will survive as long as there is canola stubble in the field. For Western Canada, that usually means a one in four rotation is recommended, as that’s how long it takes for canola stubble to fully break down,” Jurke says.
The second aspect of the disease spread is genetic resistance, or rather, the pathogen’s ability to overcome it. “Blackleg can reproduce sexually, and so can overcome genetic resistance quickly,” Jurke says. Farmers are encouraged to not only rotate canola one out of four years, but also to rotate varieties. The idea there is that different varieties may have different forms or multiple forms of resistance. Does that mean choosing a different seed company all together, though? Jurke says we ‘ll know more in early 2013 about the types of resistance in the canola population currently available. Until then, it’s a good idea to, at a minimum, rotate the variety you grow each time on each field.
Just prior to swathing or just after harvest is a great time to scout for blackleg, so get out there now, Jurke says. Determining blackleg levels by field is the first step in developing a management plan for the disease going forward.
For tips on early detection of blackleg and to determine at-risk fields, click here.
For help in identifying and rating blackleg infection of canola stubble, watch this video from the Canola Council of Canada.
If you cannot see the embedded video below click here.