Aster yellows is taking the blame for the yield drop in canola this year, but Alberta Agriculture plant pathologist Mike Harding thinks there were other factors.
The cool wet spring delayed seeding, so many crops were blooming when temperatures were over 30 C, Harding said.
“Aster yellows cut yields in some crops,” he said. “But in my opinion, sclerotinia caused most of the yield losses in canola this year.”
He doesn’t believe any of the fields he saw had enough damage to drop yields by more than about five per cent.
“Aster yellows is very easy to scout, he said. “I did see some crops that would likely have benefited from controlling the leafhoppers that carry the disease.”
“We had more leafhoppers than usual and a higher percentage than usual were infected with aster yellows,” said Alberta Agriculture pest specialist Scott Meers.
However, he doesn’t advise rushing to control leafhoppers. They don’t show up in significant numbers most years. They’re only a problem when a high percentage carries aster yellows but testing for the pathogen requires a DNA test.
Harding thinks heat was a culprit in the disappointing yields of many canola fields, but suspects the main problem was sclerotinia.
Everything lined up for sclerotinia damage,” he says. “We didn’t have a lot of rain, but we had quite a spell of unusually high humidity that made for wetness in the canopy — perfect for sclerotinia.
“I saw sclerotinia in just about every field I scouted this year. We had a long period when humidity wasn’t below 50 per cent at any time. It seemed dry, but under the canopy it’s different,” Harding said.
“Sclerotinia flew under the radar this year,” he says, “You need to check the crop, not just the weather. Any time you can walk through the crop at 10 or 11 in the morning and your pant legs are getting wet, conditions under the canopy are ideal for sclerotinia.”
Harding says tolerant varieties help, but tight rotations increase risk considerably. He advises switching into cereals for a few years if sclerotinia becomes a persistent problem.
“Economics are crucial in farming,” he says. “But, if you ignore the biology, especially the biology of pathogens, it can take a big bite out of the economics of your farm.”