Farmers who thought they had kissed blackleg goodbye will have to get used to living with canola’s ugly partner again.
A new strain of the disease has been appearing in farmers’ fields and it isn’t going to disappear.
“We didn’t get rid of it,” said Canola Council of Canada agronomist Jim Bessel.
“It’s there and will always be there.”
Many farmers thought blackleg had been permanently controlled by the development of resistant and moderately resistant canola varieties.
Blackleg devastated brassica napus crops in the 1980s because the Westar variety, then the overwhelming favourite among farmers, had little resistance to the dominant family of blackleg.
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Known as pathogenicity group 2, or PG2, the disease was controlled and then suppressed by new resistant varieties.
For years, the threat of blackleg faded because the varieties fought it off so well.
But the disease reappeared last summer, damaging some crops.
Tests showed the presence of PG3, a blackleg strain common in Europe but that prairie canola varieties are not armed to resist.
University of Manitoba scientist Dilantha Fernando began surveying suspected blackleg outbreaks last summer and is continuing this summer to find out how widely PG3 is appearing.
Seed companies have begun integrating PG3 resistance into their breeding programs.
In the meantime, canola council agronomists urge producers to stick to good rotation practices and urge wayward producers to return to the tried and true path.
“This is a heads up to follow a proper rotation,” said council agronomist Derwyn Hammond.
Added Bessel: “Be aware and practice the practices we’ve been preaching. Keep (rotations of canola) to one in four like we’ve been saying for years.”
Blackleg exists in nature in many strains, but most cause few significant problems.
Howard Love, a seed variety developer with SW Seeds in Saskatoon, said he thinks PG3 may have been on the Prairies for years.
“I don’t think anyone should think this is a problem that just arose last year.”
He also said the appearance of new virulent strains of common plant diseases is to be expected.
“We don’t see this as a particular crisis,” he said.
“This is typical of pathogen disease and cultivar interaction.”
Hammond said emerging PG3 strains have not neutralized all the blackleg resistance in prairie canola varieties.
“If it’s an MR (moderately resistant) it may perform more as an MS (moderately susceptible),” he said.
“It’s not a complete collapse of the resistance.”
Bessel said the development of resistant varieties in the 1980s and 1990s may have led producers to think they could get away with shorter rotations.
“When you push things, nature pushes back.”
Hammond said blackleg’s sexual stage allows it to develop new strains that, put under pressure by resistant varieties, can break through that wall of resistance.
“If you take highly resistant (canola) varieties and grow them in a short rotation, you’re selecting for the most virulent (disease) strains.”
Many prairie canola crops have not yet emerged and blackleg’s presence won’t be seen for weeks, but Bessel thinks most farmers won’t be badly affected.
Most are sticking to careful rotation plans, he added, which has helped make canola a permanent part of most farmers’ plans.
“If we weren’t doing it right we’d have big wrecks out there like we used to – and we don’t,” he said.
