Volume 39, Number 10 | APRIL 15, 2013
$4.25
PRACTICAL PRODUCTION TIPS FOR THE PRAIRIE FARMER
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Blackleg in canola evolving As the blackleg pathogen changes in Western Canada, an “R” rating for blackleg resistance may not be as meaningful as you expect BY ANDREA HILDERMAN
I
f there is one thing farmers can count on it’s that when you’re dealing with biological systems, generally there is no “win.” This certainly is appearing to be the case when it comes to blackleg in canola in Western Canada. Blackleg in canola is caused by the fungus Leptosphaeria maculans and it has spread to all canola growing areas in Western Canada. Blackleg resistance has been bred into canola varieties and it’s very important to understand that the pathogen was fairly well controlled by those varieties, however, that will not continue for very much longer.
NEW RACES OF BLACKLEG Since 2003 the blackleg pathogen has started to change. New races of blackleg are overcoming the resistance of those varieties grown in Canada. Selection pressure on the pathogen has come from: • tighter rotations; • minimum till and other similar practices; • inoculum kept on stubble for the following season; and,
• the pathogen reproducing sexually leading to mutations and new races. Dr. Dilantha Fernando is a professor of plant pathology at the University of Manitoba. He has been studying the blackleg-causing pathogen for many years. “We are seeing an increase in new races of blackleg across the Prairies,” Fernando says. “No one province can be singled out as a particular problem, it is as widespread as canola itself.” Fernando’s laboratory has been monitoring the pathogen. It’s changing and breaking down most of current resistance bred into canola varieties. “For 30 years or more, the same genes have been used for blackleg resistance in canola regardless of who bred the cultivars,” Fernando says. “It has been relatively easy for the pathogen to break down and overcome the resistance because most cultivars use the same gene, essentially.” Farmers may find this confusing because varieties are being rated “R” or resistant to blackleg. Fernando explains where this anomaly lies. “The resistance rating is true. To the extent certain few isolates of the blackleg pathogen are used to test cultivars prior
Blackleg on canola stems. to registration, but not all the new races that are cropping up in the field.” A farmer may see significant disease in an “R” rated canola variety if his fields are infected with one of the new races of blackleg. And this is how the problem will become worse. The new races will cause disease on varieties considered resistant. Inoculum will be left on the stubble providing more
chances for sexual reproduction for the fungus, leading to potentially more races and more disease.
FUNGICIDES Fungicides are an option to reduce the disease levels of blackleg in canola, however, they will not provide 100 per cent control. Additionally, application timing needs to be precise.
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Fernando has done work in this area, in collaboration with Alberta and Saskatchewan scientists. “It is also disappointing to note that while fungicides might give some control of the disease,” he says, “they are most likely not going to provide any economic benefit to the producer — we haven’t seen any significant yield increases as a result of using a fungicide.” But » CONTINUED ON PAGE 4
Wheat & Chaff ..................
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Features ............................
5
Crop Advisor’s Casebook
6
Columns ........................... 14 Machinery & Shop ............ 19 Cattleman’s Corner .......... 24
DIY variable rate
ANGELA LOVELL PAGE 11
Spring farm boot challenge
FarmLife ............................ 28
SCOTT GARVEY PAGE19
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