Solved – The Wrong Side of the Road
I had an interesting situation come up last year at the end of June when a producer from northwest of Portage la Prairie called me about his spotty field of canola. Ron, who farms 1,500 acres of canola, beans, oats, wheat and winter wheat, told me one field of his canola was healthy and growing on schedule, but the other field, separated by a road, was not looking at all well.
When I paid Ron a visit, one side of his field did look thin and randomly populated. Some areas had thick stands while others had five or fewer plants per square metre. But just across the road, the same canola variety seeded under the same circumstances had produced a completely healthy stand.
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When I walked through Ron’s problem field, the canola plants looked spindly, and some were falling over or broken off at soil level.
After some investigation, Ron and I were able to rule out cutworms, and the plants showed no symptoms of blackleg
— and he had used an R-rated seed variety for the disease.
The healthy stand across the road helped eliminate the possibility of poor germination, but I checked the seed lot just to be sure.
Ron had re-seeded this field with canola when his wheat crop was washed out. I considered if his thin canola growth could be caused by stress from excessive moisture, but the canola across the road would have been affected as well. This led me to think about the rotation history of Ron’s field.
The year before the wash out, Ron had planted canola and before that wheat, beans, and winter wheat. I had a sneaking suspicion that Ron’s problem was still being caused by blackleg, even in a field seeded with a resistant variety of seed.
A tissue test confirmed my hunch. Blackleg was destroying Ron’s field, but surprisingly it was a new strain never found in Manitoba before. Ron, an experienced producer, thought he would be safe planting canola again in the washed-out field because he was using a resistant variety of seed, but he did not count on a new strain of blackleg.
Crop rotation can be a very important ally when facing the enemies of disease and pests. Planting canola two years in a row can significantly increase your chances of crop damage due to disease and pests. Also, try to avoid seeding or re-seeding in cool, wet conditions when possible.
Also make sure you are using a proven R-rated blackleg variety, even though in Ron’s case the resistance didn’t prevent damage caused by the new strain.
Unfortunately for Ron, the blackleg in his field led to a huge yield loss. Blackleg survives in slowly decomposing canola stubble, so I would suggest a four-year rotation between canola crops. This may help prevent loss from disease and pest pressure.
Daniel Bolton is a crop input manager at Richardson International in Dundonald, Man.
