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Old Disease, New Problems

John, who farms 7,000 acres of wheat and lentils near Consul, Sask., didn t like the look of his spring wheat crop. He called me at the beginning of July after he noticed orange stripes and tancoloured spots had formed on some of the plants leaves.

I ve heard of major disease pressure south of the border, in Montana, he told me. There was a huge rust outbreak in winter wheat. I m wondering if this is what s in my spring wheat, he said.

Farmers located in the southwest corner of Saskatchewan haven t really had to worry about disease pressure of this kind on their cereal crops. Recently, this has changed. If my suspicion was correct, John s crop could be under threat.

John was right to be concerned. As soon as I walked into the field I found orange-yellow pustules on the plants, extending the entire length of the leaves, forming stripes. The oldest leaves on the plants were most affected, but the infection was moving up toward the penultimate leaves the crop had not yet reached the flag leaf stage. I also noticed some tan spots forming on the leaves.

From what I could tell, John had two problems. First, the small, tan-coloured spots were caused by the fungusPyrenophora tritici-repentis.The spots begin as tiny brown flecks, which grow into lens-shaped areas up to 12 millimetres in length. A spot is sometimes surrounded by a yellow halo, and often develops a dark brown centre. Plants heavily infected with this leaf spotting disease, called tan spot, can wither and die.

The other disease affecting John s spring wheat was not difficult to diagnose either. The orange-yellow stripes were a telltale sign that his crop had been infected by stripe rust, caused by the fungusPuccinia striiformis.

Also known as yellow rust, this disease is typically problematic for producers in the southern United States, but not a cause for concern in Saskatchewan. Recently, however, stripe rust has been showing up in farmers fields more often and earlier in the growing season in Alberta, British Columbia, and now Saskatchewan. Usually, air currents carry spores from infected regions in the United States to fields in Canada, and symptoms appear one week after infection, usually in late summer. But something different was happening here.

What s rust doing in my field so early in the summer? In fact, what s it doing here at all? John asked me. He also wanted to know what he could do about it and what was going to happen to this crop.

These were good questions, and questions other producers in western Saskatchewan would want the answers to this season.

What was stripe rust doing in John s spring wheat crop in an area not typically affected by the disease and so early in the growing season? What can he do about it, and is it too late for his crop to be saved? Send your diagnosis toGrainews,Box 9800, Winnipeg, MB, R3C 3K7; email [email protected] or fax 204-944-5416 c/o Crop Advisor s Casebook. Best suggestions will be pooled and one winner will be drawn for a chance to win aGrainewscap and a one-year subscription to the magazine. The best answer, along with the reasoning which solved the mystery, will appear in the next Crop Advisor s Solution File.




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