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Two weeks after Jack — a Manitoba farmer with a 4,500-acre grain operation in the Killarney area — noticed his neighbour spraying the volunteer winter wheat crop adjacent to his own crop, Jack called me to investigate what he thought were signs of spray drift damage to his winter wheat plants.

“I saw my neighbour spraying his crop in early flag a couple of weeks ago, and I’m sure whatever he sprayed is killing my crop,” Jack told me.

That first week of July, Jack’s winter wheat plants were at the late flag to early heading stages. The plant population appeared to be thinning out, and the plants were stunted in growth with lines of yellow to white chlorotic streaking on their leaves running parallel to the veins.

The majority of the affected areas in the field occurred in random patches next to Jack’s neighbour’s field. His neighbour had let his volunteer winter wheat field go to yield due to the wet conditions the past fall and spring. I noticed that crop was also showing the same signs of damage as Jack’s crop. But the broadleaf weeds in both fields and the grass strip separating the two fields did not exhibit any symptoms of damage.

We asked Jack’s neighbour to join us in examining the two fields. He was surprised and concerned about the symptoms now present in both fields, but said it was impossible that spray drift was the cause. Records indicated that Jack’s neighbour had applied a fungicide to his crop, one that would not have had any negative effects on wheat, and the wind had been blowing in the wrong direction for the sprayer to have caused drift damage. However, I thought the wind had played a role in damaging Jack’s plants.

Taking the excessive moisture of last fall and this past spring into account and the patch-like occurrence of the damage in the area near the boundary between the two fields, I thought it most likely that we were dealing with an infection, and one that was spread by air currents.

“We’ll have to wait for lab results to confirm it, but I think the volunteer crop has created a green bridge for carriers of a viral disease — which have infected both of your crops,” I told Jack and his neighbour.

“You can’t see them, they’re microscopic,” I said to Jack as he started to examine the surrounding wheat plants. “And the virus they carry can cause losses of a few bushels per acre to complete crop failure.”

What disease has infected Jack’s field and what is vectoring the virus? Send your diagnosis to Grainews, 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 a Grainews cap and a one-year subscription to the magazine. The answer, along with the reasoning which solved the mystery, will appear in the next Crop Advisor’s Solution File. †

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