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Crop Advisor’s Casebook – for Mar. 14, 2011


Mid-June last year, a farmer concerned for his wheat field called me for some advice. Worried he’d put too much stress on his plants — causing them to yellow — by spraying herbicide when the field was waterlogged, he asked me how he could fix the problem.

“I wanted to give the plants more opportunity to recover,” he said, “but the weeds were getting big and I was coming to the end of my safe herbicide window,” said Doug, who farms 2,300 acres of wheat, oats, canola and soybeans south of Brunkild, Man.

Doug explained it had poured with rain the last two weeks of May, hammering his field with six inches of water. The field hadn’t had a chance to dry up before Doug sprayed.

When I arrived at Doug’s wheat field, I thought it looked pretty sick. I noticed a distinct yellowing of the leaves, particularly the older leaves. The yellowing was spread evenly throughout the field — although it appeared worse in the lower lying areas. Some of the deeper ruts still had water in them, but the majority of the field had drained.

I told Doug one of the possible causes for the leaves of his plants turning yellow could be stress from the excess moisture, and, adding to that, more stress from the application of herbicide. Another possible factor causing Doug’s sick wheat could be nutrient deficiency.

In total, Doug’s field had been fully saturated for over three weeks with two stretches of three to four days of standing water. He’d applied 110 pounds of anhydrous ammonia (NH3) in the fall. The following spring, Doug applied 90 pounds of fertilizer granules (nitrogen, phosphorus, sulphur and zinc) at seeding for a total analysis of 122-30-0-13.5.

Leading up to the heavy rains, growing conditions had been optimal, so germination was terrific. When he sprayed his field with herbicide, Doug applied a tank mix on his crop generally considered to be safe.

My final observation that day, and my first clue as to what was causing the problem, was small patches in his field located at a slightly higher elevation had already greened up a bit.

For the next five days, Doug and I watched his field carefully. The yellowing continued to develop. Now I was pretty sure I knew what the problem was.

Why are Doug’s wheat plants turning yellow and how can he fix this problem? 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 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.

ScottWilliamsisacropinputmanagerat RichardsonPioneerLtd.inMollard,Man.



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