CROP ADVISER’S SOLUTION SOLVED — WHAT IS CUPPING THIS CANOLA?
Dave called me in June because he was worried about his canola. He had random patches throughout the field of plants in the three-to five-leaf stage. On closer inspection, the leaves in the patches seemed to be cupping and were turning purple around the edges and the backsides. He figured it was due to herbicide residue.
When we checked the canola, we realized most of the patches were in the sandy knolls of Dave’s field, where there is less organic matter and nutrient leaching is a possibility. He’d applied nitrogen, phosphorous and sulphur, following recommendations from a soil test from the previous fall.
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There was something about the leaf cupping and purple leaf margins that led me back to sulphur. Dave’s rate of fertilizer was about 110 lbs. of nitrogen and 12 lbs. of sulphur in a mid-row band and 35 lbs. of actual phosphate with the seed. The sulphur source was ammonium sulphate. We took soil and tissue tests which confirmed severe deficiencies of sulphur in the patches in Dave’s canola.
I suggested he apply ammonium sulphate on the crop as soon as possible, since it was still early enough to correct the deficiencies before too much yield was lost.
We talked about the importance of nutrient balance in crops, and that in order to maximize yield and make efficient use of applied nitrogen, especially with canola, it’s important to make sure other nutrients like sulphur aren’t lacking.
It’s easy to get a false high reading of sulphur on a soil test because there can be a few pockets in the field with high levels of sulphur, even though most of the field could be deficient. With the amount of rain in the area that spring and the previous year, a lot of sulphur had probably leached down in the sandier soil, making it unavailable to the canola seedlings.
On Dave’s soils, using some elemental sulphur as a sulphur source could make sense, since it is released more slowly and therefore not as prone to leaching. I suggested MicroEssentials S15, because it has a very low salt index for seed-placed safety and is an excellent balance of phosphate and sulphur for canola. It also uses both sulphate and elemental sulphur to ensure season long availability. Dave figured he’d give it a try, because it was simple to apply and the promise of saving his canola was worth the effort.
Sure enough, after Dave top-dressed his crop with a little more sulphur, the symptoms gradually went away with rainfall and, in the end, his crop yielded very well.
Make sure you learn from Dave’s mistake. If you are applying aggressive rates of nitrogen to maximize yield and profit, don’t forget to have other nutrients in balance. Use a variety of nutrient sources if they fit the situation. On Dave’s farm MicroEssentials is a great fit to help him grow a healthy crop and improve his bottom line.
Wes Anderson is a Richardson International agronomist in Corrine, Sask.
