Physiological leaf spot (PLS) appears as round or oval lesions that may be yellow or bleached white to gray in color. Lesions may also have a dark center with a narrow chlorotic (yellow) halos and tend to be more numerous toward the tip of the leaf blade. PLS lesions are often found in the upper canopy, and missing or rare on lower leaves. There are a number of winter wheat fields in southern Alberta in June 2025 that are suspected to have PLS as illustrated below.
Three Factors Favoring Physiological Leaf Spot (PLS):
- Cultivar susceptibility: nearly all wheat varieties can exhibit PLS, but some varieties are more prone to it.
- Insufficient chloride: soils with inadequate chloride levels, or where chloride is unavailable to the plant, are sometimes more severely affected.
- Fluctuating weather conditions where overcast, cloudy days are followed by sunshine-intensive days usually trigger this physiological response.
Preventing PLS:
- Fungicides are not effective because this condition is not caused by a fungus.
- Checking Cl levels in plants and soil – and supplementing deficient areas with Cl fertilizers can help avoid or prevent PLS. However, it may not provide a yield benefit. Chloride levels in soil of > 30 lb/ac in the top 24 inches are generally sufficient. For information on Cl fertilizer recommendations, see the MT AgAlert (May 15, 2025): Physiological and Fungal Leaf Spots in Winter Wheat
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