Physiological Leaf Spot suspected in a number of winter wheat fields in Southern Alberta
Dr. Michael Harding, Alberta Agriculture and Irrigation and PCDMN collaborator
June 9, 2025
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
Also see Fertilizer Facts: April 1997, Number 16:
Physiological leaf spot in cereals: Top Crop Manager, Features: Agronomy Diseases
MT AgAlert (June 7, 2024): Physiological and fungal leaf spots on winter wheat
North Dakota State University Crop and Pest Report (June 6, 2024): Leaf spots and discolorations in wheat
PCDMN In-Season Update (May 29, 2025): 2024 Plant Disease Issues to Watch Out For: Seed and Seedling Issues
PCDMN In-Season Update (June 24, 2022): Scouting and risk assessment recommendations for cereal leaf spot diseases
PCDMN In-Season Update (July 7, 2020): Scouting for cereal diseases: Risk and the need for a fungicide application