Physiological Leaf Spot is suspected in a number of winter wheat fields in Southern Alberta.
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.
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: Physiological and Fungal Leaf Spots in Winter
More information is available on the Prairie Crop Disease Monitoring Network
Wheat https://www.montana.edu/cope/email-format/admin/view.php?draft=13640&uid=68261a2c4af5d7.78080120
Also see Fertilizer Facts: April 1997, Number 16: https://landresources.montana.edu/fertilizerfacts/documents/FF16WWLeafSpot.pdf
Physiological leaf spot in cereals: https://www.topcropmanager.com/physiological-leaf-spot-in-cereals-14969/