|K-State Research and Extension Horticulture Newsletter||
During the summer, many people notice yellow-orange spots on the leaves of their ornamental or fruiting pear trees. These spots begin in the late spring on the upper surface of leaves, approximately 1/8 to ¼ inch in diameter. Gradually they enlarge and turn orange during the summer months. Though these spots resemble the cedar-apple rust spots on apple leaves, they are caused by a slightly different organism. Pear leaves are infected with cedar-hawthorn rust rather than cedar-apple rust. Though cedar-hawthorn rust is different than cedar-apple rust, both diseases work the same and the control is exactly the same as well. This disease causes primarily only aesthetic damage on ornamental pear trees, and is considered a nuisance problem, rather than causing significant harm to the health of the tree. Therefore, control is optional, and generally not recommended unless the tree experiences substantial leaf drop.
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Ward Upham runs the Horticulture Response Center in the Department of Horticulture and Natural Resources at Kansas State University. Other contributors include K-State Extension Specialists.