Ornamental pear can get a number of leaf spot diseases, apple scab being one of them. Cleaning up fallen leaves and angling sprinklers so they do not wet the trees leaves are two important things you can do to minimize the problem.
Here is spray information on managing apple scab on apple, crabapple and pear:
"Fungicides must be applied preventively to successfully manage apple scab. Because spores are released so early in the growing season, fungicide sprays must begin when the first green leaf tips emerge in spring. Sprays should be repeated until petal drop for crabapple. If the tree is healthy and free of leaf spots at this point, further treatments are unnecessary.
Check fungicide labels for the recommended spray interval. Most labels offer a range of days to wait before spraying again. (e.g. 7 to 10 days after spraying, you will need to spray again). Several factors affect what spray interval is most appropriate. In plantings where there was a severe scab infection the previous year, use the shortest interval. In plantings where scab has not been a problem, a longer interval will probably give adequate protection. In addition, if the weather is dry the longer interval is acceptable, whereas during rainy weather the shorter interval is preferable.
Once leaf spots appear in the tree, fungicides provide very little control of disease. There is no point in spraying an already heavily infected tree. Contact a certified arborist to apply fungicides to large trees. Chemical treatments are listed in the table below.
The name of the plant being treated MUST BE LISTED on the fungicide label or the product cannot be used! Some products are registered for use on ornamental crabapples but are not safe to use on crabapple or apple fruit intended for human consumption. Always completely read and follow all instructions on the fungicide label."
The complete article, including the table that lists products, is here---
Other leaf spot diseases of pear are Fabraea, Pear scab, Rust, Entomosporium leaf spot. You may want to use the MSU Diagnostic lab to positively identify future problems- their website is here---
If your tree is large you will need a professional who has tools with enough power to reach the top of the tree. You can find certified arborists here---
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