Good afternoon Brian,

We received Your question about your Cleveland pear tree. The tree appears to have some type of fungal disease. There are a variety of different fungi that can cause these. One of these is Leaf spot which is a fungal disease of ornamental pears caused by a variety of different fungi. The disease appears in the form of scattered but definite, oval to round spots on the leaves. Leaf spot is most evident during summer and persists during periods of light and frequent rainfall, humidity, and fog. Leaf spot leads to premature defoliation in trees, gradually weakening the tree and stunting growth. The presence of leaf spot increases tree susceptibility to a number of other diseases such as bark borers and winter injury. Preventive measures include the application of ammonium nitrate fertilizer and pruning trees to improve air circulation.

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 leaves of the trees are two important things you can do to minimize the problem.

Following are links to research based information from universities relate to leaf spot diseases of ornamental pears:
Apple Scab:https://www.canr.msu.edu/ipm/uploads/files/WoodyLandscape_PDFs/AppleScab.pdf
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7413.html

Other leaf spot diseases of pear are Fabraea, Pear Scab,and Entomosporium leaf spot.
Fabraea: https://www.canr.msu.edu/ipm/diseases/fabraea_leaf_spot
Pear Scab: https://www.canr.msu.edu/ipm/diseases/pear_scab
Entomosporium leaf spot:
http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/entomoslfspt.html

You may wish to contact a certified arborist to treat the tree. You can find a certified arborist by searching by zip code at:https://www.treesaregood.org/findanarborist/arboristsearch

Hope this information is helpful. Feel free to contact us if you have other questions.

Linda, Weld County Colorado Master Gardener