Cause The fungus Taphrina bullata has been reported from Washington. Not a common issue in commercial production of pears likely due to pest control measures targeting other disease and insects.
Symptoms Large, light-green to yellow, irregular blisters form on the upper surface of leaves. A white fungal bloom develops on the concave underside. The leaf blisters caused by eriophyid mites (pear rust mite, Epitrimerus pyri) are more common, smaller, can be reddish and are numerous on the leaf surface.
Reference Petrýdesová, J., Bacigálová, K. and Sulo, P. 2013. The reassignment of three 'lost' Taphrina species (Taphrina bullata, Taphrina insititiae and Taphrina rhizophora) supported by the divergence of nuclear and mitochondrial DNA. International journal of systematic and evolutionary microbiology, 63:3091-3098.