The mountain ash (Sorbus species) may come from the mountain but it is not really an ash tree (Fraxinus species). It is actually a close relative the apples (Malus), pears (Pyrus) and roses (Rosa) since it is a member of the Rose Family (Rosaceae). Therefore, it is susceptible to many of the same diseases of its relatives including the fungal leaf disease, apple scab and the more serious bacterial disease, fireblight. The better news is, that since it is not a true ash, it does not get attacked by the Emerald ash borer which is in the process of killing millions and millions of ash trees throughout the Midwest.
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