I have two serviceberry shrubs, both of which produced normal fruit initially, but then both developed what appears to be an orange colored fungus growing on the fruits. I'm not sure what this is or how to treat it assuming treatment is necessary.
Frederick County Maryland
This is a fungal disease called cedar-quince rust, Gymnosporangium clavipes. We are getting a lot of reports of rust disease this year, as our wet weather has been favorable for it. Serviceberry is in the rose family, so it is susceptible to many of the same disease and insect pest problems that are seen in other species within the family (e.g. apples and pears). The alternate hosts of this disease are Eastern red cedars (Juniperus virginiana), Common juniper (J. communis), and Creeping juniper (J. horizontalis). The fungus carries out its lifecycle between the two host plants.
If it is possible to remove Junipers in the vicinity, that can help to control the rust on your serviceberries. Often this is not feasible. Prune off and dispose of the infected berries to help control the spread of the fungal spores. That is really all you can do.