I have yellowish-orange craggy spots on my crabapple (native) and...

Asked July 15, 2013, 12:27 PM EDT

I have yellowish-orange craggy spots on my crabapple (native) and serviceberry. I believe it's Gymnosporangium globosum. I would like to keep them. What should I do? Thank you.

Dorchester County Maryland

1 Response

Sounds like your crabapple and serviceberry may be subject to a rust disease and there are several types which include cedar apple rust, cedar quince rust, and cedar hawthorne rust. It does not kill the trees but obviously are very disfiguring. This can be common in cool wet weather. In all cases, the disease has alternate hosts, one being a juniper tree or shrub and the other being a plant in the rosaceae family. The most common alternate host in this area is the Eastern Red Cedar which is actually a juniper. The disease does not kill the plant, but renders the fruit inedible. At this point prune out the cankers and berries during dry weather. It can be prevented by spraying the tree in spring-time with an appropriate fungicide before the disease occurs in the early spring. The disease is always lurking waiting for the right weather conditions to attack the tree. It is also air-borne and can be blown into the landscape on the wind. The best recommendation is to select disease resistant varieties. http://plantdiagnostics.umd.edu/level3.cfm?causeID=1195