Identify rust on Ornamental Apples
We have several ornamental apple trees in our yard. For several years, some apples have developed a rust colored fur on the apples. It does not seem to harm the trees as they are growing bigger every year. But, this year is particularly heavy and the dust from this disease is all over our outdoor furniture & patio. Is this harmful to pets or humans? Is there a non-toxic way to treat this problem? Pictures below. Thank you.
Dakota County Minnesota
It looks like your tree is infected with one of the gymnosporangium rust diseases. These diseases require two hosts, one from the Rosaecae family (crabapple in your case), and one from the Cupressaceae family (cedar or juniper), in order to complete their life cycle. They will show different symptoms on the alternate hosts. The fact sheet below will give a detailed discussion and controls. One obvious control is to remove one of the alternate hosts. Read here: