my 3 year old howthorn has some blight
Your hawthorne has a rust disease. 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. Other pomaceous hosts may include serviceberry, apple, crabapple trees, etc.The most common alternate host in this area is the Eastern Red Cedar which is actually a juniper.
It can be prevented by spraying the tree in spring-time with an appropriate fungicide before the disease occurs in the early spring. In general, fungicides are preventatives, not curatives. They only protect new or uninfected foliage. 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. You do not have to spray. The best recommendation is to select disease resistant varieties. http://extension.umd.edu/hgic/rust-diseases-trees-and-shrubs