Cedar Apple Rust Cedar Apple Rust Cedar-apple rust is a disease that causes substantial injury to apple, crabapple and hawthorn trees in Nebraska.
Trees severely defoliated by the disease are a common site in late summer.
Infection of trees, by the fungal spores that cause the disease, begins when the flower blossoms are pink but before they have opened, usually May and June. The fungal spores are released at this time by their alternate host, juniper. The spores are blown by wind to susceptible apple trees and soon leaf spots develop. The spots may have a band of red or yellow around them depending on the tree's susceptibility to the fungus. Fruit symptoms are similar to leaf symptoms.