Alternate hosts include hawthorn, mountain ash, apple, and crabapple. When infected, the upper sides of leaves have orange-yellow spots that are surrounded by red bands. The lower sides of the leaves have cup-like lesions that produce spores that can infect the junipers and cedars. Infection of the deciduous alternate hosts can cause premature defoliation. The defoliation causes additional stress upon the infected trees, making it more susceptible to insect and disease problems.
Cultural practices can help control the spread of cedar-apple rust.
Pruning the galls prevents new spore horns from emerging. The pruning should be done in the late winter or spring. When designing a landscape, select rust resistant varieties of hawthorns, mountain ash, apples, and crabapples. Place these alternate hosts as far as possible from the primary hosts. Crabapples and other alternate host trees can also have a protective spray applied in the spring before flowering and continue spraying until the spore horns on the juniper become inactive.