These rust diseases can be very harmful to the thriftiness of apple trees. If severe infections of cedar-apple rust continue for several seasons, apple tree death can be the result. Damage to apple is brought about chiefly by premature defoliation.
Affected fruit are smaller, deformed, and undesirable for marketing.
On the native red cedar and ornamental cedar, Juniperus spp. Cedar tree showing abundant cedar-apple rust galls. On the under side of the leaf, lesions are formed called aecia. At the point where an aecium is formed, hairlike projections can be observed. The leaf thickens around these projections, causing the aecium to have a cuplike appearance.