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Cedar Apple Rust

Like many rusts rosaceous trees and Juniperus species are required for the fungus to complete its life cycle. The fungus primarily infects apple/crabapple, eastern redcedar and Rocky Mountain juniper. However, several other Juniperus species are also susceptible to infection, such as J. chinensisJ. horizontalis and J. communis. The most frequently noted symptom of cedar-apple rust is the bright red-orange-yellow spots that develop on apple/crabapple leaves in mid-summer. However, the season’s first symptoms begin much earlier in the spring on Juniperus. Junipers develop 0.25–2” diameter, rounded galls on infected needles and twigs. During prolonged wet periods in the spring, typically from late April to late May, the juniper galls secrete orange-brown gelatinous tendrils.  Pruning of apples and crabapples to promote light and air flow, especially on interior branches, can help to reduce leaf wetness, a prerequisite for infection. Prune dormant galls from junipers during the fall, winter and early spring before the orange-colored spore tendrils are formed.