Gymnosporangium clavipes (Cooke & Peck) Cooke & Peck in Peck
Attacks only the fruit (not the leaves) of apple and pear. Symptoms begin as a purplish lesion, usually appearing on the calyx end of the fruit. As the disease progresses, the entire calyx end becomes blistered and deformed. Tube-like structures eventually form and produce powdery, bright orange spores (A).
Primarily limited to eastern North America where Juniperus species occur. Quince rust affects both apple and pear, but is a minor disease on pear.
Cedar apple rust is the most common rust on apple; it does not affect pear. Hawthorn rust affects the leaves of both apple and pear. These diseases can be confused with each other, but can be differentiated in part based on the plant tissue infected.
Eliminating red cedar trees in the vicinity of orchards helps to reduce disease pressure. However, it is difficult to remove all sources of disease because the infective spores can travel on air currents for several miles. Pruning the "cedar apples" from cedar trees is an alternative to removing the tree itself. Where the disease is a problem, fungicides are applied from tight cluster through petal fall. The varieties Cortland, Crispin, Golden Delicious and Jonagold and are susceptible to both cedar apple and quince rust, Ida Red and Paula Red are susceptible to cedar apple rust, and Delicious and Empire are susceptible to quince rust.
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