American hawthorn rust

Disease

American hawthorn rust

Gymnosporangium globosum (Farl.) Farl.

Distribution: Primarily limited to eastern North America where Juniperus species occur.

Photos

Blisters form on the underside of lesions by midsummer and produce small, tubular projections.

Blisters form on the underside of lesions by midsummer and produce small, tubular projections. Dave Rosenberger, Cornell Univ.
A

Attacks only the leaves (not the fruit) of apple and pear; affects the apple varieties McIntosh and Cortland in particular (A).

  • Crops Affected: apples, pears

    Management

    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.

    Similar Species

    Cedar apple rust is the most common rust on apple; it does not affect pear. Quince rust affects both apple and pear, but is a minor disease on pear. These diseases can be confused with each other, but can be differentiated in part based on the plant tissue infected.

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