Cedar Apple Rust

A client in Collegeville asked me to look at her apple trees, which appeared unhealthy as the leaves were turning color and dropping off.

Viewed up close, the leaves display the orange colored lesions typical of cedar apple rust.


Nearby, at the property line, is an Eastern red cedar tree that is completely infested with cedar apple rust galls.

This is an interesting disease because it has a two year life cycle – spores (aeciospores) released in summer from the fungal fruiting bodies on the apple leaves travel through the air and when they land on Eastern red cedar or another susceptible juniper infect that host and produce galls that, in the spring, produce spores (basidiospores) that, in turn, infect leaves of nearby apple trees.  To see the fruiting galls on juniper in spring (an incredible sight!) scroll to the April 21 entry in this column.

I also noticed evidence of a canker fungus disease (possibly Botrosphaeria) and fireblight, a disease caused by a bacteria – Erwinia amylovora – both causing injury and death of branches.

If my client can convince her neighbor to remove the cedar tree (it is not a nice tree, either location or health-wise_ her apple trees will probably have much less leaf-spot problems in future years.

This winter we will do maintenance pruning on the apple trees, including removing the dead wood.  This should reduce the problem with the Botrosphaeria and Erwinia diseases.

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