Pine-oak Gall Rust

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Filed under Outdoor Notes

May 16, 2010

Pine-oak Rust gall in pine tree

Gall in Pine Tree

Back in April, I found this odd-looking gall on a small pine tree in the eastern part of the County. It is a rust. My first thought was that it might be the highly destructive White Pine Rust, so I asked the District Forester, Mr. Gene Odato, for help.

He was kind enough to identify it as Pine-oak Gall Rust, Cronartium quercuum.

Like many other gall rusts, C. quercuum has two alternate hosts. First it grows on oak; the oak suffers little damage. The rust appears as brown hairlike fruiting bodies (called telia) which produce spores in  late spring or early summer.

Those spores infect the pines, causing these large ugly blisters.

Pine-oak Rust gall

Pine-oak Rust gall

The pines are not so lucky; infections that occur on the main stem of young trees can cause death. Infections on older trees cause weakness in the stem, which may cause the stem to break.

If you find these large, ugly orange swellings on an ornamental pine that you want to keep, I am told that the best thing to do is prune off that branch and burn it.

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