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| Cedar-apple rust. J. Schaeffer |
"What IS this thing?" asked Paula on a recent visit to the nature center, as she presented this weird growth. We figured it was some sort of a gall, and we've since learned that it's a gall with a very interesting story.
Galls are unusual plant growths, something like tumors, that are caused by a an insect, bacterium or fungus. The gall that Paula found is caused by cedar-apple rust, a fungus that requires not one, but two, host plants to complete its complex life cycle: an evergreen (typically junipers, cedar or arborvitae), and apple or closely related crab apple.
The fungus over-winters in the gall that the cedar made for it, and with warm spring rains it will swell into a large, orange gelatinous mass with fleshy tentacles from which spores will be released. (Some have said that this phase looks extra-terrestrial, straight out of Star Trek). If the spores land on young, wet apple leaves or fruit, they will develop into yellow and black spots which can damage the leaves and disfigure the fruit. The lesions will eventually produce another kind of spore that will then spread to a cedar again. The whole process takes about two years. The cedar host is usually not damaged significantly, but the rust can cause serious damage to the apple tree and fruit.
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| Black knot fungus. J. Schaeffer |
Another fungal gall is very obvious on many of our native black cherry trees in the park. Black knot fungus causes thick, dark growths on the twigs from which emerge wind-borne spores. These growths can interfere with the movement of water and nutrients up from the roots and sugars down from the leaves, killing the twig or causing poor growth of the tree.
Fascinating fungi--an interesting group of organisms. Be glad athlete's foot just itches and doesn't make a gall!
