Phomopsis Galls
At this time of year, when leaves are rapidly falling off deciduous trees, it is easy to spot clusters of woody galls on the branches and trunks of Bitternut Hickory, Red Oak and maple trees, among others. These abnormal, woody growths known as Phomopsis galls are caused by a fungus in the genus Phomopsis. They begin to form as patches of rough bark, and when fully formed they range from the size of a pea up to the size of a basketball.
Spores are produced by the fungus throughout the summer and are spread by wind and rain splashes. It is thought that spores infect a host by entering a wound in a young twig. The fungus then spreads to the branches and trunk. The galls do not kill the host tree, but can girdle small branches causing dieback. Many affected trees live for decades. (Photo: Bitternut Hickory tree infested with Phomopsis galls.)
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