Phomopsis gall on hickory

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There are at least 232 species of the fungus Phomopsis. Several of these produce abnormal swellings (galls) on bitternut hickory trees. The galls are identical in appearance and identification of the associated species in the field is not possible.

Galls may occur singly or in clusters on the trunk and branches. They are woody, rough, more or less round swellings. They can be from very small to 10″ in diameter. They appear as tight clusters of nodules, each nodule up to 1″ or more in diameter. If cut open they reveal disorganized woody tissue but no insect chambers or tunnels.

Spores are produced throughout the growing season and are spread by wind and rain splashes. It is believed that spores infect a host by entering a wound of a young twig. The fungus then spreads to branches and to the trunk. The galls do not kill the host but reduce vigor and girdle small branches causing dieback. Uninfected trees may occur near heavily infected ones.

Bitternut hickory

Year-round

Sources: 7, 24, 30.

Many of the trees around this Bitternut Hickory, pictured were infested with this fungus.

Infestation

Gall

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Location: Grey Cloud Dune SNA, Cottage Grove. On riverside of rail tracks

Many of the trees around this Bitternut Hickory, pictured were infested with this fungus.