I was captivated by these trees, which have a mystical, storybook quality.
This spirit tree appears to have flowing hair. It spreads its arms and blesses the world.
However, this many-eyed tree is a quiet observer.
What do you see? I see an old man’s face growing from this tree, although the tree itself is young.
Of course, I’m looking through the eyes of an artist and storyteller. An arborist sees only the cancer.
This tree has been infected by Rhizobium radiobacter, formerly known as Agrobacterium tumefacians. Rhizobium is a rod-shaped bacteria that lives in soil or within infected plants. It enters young trees wounded by chewing insects, storms, frost, gardening equipment, etc.
Once inside the plant, the bacteria inserts its own DNA into the cells of its host. The plant responds by over-producing chemicals that feed Rhizobium. Within four weeks of infection, a tumor, or gall, appears at the infection site. At first it is lightly colored and spongy, but as it continues to grow it darkens and hardens. It may also produce secondary tumors.
When the tree is no longer able to meet the demands of the bacterial colony, the gall stops growing. As it decays, it releases bacteria into the soil, where Rhizobium can live for years. Water carries the bacteria to new locations. It can also be transported on the feet of humans, animals, and chewing insects.
Although oak trees are particularly susceptible to Rhizobium radiobacter, a wide variety of woody plants can also be infected.
REFERENCES
Insect Galls: The Good, the Bad, and the Ugly. UF/IFAS Univesity of Florida.
Galls. 4-H Forest Resources.
Galls on Plants. Insect Diagnostic Laboratory, Cornell University.
Key Diseases of Oaks in the Landscape. University of Georgia Extension.
Bonkowski, John, Joseph, Bacheline, Bayo, Deanna. Agrobacterium tumefaciens. University of Florida, BugwoodWiki.
Moore, L.W., Crown Gall Disease of Nursery Crops. Pacific Northwest Pest Management Handbooks.
Watt, Bruce. Crown Gall. The University of Maine Cooperative Extension.
Crown Gall. University of Minnesota Extension.
