A sac fungus, Taphrina prunisubcordata, induces “plum pockets” or “plum bladders” in Sierra plums (Prunus subcordata). The infected fruits expand and elongate into large, soft, light green, hollow “bags” that are round or potato shaped. The plum pocket surfaces are furrowed and covered with a waxy bloom. As the plum pockets age they turn beige then brown and dry out.
Sac fungi form their spores in microscopic sacs. In the late spring or early summer the spores are forcibly discharged. Wind carries the spores to new hosts. All fruit that is infected is killed, but T. prunisubcordata does not eradicate all plums on any single Sierra plum tree.
Plum pocket gall fungus is found from the Rocky Mountains west throughout the Pacific States.
More information on the host, Sierra plum, can be found in my previous post. (See “Sierra Plum” on 09-27-17).
The pocket gall specimens were collected along Modoc Forest Road 40N04 near Spring Creek in May. I photographed the dried pocket gall along the Headwaters Trail in Burney Falls State Park in June. This was a gall from the previous season. Both locations are in Shasta County CA.