I've been noticing silver cholla with unusually large tubercles in various parts of the desert, but especially along the Alamo Road corridor on Desert NWR. After recently rephotographing several cactus along Alamo Road, I've confirmed my suspicions that these cactus are diseased. The disease seems to cause a generalized "swelling" of the stem segments and tubercles, after which the stem segments turn white, die, and become powdery. It would be interesting to have a plant pathologist chime in here.