Xyella Fastidiosa, a scorch disease in trees
By Susan Sims Sims Tree Health Specialists
Oleander leaf scorch that has decimated large quantities of oleanders was identified September 1995 in Rancho Mirage, CA. Dr. Stoner of Cal Poly Pomona knew “something was going on with Oleanders in the Palm Springs area” long before Sims was called to Rancho Mirage. Remembering Dr. Stoners words Sims brought Marcia Greybus, at that time a new pathologist with UCR. Others contacted at the same time were Mike Henry, UC cooperative extension, and Dr. Fred Roth, of Cal Poly, Pomona. Sims, Marcia Greybus and Mike Henry teamed up to collect and investigate the desert Oleander problem. Scorch was found and both Marcia and Fred made identical identification of the bacteria Xyella Fastidiosa.
Soon the bacteria spread to the freeway oleanders from Palm Springs to San Bernardino, Riverside, Orange, LA counties and the disease continues to spread. The primary vector are sucking insects particularly the glassy winged sharpshooter, Homalodisca coagulata.
The disease expresses itself in Oleanders by scorching the leaf tips, then margins and finally causing the dieback of branches to the ground. The bacteria infest the Xylem tissue, water transport system, clogging or blocking the water flow. On days that are hot or dry, sufficient water cannot reach the leaf tissue causing scorching and dieback of leaf and branch tissue.
A different strain of Xyella fastidiosa is responsible for Pierce’s disease in grapes. Currently it can be found in backyard grapes in Riverside County. In 1892 50,000 – 60,000 acres of grapes were lost in Orange County to Anaheim’s disease. Later Xyella fastidiosa would be discovered as the pathogen.
Sims’ has been following the spread of Xyella. Sims and Ferrin have been testing symptomatic trees finding Xyella in various ornamentals. Liquidambar seems to be the hardest hit tree so far. Olive trees are affected but stress such as heavy pruning or relocation is important in the incidence of Xyella. Following is a list of other ornamentals found with Xyella. We found Xyella in avocado last November but were unable to reproduce it in spring.
Currently a cure is unknown. Bactericides applied strong enough to kill the Xyella also will kill plant tissue. Sims is researching holistic and elemental treatments. The most promising requires treatments prior to disease that builds the plants immune system.
