|QUESTION: Three years ago I planted 50 oleanders,
both white & red, in my garden in Napa, California. We have
been advised that most of these plants now have a "canker"
primarily in twig formations, and that this disease is fatal, that
there is no cure. And that we can cut out the canker, but the plants
will probably only live another three years, no matter what we do.
Can you confirm the above, or do you know of a possible remedy that
will save these plants?
ANSWER: The most likely problem is Nerium canker,
caused by a bacterium, Pseudomonas syringae pathovar savastanoi.
Galls and lesions may damage stems, flower parts, seed pods, peduncles,
and young leaves. Mature galls on stems are 1-2 cm in diameter.
Galls on succulent twigs may appear cankerous because the tissues
first infected die, and the stem may split at that point. Leaves,
flowers, and seed pods develop wart-like galls and become distorted.
The seed pods may be twisted and stunted. Only fresh wounds are
suitable infection courts. Wounds include leaf scars (susceptible
for a few days), damage from pets, children and workers, high
wind, and pruning cuts. In areas with distinct wet and dry seasons,
nearly all infection occurs during the wet season - approximately
October to May in California. Control efforts may be only moderately
effective. Do not allow a sprinkler irrigation system to wet the
leaves (mulch and use drip irrigation if necessary). On some fruit
trees, there is evidence that a bed of mulch releases yeast spores
that compete with plant pathogens on plant surfaces. By all means,
do not work with plants when leaves are wet because you can carry
epiphytic (surface growing, not yet infecting the leaves or plant
parts) bacteria to other plants and introduce them into unnoticeable
leaf wounds. Minimize worker, children, and pet activity in the
vicinity to minimize wounding. Minimize or avoid nitrogen fertilizer
in the vicinity because an excess of Nitrogen leads to tender
succulent growth that is probably more susceptible to this bacterium.
Another possibility is an anthracnose disease canker, caused
by a fungus, Gloeosporium. It may be seen on branch tips, especially
after freeze injury, environmental stress, improper nutrition,
or natural senescence; or along branches. Control suggestions
include sanitation pruning to remove dead and diseased twigs,
avoiding overhead irrigation (sprinkler system) because leaf wetness
allows the fungus to infect new wood and to splash spores from
diseased wood to healthy wood.
MARK BLACK, EXTENSION PLANT PATHOLOGIST adds:
I would add one more disease for South Texas. The question I
answered earlier was directed primarily at the Napa, CA area and
also based on their description of stem cankers. The Texas' question
is probably for a different symptom: leaf scorch and severe limb
dieback, and even plant death.
Larry Barnes, Plant Pathologist in College Station (and workers
in California also) have positive serology tests from oleander
with scorch and dieback for Xylella fastidiosa, a xylem limited
bacterium vectored by plant hoppers. If this sounds familiar,
this is the same name used for the Pierces Disease pathogen in
grapes. The bacteriologist tell me that the grape "strain"
is different from the numerous strains that get in a lot of woody
plants, and that
X. fastidiosa in trees does not infect grape. I would consider
this disease in oleander non-treatable. There have been experimental
injections with antibiotic that improved symptoms (I think the
host plant was a shade tree), but symptoms developed again after
a period of time. This was one piece of evidence that the disease
was caused by a bacterium. There is no label for this use of antibiotics,
and it would be impractical on multiple trunk species like oleander,
and probably even impractical on single trunk trees. I have seen
symptoms that fit this on oleander in Kinney and Uvalde Counties
I recommend replacing affected oleanders with a native such as
TX. Mountain laurel, evergreen sumac, or cenizo.
HERE IS AN ARTICLE WRITTEN ABOUT THE PROBLEM IN CALIFORNIA:
California's oleanders devastated by disease
Text by DON DALE
In what could signal a huge economic loss, the advent of oleander
scorch in the Los Angeles area may cost growers their entire oleander
inventory. The disease, also called oleander leaf scorch, showed
up in the Palm Springs, CA, area in approximately 1990 and has
since spread to Los Angeles and Orange counties. It is caused
by Xylella fastidiosa--the same bacteria implicated in Pierce's
disease, which has long plagued the wine industry and is vectored
by the glassy-winged sharpshooter (Homalodisca coagulata). The
insect pest is native to the South and serves as a vector when
it feeds on the xylem sap from one plant and transfers it to another.
There is currently a quarantine on nursery stock leaving Los
Angeles County in order to ensure no glassy-winged sharpshooters
are being shipped to other parts of the state. Species are inspected
at both the shipping nursery and the destination, and even one
sharpshooter egg mass can cause plant rejection.
According to Dr. Jerrold Turney, the Los Angeles County plant
pathologist, these inspections have become a tremendous problem
for nurseries because although oleander scorch may not currently
affect a wide variety of plant species, there are some 200 hosts
listed for glassy-winged sharpshooter. 'It's a very expensive
program for the nurseries," the expert added, and there are
high costs associated with chemically treating nursery stock against
this insect pest.
The sharpshooter is active year-round in much of warm Southern
California, and in that part of the state masses of oleanders
are dying from this bacterial disease. "There's no treatment.
It's fatal," explained Turney. According to the plant pathologist,
leaves of infected plants turn grayish green and wilt; they do
not respond to watering, as is the case with some instances of
wilting. Then, in a period of one to two months, foliage begins
to turn brown. "Then another branch will become symptomatic,"
Oleander scorch gets progressively worse, eventually killing
the plant. It may take some time for the entire plant
to become infected, and death typically occurs between one and
three years after initial infection. 'This bacteria is native
and occurs throughout the United States," Turney noted, though
the professional hasn't heard of any oleander die-off in other
parts of the country.
Oddly enough, the same species of bacteria also affects grapes;
however, if the bacterial isolates from grapes are
placed on oleanders, they will not infect the plants with scorch.
The reverse is also true. And although the disease can be controlled
in the wine industry by encouraging growers to select resistant
rootstock, there is no similar option available to nursery professionals
who grow oleanders or other susceptible species. X. fastidiosa
samples taken from different plant species are called "pathovars,"
because they can't be distinguished from each other by species
(bacteria identification is problematical) but can be identified
by the plants they infect.
The financial loss sustained by nursery professionals could be
enormous, Turney said. Already, oleanders are dying along some
California freeways, where the plants are staples of the landscape.
The expert estimated the California Department of Transportation
has planted 25 million oleanders in the southern part of the state,
and their loss would require a significant outlay for removal
and replacement. 'I think in the next 10 years we'll lose the
vast majority of our oleanders," Turney predicted. A very
real fear, he said, is that X. fastidiosa will ultimately infect
other plants. In that case, other species could go the way of
According to Turney, the bacteria also causes almond scorch,
alfalfa dwarf and peach stunt, among other diseases. It currently
is showing up on - and killing - olive, sweet gum and purple-leaved
plum trees in California's Riverside County.
For more information, visit the University of California's Cooperative
Extension's Web site at: www.ipm.ucdavis.edulindex.html