Q. I live 8 miles northeast of Mesquite NV in Littlefield
Arizona. I'm sending two pictures of some scaly growth like woody galls on the
tips of my Oleander branches. There is also galling taking place on the
branches and leaves. My oleanders are the only ones infected. How do I correct
this problem? Will it kill the plants? Every plant is infected, about 300.
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| Oleander gall from the reader |
A. This is called oleander gall in Arizona, oleander knot
in California and Texas calls it bacterial gall. I wouldn't use any chemicals. Prune it out and sterilize pruners after cutting because
it will spread on pruning instruments. If you use bleach as a disinfectant make
sure you oil any steel that it comes in contact with.
This particular disease is spread from plant to plant on
pruning tools. It can also be spread during wet, windy weather just after
pruning. Avoid irrigating oleander with overhead sprinklers. Drip irrigation or
bubblers would be a better choice.
Even though
it’s a bacterial disease, you can use chemicals such as copper fungicides to
help reduce the infection but they are not necessary. Most of this can be
handled with proper pruning.
Make
sure all pruning equipment is sanitized. In this particular case, you should
sanitize pruning tools between cuts and between plants to keep from spreading
this disease on pruning tools.
I would
use a 10% bleach solution applied to pruning blades or pruning saw with a spray
bottle. Make sure you oil all pruning tools and blades when finished or the
bleach will rust them.
Plants
that have a few of these galls present can be pruned and the galls removed.
Prune 6 to 10 inches below the galls and sanitize your pruning equipment before
each new cut.
If a plant
is severely infested with oleander gall, I would cut it to the ground this
winter and let it regrow from the base.
Fertilize
the plants with a high nitrogen and high phosphorus fertilizer in January and
give them a large volume of water each time you irrigate.
Oleander Galls in the Low Desert
PLANTS MOST SUSCEPTIBLE: Oleander
SYMPTOMS:
Rough, fissured growths on twigs, branches, leaves,
flowers, and seedpods, often appearing in chains. Galls start out as small
bumps and grow into wart-like growths generally between 1/2 to 1 inch in
diameter. Large galls may actually be several small galls that have grown
together.
CAUSES:
These galls are the result of growth of the bacteria
Pseudomonas syringae inside the plant. The bacteria can enter the plant through
wounds caused by pruning, frost damage or other injury or through natural openings
in the leaf, blossom and stem. Water can carry the bacteria from diseased
plants to healthy ones in the splash from rain or sprinklers. The bacteria is
also moved from infected plants to healthy ones by unsuspecting gardeners on
their pruning tools.
MANAGEMENT:
Prevention: Inspect oleanders carefully prior to
purchase, do not buy plants that have galls.
Management: Remove the galls by pruning several inches
below. Treat each cut with 10% bleach solution. Dip pruning tools in a 10%
bleach solution between EACH cut to reduce the possibility of spreading the
bacteria. Bag and discard cuttings. Do not compost diseased plant material.
Prune during the dry seasons to avoid infection of
wounds. Avoid sprinkler irrigation while pruning wounds are fresh.
Severe infection of large shrubs is difficult to control
by selective pruning. Even if you cut down the entire shrub, the new succulent
growth will still be extremely susceptible to infection. In certain situations,
removal of the diseased plant and replanting may be the best method of control.
Oleander knot—Pseudomonas savastanoi pv. nerii
Pseudomonas savastanoi pv. nerii causes galls or knots on
oleander stems, bark, and leaves. Twigs and branches can die back, but the
overall plant health is usually not seriously threatened. Gall bacteria
reproduce in fissured or galled bark and are spread by contaminated water,
implements, or hands. Healthy tissue is infected through fresh wounds during
wet weather. Susceptible wounds include frost cracks and any leaf scars on
branches.
Solutions
Avoid overhead watering. Prune out and dispose of
infected tissue during the dry season. To prevent spreading pathogens on
infected tools, clean tools of debris after each use and thoroughly spray them
with disinfectant or soak them in disinfectant for one or more minutes. Tools
can be sterilized using a commercial disinfectant as directed on the product
label. Homeowners on their private property can use household bleach or
disinfectant cleaners diluted 1 part disinfectant to 10 parts water.
Bacterial gall
Disease Pathogen Name: Pseudomonas syringae pv.
savastanoi
Pathogen Type: Bacterium
Period of Primary Occurrence: after spring rains &
cool weather
• The bacterium must have a wound site to enter the
plant, and cold weather injury in early
spring after a rain is a common circumstance under which
infection takes place
• Most common after a cool wet spring
Description / Symptoms
• The bacterium is systemic in the plant, and causes
galls to form on flowers and stems
• Leaves also become galled
• Twigs and branches can die back, but overall plant
health is usually not seriously
threatened
• Gall bacteria reproduce in fissured or galled bark and
are spread by contaminated water,
implements, or hands
• Healthy tissue is infected through fresh wounds during
wet weather
Best Management Practices (BMP)
NON-CHEMICAL CONTROL
• Bacterial gall normally will not kill the plant
• Infected plant parts can be pruned, but care should be
taken not to disseminate the
bacterium on pruning tools
• Prune infected tissue well below the infection site, at
least a foot if possible, and disinfect
pruners between cuts by dipping them in a 10% bleach
solution (common household
bleach at 1:10 dilution) for a few seconds
• Be sure to rinse the bleach off tools when you are finished
and apply an oil lubricant to
avoid corrosion of the metal
CHEMICAL CONTROL
• Severe infections can be controlled by applying
Bordeaux mixture or a copper fungicide
beginning in the fall and periodically spraying through
the spring as new growth
appears
• Bordeaux mixture (originated in France) as a 4-4-50
ratio. For a small amount of mixture,
the ingredients are:
- 3 1/3 tablespoons of copper sulfate and 3 tablespoons
of hydrated lime, mixed in
one gallon of water
- The mixture will turn the tree blue; however, the color
will eventually disappear.
Caution must be taken NOT to store a mixture of Bordeaux
- The ingredients must be kept separate and custom-mixed
as a fresh spray
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