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.
|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
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.
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.
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.
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.
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
• 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)
• 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
• 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
• 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