Bacterial orchid diseases are ones that come up at least one or two times while growing plants if you’re an experienced gardener, they are worrying if you don’t tackle them. Green thumbs, on the other hand, might find it difficult to identify the symptoms of these bacterial diseases in orchids correctly, more so, treating the infection and controlling the spread.Bacterial Orchid Diseases

Unlike fungal diseases, bacterial infections move quickly through orchids, causing the plant to die if action isn’t taken immediately. In this guide, we’ll explore the bacterial diseases of orchids, their causes, treatment, and prevention methods.

List of Bacterial Orchid Diseases

1. Bacterial Brown SpotBacterial Brown Spot Orchid Disease

Symptoms of Infection
  • Brown, water-soaked spots with green margins
  • Oval spots with a necrotic center
  • Dark, foul-smelling liquid from infected spots
  • Wounds or openings on the plant’s surface, especially after using contaminated gardening tools
  • Plant stress due to insufficient nutrients, inappropriate watering, or inadequate humidity
  • Improper plant hygiene and warm conditions
  • Remove and destroy infected plant parts with a bactericide or copper fungicide
  • Improve air movement around the orchids and reduce leaf wetness
Prevention Methods
  • Avoid overhead watering and the use of unsterilized tools
  • Maintain proper plant hygiene
  • Sterilize tools and materials before using them on orchids

The bacterial brown spot is a common orchid disease caused by Acidovorax avenae subsp. cattleyae but primarily affects phalaenopsis orchids. The infection mainly enters the orchids through wounds on their leaves but can also infect the stomata of seedlings.

Using contaminated tools without sterilizing them first can also lead to infection. The pathogen also thrives in humid conditions under warm temperatures ranging from 54 to 68 degrees Fahrenheit.

Brown spot starts as small, brown, water-soaked lesions with green margins on orchids before becoming large and necrotic, while the green margins become yellow and with this signature feature you can easily tell them.

On some orchids, necrotic spots produce a dark, unpleasant liquid, and seed pods become aborted and dormant. Severely infected leaves become brittle and begin to wilt or drop.

There isn’t yet a cure for bacterial brown spots, so the only thing you can do to save your orchids is to try to control the disease to prevent it from spreading, and so; you must prune away diseased parts with sterile scissors and spray the plant with a bactericide.

In addition, you must take further steps to prevent the bacterium from infecting other plants by improving air circulation, sterilizing all tools with rubbing alcohol or bleach before use, avoiding overhead watering, and maintaining proper plant hygiene always.

2. Bacterial Soft RotBacterial Soft Rot Sickness of Plants

Symptoms of Infection
  • Initial, small, soft rots on one or more leaves
  • Circular or oval, brown rots eventually become dark brown or black
  • Sunken lesions with definite margins
  • Contamination through tools or insects
  • Overcrowding of pants and poor airflow
  • High temperature and excess moisture or humidity
  • Apply a bactericide once symptoms begin to show
  • Isolate the plant and cut away infected parts using a sterilized tool
Prevention Methods
  • Maintain good sanitation and avoid overhead watering of orchid leaves
  • Disinfect all gardening equipment with bleach or alcohol before use
  • Ensure proper air movement around plants

Bacterial soft rot is caused by many types of bacteria, such as Dickeya dadantii, Pectobacterium carotovorum, and certain Pseudomonas, Bacillus, and Clostridium species.

These bacteria can enter orchids through wounds or spread from an infected plant when grouped or through insects and tools. It can also be spread when contaminated water or soil is used, and they would multiply and increase.

Initial symptoms are small, oval, or round, water-soaked spots on orchid leaves before becoming black or brown. These spots eventually enlarge, becoming sunken and soft, while tissues beneath the spots become mushy with black or cream-colored discoloration.

Just like other diseases that spread, this also has a further spread of these pathogens, causing infected spots to produce a foul odor due to the disintegration of plant tissues. In addition, you must also consider that there are no treatments for soft rot if it has taken over completely.

Once your orchids develop symptoms of this disease, isolate the plant immediately and remove dead or infected tissues. Ensure you dispose of them properly as opposed to composting them, and after this, you can begin treatment with a bactericide, and make sure that it wouldn’t repeat.

To prevent your orchids from developing soft rot, ensure your plants are well-spaced to allow proper airflow and grown in well-draining soil to prevent moisture build-up. Also, avoid overhead irrigation and keep the growing area sanitary; this way, you will take the right measures.

3. Pseudomonas Leaf SpotPseudomonas Leaf Spot Disease of Orchids

Symptoms of Infection
  • Small, dirty-green, water-soaked lesions on orchid leaves and stems
  • Lesions become necrotic and turn brown or black with yellow margins
  • Leaves dry up and may begin to drop
  • Use of contaminated tools or materials. Infection through rain, insects, or wind
  • Use of contaminated soil to grow orchids
  • Warm, humid conditions
  • Isolate infected plants and prune away infected parts with a sterilized tool
  • Spray the plant with a copper-based fungicide
  • Use beneficial bacteria or fungi to suppress the spread of the disease
Prevention Methods
  • Maintain good plant hygiene and sanitation
  • Provide better airflow and reduce moisture
  • Properly fertilize the orchids to improve their disease resistance

Pseudomonas Leaf Spot is an orchid disease caused by various species of the bacteria Pseudomonas, such as Pseudomonas cichorii, Pseudomonas aeruginosa, or Pseudomonas savastanoi. This is a disease that would take plants in different ways, and they may harm the leaf, specifically.

Symptoms of this disease can vary depending on the species of the disease and the orchid. However, general symptoms include small, dirty-green, or black water-soaked lesions blights that turn black or brown with yellow margins as the disease progresses. Eventually, the leaves wilt and drop off the orchid.

Pseudomonas leaf spot thrives in favorable conditions, including warm temperatures and high humidity. They take root in the soil or plant debris for about six months before colonizing the orchid; as they grow, they start to enter through wounds and openings caused by harsh weather, insets, or damage during pruning or propagation.

They can also be transmitted via rain, seeds, wind, using contaminated tools and water, or by practicing overhead irrigation. This means that they can come in different ways, as some may be ones that you didn’t consider or have in mind.

Orchids infected with Pseudomonas leaf spots can be treated using a copper-based fungicide after being isolated, and the diseased parts are removed and disposed of. You can also use beneficial fungi or bacteria to control the spread of the disease, and it would reduce the risk of fully being contaminated.

Be sure to adhere to the instructions on the label of the copper fungicide to avoid using it in excess and damaging your orchids.

4. Xanthomonas Leaf SpotXanthomonas Leaf Spot Illness for Orchids

Symptoms of Infection
  • Necrotic, water-soaked, gray spots on the undersides of leaves
  • Small, yellow, or tan, angular spots around leaf veins
  • Brown, V-shaped necrotic lesions towards the petiole
  • Use of contaminated tools and equipment
  • Natural wounds, cuts, or openings on leaf surfaces
  • Contamination through wind, insects, or rain
  • Remove and dispose of infected plant parts properly
  • Spray the plant and surrounding orchids with a copper-based fungicide
Prevention Methods
  • Avoid overhead irrigation to avoid wetting the foliage
  • Proper plant spacing to allow air circulation
  • Quarantine new plants before placing them with the orchid population

Xanthomonas Leaf Spot infects orchids causing dull-gray water-soaked spots on the undersides of the leaves initially. This disease is caused by the Xanthomonas campestris pv. zinniae bacterium, often spread through contaminated plant material as they can live in them for up to many months before manifesting. The disease can also be spread by insects or using contaminated garden equipment.

Xanthomonas thrives in warm temperatures. Hence, orchids native to tropical forests are more susceptible. Symptoms of this disease are often confused with symptoms of Pseudomonas due to the leaf spots.

However, you should take note of the shape of the spots, as when Xanthomonas progresses, the orchid leaves develop angular, tan, or yellow spots and can have brown, necrotic lesions around the petiole.

Like other bacterial orchid infections, Xanthomonas has no cure, so the best you can do is prevent it from spreading. Remove diseased parts of infected plants and dispose of them properly, and remember to sterilize your tools before use and in between each cut. Then, you can go ahead and treat the plant with a bactericide or copper-based fungicide.

To prevent Xanthomonas from infecting your orchids, ensure you use disease-free seeds and plant materials to grow your plants. Treat your seeds in hot water or a bleach solution for about 30 minutes.

New plants should also be quarantined for about a month before introducing them to others. Avoid overhead irrigation and practice good hygiene around your plants.

5. Black RotBlack Rot Bacterial Disease of Orchids

Symptoms of Infection
  • Black, water-soaked, V-shaped lesions on leaves, flowers, and stems of orchids
  • Lesions exude a dark liquid when squeezed or pressed
  • Leaf veins may become brown or black
  • Inadequate growing conditions and poor sanitation
  • Excess moisture due to overwatering or high humidity
  • Contamination through wounds and cuts on leaves
  • Cut out infected parts of the orchid using a sterile knife or scissors
  • Apply a copper fungicide or bactericide
Prevention Methods
  • Sterilize all plant materials and tools before use
  • Avoid leaving your orchids wet for a long time, especially the crown
  • Use a high-calcium fertilizer to strengthen new growth and prevent the growth of the bacteria

Black rot is caused by Erwinia carotovora bacteria, showing up as black, water-soaked spots on different parts of the orchid. Cattleyas are most susceptible to this disease, but Paphiopedilum, Phalaenopsis, and Miltonia are also prone, especially with excess moisture or high humidity. As the spots spread, they enlarge to cover the whole leaf and sometimes the pseudobulb, producing a dark fluid when disturbed.

Black rot can be transmitted from one orchid to another when infected ones are grouped with healthy ones or when infected tools are used. It can also be spread via insects, wind, or water and enter through wounds on the orchid’s leaves, and the damage would be worrying if it comes in and spreads further.

Diseased plants should be isolated immediately after infection symptoms to control the spread. Prune away infected parts using sterilized scissors or shears and dispose of them appropriately. Apply a bactericide to the plant and others in the growing area.

6. Halo BlightHalo Blight Disease of Plants

Symptoms of Infection
  • Yellow-green halos around water-soaked lesions on leaves
  • Lesions may turn brown and become necrotic
  • Leaves might begin to wilt and drop
  • Use of contaminated water or tools
  • Improper sanitation around orchids
  • High humidity with poor airflow
  • Remove infected tissue and dispose of it properly
  • Spray with a copper-based fungicide or bactericide
Prevention Methods
  • Avoid overhead irrigation and reusing irrigation water
  • Always allow adequate air circulation around orchids
  • Keep the growing area sanitary at all times

Pseudomonas syringae pv causes halo blight. phaseolicola that enters plants through wounds ad thrives in cool temperatures, unlike other types of bacteria. The disease causes small, water-soaked spots on leaves that turn a dark brown with a greenish-yellow halo around it.

However, unlike other bacterial orchid infections, the necrotic center does not expand. Occasionally, the spots can exude a slimy, translucent liquid. With systemic infections, younger leaves become chlorotic and wilt. Using dirty soil or bringing healthy orchids into contact with infected plant debris can spread Halo blight.

The orchids can stay infected for a long time before they start to show symptoms. Thi sis why once you notice symptoms, isolate the plant, remove and dispose of infected parts, and treat it with a copper fungicide or bactericide before introducing it back into the growing area.


With so much information to take in, let’s quickly run through some essential points to have at your fingertips:

  • There is no cure for these orchid bacterial diseases, so it is best to prevent them from the onset.
  • Bactericides or copper fungicides are best used to treat these infections.
  • Water-soaked lesions on the leaves characterize bacterial diseases.
  • Be careful and try to tackle the issue in the beginning phase so that it doesn’t spread so much.

Now that you know the symptoms of bacterial orchid diseases, you can easily identify them on your orchids and start treating them immediately.

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