There are several diseases that can affect your orchids’. Identifying the particular disease on your orchid is necessary to controlling it properly.
This chart shows some of the diseases most often observed on orchids. Read below for more information about each disease and how to eliminate it.
Bacterial Disease
Bacteria Rot
As suggested by the name these bacteria rot is caused by bacteria, mainly Erwinea and Pseudomonas. They mainly affect Phalaenopsis in the warmer months when both temperatures and humidity are high. Bacteria rot often starts as small water-soaked spots on the leaf that quickly develop into fluid filled areas. It can kill an entire plant within a number of days if not addressed quickly. Rot caused by Erwinea will have a particularly foul odor.
To Treat Bacterial Disease
To treat bacteria rot, use a sterile knife and cut the leaf off below the infected area, making sure not to cut through the infected tissue. If the infected area has reached the crown of the plant, it is most likely too late to save it and the plant should be discarded of properly. After removing the diseased tissue it would be wise to spray the infected plant (and those around it) with a bactericide like Physan or SA-20 at the labeled rate.
Fungal Root Diseases
Black Rot
Black Rot is the main fungal rot affecting orchids. Cattleyas seem to be particularly susceptible. Black Rot starts as black spots/lesions on infected tissue and can affect any part of the plant, but usually affects young leaves and shoots. The spots/lesions grow quickly and can rapidly spread throughout the plant.
Fusarium
Fusarium is another fungal disease that affects a wide range of orchids. It mainly enters though the roots affecting the rhizome first before spreading throughout the plant. A tell-tail sign of this pathogen is a distinct purple halo on the outer edges of the rhizome when you cut through it. On Phalaenopsis, early symptoms are observed as yellowing at the very base of the leaves by the stem. This may quickly blacken and the leaves will drop.
Rhizoctonia
Rhizoctonia root rot is mainly associated with old, rotting potting media or damage caused by over-fertilization. It infects the plant roots causing them to go brown and decay.
To Treat Fungal Root Diseases
Treatment involves completely removing the old media from the roots, and well as any dead/decaying root matter, drenching the plant with a systemic fungicide and repotting in clean, fresh media.
Fungal Leaf/Flower Spot Diseases
Botrytis
Tiny black spotting on your orchid flowers is usually a sign of a fungus called Botrytis. It thrives in warm humid conditions with restricted air flow. The tiny spots can enlarge and even cover the entire flower if left untreated. Since the spotting is unsightly, prevention is the best option.
Cercospera
Cerospera causes leaf spotting on orchids and mainly affects Dendrobiums in the hot, humid summer months. Infection usually starts a light yellow circular spotting on the leaves that eventually develop necrotic areas within the spots. The spots quickly enlargen and can cause leaf drop.
Guignardia
Guignardia causes leaf spotting on orchids and is primarily seen on Vandas and Dendrobiums. It starts as small elongated dark-purple spots on the leaves or psuedobulbs . These spots may get larger and eventually may lead to leaf drop.
To Treat Fungal Leaf/Flower Spot Diseases
Effective treatment of fungal leaf spot first requires removal of the infected tissue and reducing leaf moisture, followed by spraying a systemic fungicide. If you have plants that are prone to leaf spot infection, the regular use of a protectant fungicide may be helpful.
In Conclusion
With proper care, many orchid diseases can be avoided.
• Keep your growing area clean
• Water only as needed (& as early in the day as possible)
• Feed regularly at recommended rates
• Space your plants well to make sure they have adequate air circulation
• Use clean and sterilized tools when handling your plants
• Remove and treat plants affected by pests immediately as it’s a lot easier to treat just one plant
Click here to watch our video, “Common Orchid Diseases.”
