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Presented by Marilyn H. S. Light Wed Feb 11, 2004 |
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Your plant has an ailment, a pest or disease problem or both, and you have to decide what to do. This may be your one and only plant, a real favorite, or one that you recently purchased for a considerable sum. There may be many plants showing the same symptoms. You justifiably have that sinking feeling.
1 - What is the specific name of the disease? Diseases have many common names yet may be caused by a variety of organisms producing much the same symptoms. Since disease control measures are often specific to a particular organism, it is important to know what you are dealing with. Ask about the scientific name of the organism. 2 - How certain is the diagnosis? A plant disease affecting commercial crops is never diagnosed on the basis of a single test but for some of the common ailments affecting hobbyist orchid collections, knowing the host plant, the symptoms, where it is being grown and under what conditions, and what the disease organism looks like (bacteria, spores, etc), can serve the purpose. Here we see bacteria, some of which clearly moved (swam) during microscopic examination. picture Tests used to identify bacteria include microscopic examination and immunoassay. The shape of fungal spores and the shape and location of disease lesions are useful in fungal identification. Viruses are difficult to identify correctly because the particles are so small and symptoms are so varied. An experienced person can make an educated guess as to what viruses may be present by assessing the plant symptoms, and then accurately diagnosis the disease using immunoassay tests specific to particular viruses such as Cymbidium Mosaic Virus. 3 - Just how potentially damaging is this ailment to the orchid collection? There is no cure for virus diseases. Infected plants must eventually be destroyed although with precautions, they can continue to grow and bloom away from the rest of the collection. Bacterial diseases can quickly destroy the first plant infected then spread rapidly to those nearby so they must be controlled aggressively. Some fungal ailments such as Black Rot are virulent, capable of infecting a range of genera and must be dealt with swiftly. Other fungal diseases are disfiguring but not immediately lethal. 4 - How does the disease spread? Poor growing conditions, too little light, inadequate air movement and high humidity, cold or warmth, are always a recipe for disaster for plants unsuited to those conditions. Bacterial and fungal diseases will spread rapidly, especially if the conditions are not corrected. Motile bacteria and the motile spores of Phytophthora can spread quickly in splash and water films on leaves. What you don't see is the tiny spore sitting on the leaf surface and finally sprouting an equally tiny hypha. By the time you see the fungal mat, the colony has been growing for several days. Of course, spore germination times will vary. Orchid plants infected with virus may or may not exhibit symptoms. All infected plants are reservoirs of infection but the disease can only spread by direct contact, by dripping onto another plant or in certain cases, by sucking insects. 5 - What measures are available to control
the disease? 6 - Is the best approach, 'toss' and try again? With badly diseased and, especially, virused plants, it is best to dispose of them. A thorough clean up of the growing area will be needed before obtaining new plants. Use bleach solution (1 part bleach + 9 parts water) to scrub all impermeable surfaces. Rinse metal surfaces afterwards with plain water to limit corrosion. 7 - What steps can be taken to ensure that
the same problem is unlikely to recur? Reduce the impact of diseases
in an orchid collection through sanitation and cultural practice.
b - Remove and burn diseased foliage and flowers. It is never wise to compost any diseased plant material. c - Use new or sterilized cutting tools. d - Treat cut surfaces with powdered charcoal, sulfur or a fungicidal powder. Even powdered cinnamon is anti-fungal but what we are doing here is drying the cut surface. e - Control pests. Sucking insects especially can transmit certain viruses or weaken plants. Watch for insects in new growth and inflorescences. f - Maintain good air movement within the growing area. Let plants dry off between waterings. Fungal spores require several hours exposure to continually moist conditions in order to germinate. g - Provide a light regime appropriate to the plant type. h - Do not crowd the plants. Crowded plants cannot easily be screened for problems neither can they be adequately ventilated. i - Cull plants that become easily reinfected despite good cultural practice. Some plants are more resistant to disease than others. Now we will look at some specific Orchid Diseases
Black Rot is a particularly aggressive infection of Cattleyas and other orchids caused by various species of the fungus Phytophthora. A new shoot suddenly turns black: the rot moves rapidly, killing the rest of the plant. A whitish 'bloom' of fungal tissue and spores may be seen on the diseased tissue. This disease is more prevalent during the rainy season in the tropics and is spread primarily by splashing water. It can also appear in damp, poorly ventilated crowded collections. Spores must be exposed to continuous moisture for more than a day for them to germinate and enter a plant part. Infection can also occur via cut surfaces. SYMPTOMS: New growth quickly turns black, usually from the base up. White 'bloom' of spores on surface. Smells somewhat fruity. CONSEQUENCES: Rot moves rapidly through rest of plant. Plant usually dies although aggressive removal of diseased parts together with adjacent healthy tissue can result in a cure. Highly contagious during rainy season in the tropics or in poorly ventilated, humid growing areas. John_in_Arcadia,_CA MarilyninOttawa
John_in_Arcadia,_CA MarilyninOttawa CONTROL: Disease spread primarily by splashing water. Stop watering/spraying and shelter plants from rain. Isolate infected plants. Burn diseased material. Wash hands after handling suspect material. Spray or dust with a locally approved fungicide. What did you do Jeanne? jeanne23_from_oz barbara_in_no._CA
Here we see a dry rot beginning at the base
of a leaf. It could be bacterial or fungal in origin but whatever
the cause, this leaf then others will be lost unless the disease
is controlled. Fusarium fungus grows within the conductive tissue of the plant, blocking the movement of water and nutrients. Often, even healthy appearing plant parts contain the fungus within. When cultured, the fungus which grows out produces telltale spores which assist in the diagnosis. picture Dendrobiums and Vandas growing in waterlogged potting materials are susceptible to a slow but inexorable rot of the roots and stem from below. The causative fungi are usually Fusarium and Rhizoctonia although other kinds may also be found. Here is a link to a fact sheet on Fusarium as it affects Dendrobium. button SYMPTOMS: Pseudobulbs becomes spongy and discoloured. The leaves, especially in Vanda, will yellow and drop off, one by one, until none are left and the plant dies. CONSEQUENCES: Plants can be salvaged if the infection is caught early. Uninfected pseudobulbs of Dendrobiums can be removed and these may form keikis. If a Vanda has many aerial roots above the diseased portion, sever the stem above the line of infection and pot in fresh medium. Success depends on the vigor of the plant, the length of the top cutting and the number of pairs of leaves. One can try to induce a root to form if the top portion has a dozen or so leaves. Place the cutting in a plastic bag together with a few strands of damp moss and hang it in a bright warm area out of direct sun. In order for keiki paste to work, you must expose a node where there is an 'eye' ready to form either a branch or a root. It could hasten the process. CONTROL: Since the disease is caused primarily by poor culture, fungicides are not recommended for control. In fact, it may be challenging to eliminate the disease from plants. Burn infected material. LEAF SPOTS and BLOTCHES (Fungi: Cercospora, Colletotrichum, Septoria, Phyllosticta) SYMPTOMS: Leaf-spotting fungi produce unsightly
speckles and blotches on the leaves of orchids such as Dendrobium,
Cattleya, Oncidium and Vanda. The spots are often rough to the
touch. There may be a halo surrounding new spots. picture
CONSEQUENCES: Premature leaf fall reduces plant vigor and flowering potential. Severely infected plants may die prematurely. Spots mar the appearance. It might be worthwhile to avoid spraying water for awhile, if you can. Improve air movement and remove any badly spotted leaves. Cattleyas can become infected but it is unusual under my conditions. Is your setup very damp, cool and is there no supplementary lighting to make up for the grey days of winter? CONTROL: Burn or otherwise dispose of diseased material. Improve air circulation and adjust temperature to plant type. Spray with a locally approved fungicide. BACTERIAL SPOT / ROT (Bacteria: Pseudomonas, Erwinia) picture Soft rots are often difficult to diagnose but whatever the causative agent, they can be devastating to an orchid collection. SYMPTOMS: Dark brown circular, fluid-filled blisters on leaves or in the crown of Phalaenopsis, Paphiopedilum, Catasetum. Fetid odor. Here is a link to a fact sheet on bacterial disease of Dendrobium. button CONSEQUENCES: Highly contagious. Crown rot
will quickly kill a plant. Because the bacteria produce enzymes
which dissolve plant tissue, an infection can quickly spread
within a plant and ultimately kill it. Orchids will be more vulnerable to infection if they are overfertilized, given insufficient light and ventilation, and if they are permitted to remain wet especially in the crown. Rots are a problem during the wet season, also after storms when plants are bruised and torn by high winds. CONTROL: Bacterial infections spread with water during rain, spraying and watering. Shelter susceptible plants from rain. Be vigilant for rot during the wet season. Withhold water from infected collections. Improve ventilation. Remove and burn infected tissue. Be careful
not to break the blisters. Consider the fertilizer being used:
reduce the nitrogen and increase the potassium component. Pot
Phalaenopsis so that the crown drains freely. Small isolated
leaf spots can be excised and the plant saved. Two viruses are transmitted solely by the grower. These common viruses are the Cymbidium Mosaic Virus (CMV) and the Odontoglossum Ringspot Virus (ORSV). They are most commonly spread with a cutting tool contaminated with infected sap. Other less commonly encountered viruses are spread by insects. Bean Yellow Mosaic Virus is spread from infected bean plants by aphids to Masdevallias and other genera. SYMPTOMS: Viruses cause odd patterns on leaves or petals, mosaics, diamond and ring shapes, stunted growth, stem distortion, and leaf roll. This plant tested positive for Cymbidium Mosaic Virus. picture This plant tested positive for several viruses. picture Here is a closeup view. button Tom in KY MarilyninOttawa This Dendrobium is said to have 'Curly Top', a virus-induced ailment. button Streaked blooms are said to show color break although this is not always a consequence of virus infection. button Sometimes there is no symptom but the plant fails to thrive. Other times, a beautiful, productive orchid is infected but the grower is completely unaware. CONSEQUENCES: Virus is one of the most dreaded diseases of orchids. There is no cure. Infected plants are reservoirs of infection. Virus can cripple, disfigure and weaken plants. Orchids may failure to thrive and there may be reduced flower production. CONTROL: There is no known cure! Destroy by burning, all confirmed infected plants. Isolate suspected plants. Always use sterile cutting tools when dividing or potting plants and when cutting flowers. art,simpsonville_sc MarilyninOttawa MarilyninOttawa For an excellent reference, refer to 'How to Control Orchid Viruses - The Complete Guidebook.' Gail C. Wisler. Maupin House Publishers, Gainsville FL art,simpsonville_sc Steve_in_the_Adirondacks MarilyninOttawa To obtain a saturated solution will of course vary with temperature but all you need to do is add more TSP until some crystals remain undissolved. Steve_in_the_Adirondacks MarilyninOttawa Jade_in_GR MarilyninOttawa |
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Prechat Handout Orchid Diseases: Part II - Problems and Solutions Marilyn H. S. Light You have just received the bad news. Your plant has an ailment, a pest or disease problem or both, and you have to decide what to do. This may be your one and only plant, a real favorite, or one that you recently purchased for a considerable sum. There may be many plants showing the same symptoms. You justifiably have that sinking feeling. STEP 1 - You have made a list of what you already know or have observed as symptoms and have overviewed any cultural aspects which may have caused the symptoms to appear. You may have consulted a club member or a disease diagnostic service. Be sure to have all the facts. Ask them the following questions.
1 - What is the specific name of the disease? Diseases have many common names. Ask about the scientific name of the organism.
2 - How certain is the diagnosis? A plant disease affecting commercial crops is never diagnosed on the basis of a single test but for some of the common ailments affecting hobbyist orchid collections, knowing the host plant, the symptoms, where it is being grown and under what conditions, and what the disease organism looks like (bacteria, spores, etc), can serve the purpose. A wide variety of tests are used to identify bacteria including microscopic and immunoassay. The shape of fungal spores and the shape and location of disease lesions are useful in fungal identification. Viruses are difficult to identify correctly because they are so small and symptoms are so varied. An experienced person can make an educated guess as to what viruses may be present by assessing the plant symptoms, and then accurately diagnosis the disease using immunoassay tests specific to particular viruses such as Cymbidium Mosaic Virus.
3 - Just how potentially damaging is this ailment to the orchid collection?
There is no cure for virus diseases. Infected plants must eventually be destroyed although with precautions, they can continue to grow and bloom away from the rest of the collection. Bacterial diseases can quickly destroy the first plant infected then spread rapidly to those nearby so they must be controlled aggressively. Some fungal ailments such as Black Rot are virulent, capable of infecting a range of genera and must be dealt with swiftly.
4 - How does the disease spread? Poor growing conditions, too little light, inadequate air movement and high humidity, cold or warmth, are always a recipe for disaster for plants unsuited to those conditions. Bacterial and fungal diseases will spread rapidly, especially if the conditions are not corrected. Orchid plants infected with virus may or may not exhibit symptoms. All infected plants are reservoirs of infection but the disease can only spread by direct contact, by dripping onto another plant or in certain cases, by sucking insects.
5 - What measures are available to control the disease? a - Isolate the infected plant(s). Do not spray or water especially
where the disease is waterborne. b - Using a sterile blade, remove diseased tissue plus a generous portion of healthy tissue and dust the cut edges with powdered charcoal or cinnamon. c - Control measures employing pesticides available to a hobbyist vary according to national, state and provincial regulations. Check locally. d - Virused plants should be either burned or disposed of in the garbage. Do not compost. 6 - Is the best approach, 'toss' and try again?
With badly diseased and, especially, virused plants, it is best to dispose of them. A thorough clean up of the growing area will be needed before obtaining new plants. 7 - What steps can be taken to ensure that the same problem is unlikely to recur? Reduce the impact of diseases in an orchid collection through
sanitation and cultural practice.
Orchid diseases BLACK ROT (Fungus: Phytophthora spp.) Black Rot is a particularly aggressive infection of Cattleyas and other orchids caused by various species of the fungus Phytophthora. A new shoot suddenly turns black: the rot moves rapidly, killing the rest of the plant. A whitish 'bloom' of fungal tissue and spores may be seen on the diseased tissue. This disease is more prevalent during the rainy season in the tropics and is spread primarily by splashing water. It can also appear in damp, poorly ventilated crowded collections. Spores must be exposed to continuous moisture for more than a day for them to germinate and enter a plant part. Infection can also occur via cut surfaces. SYMPTOMS: New growth quickly turns black, usually from the base up. White 'bloom' of spores on surface. Smells somewhat fruity. CONSEQUENCES: Rot moves rapidly through rest of plant. Plant usually dies although aggressive removal of diseased parts together with adjacent healthy tissue can result in a cure. Highly contagious during rainy season in the tropics or in poorly ventilated, humid growing areas. CONTROL: Disease spread primarily by splashing water. Stop watering/spraying and shelter plants from rain. Isolate infected plants. Burn diseased material. Wash hands after handling suspect material. Spray or dust with a locally approved fungicide.
BLACK LEG / DRY ROT (Fungi: Fusarium, Rhizoctonia) Dendrobiums and Vandas growing in waterlogged potting materials are susceptible to a slow but inexorable rot of the roots and stem from below. The causative fungi are usually Fusarium and Rhizoctonia although other kinds may also be found. SYMPTOMS: Pseudobulbs becomes spongy and discoloured. The leaves, especially in Vanda, will yellow and drop off, one by one, until none are left and the plant dies. CONSEQUENCES: Plants can be salvaged if the infection is caught early. Uninfected pseudobulbs of Dendrobiums can be removed and these may form keikis. If a Vanda has many aerial roots above the diseased portion, sever the stem above the line of infection and pot in fresh medium. CONTROL: Since the disease is caused primarily by poor culture, fungicides are not recommended for control. Burn infected material.
LEAF SPOTS and BLOTCHES (Fungi: Cercospora, Colletotrichum, Septoria, Phyllosticta) SYMPTOMS: Leaf-spotting fungi produce unsightly speckles and blotches on the leaves of orchids such as Dendrobium, Cattleya, Oncidium and Vanda. The spots are often rough to the touch. There may be a halo surrounding new spots. Microscopic examination will reveal the presence of fungus tissue and distinctive spores. CONSEQUENCES: Premature leaf fall reduces plant vigour and flowering potential. Severely infected plants may die prematurely. Spots mar the appearance. CONTROL: Burn or otherwise dispose of diseased material. Improve air circulation and adjust temperature to plant type. Spray with a locally approved fungicide.
BACTERIAL SPOT / ROT (Bacteria: Pseudomonas, Erwinia) SYMPTOMS: Dark brown circular, fluid-filled blisters on leaves or in the crown of Phalaenopsis, Paphiopedilum, Catasetum. Fetid odor. CONSEQUENCES: Highly contagious. Crown rot will quickly kill a plant. Because the bacteria produce enzymes which dissolve plant tissue, an infection can quickly spread within a plant and ultimately kill it. Orchids will be more vulnerable to infection if they are overfertilized, given insufficient light and ventilation, and if they are permitted to remain wet especially in the crown. Rots are a problem during the wet season, also after storms when plants are bruised and torn by high winds. CONTROL: Bacterial infections spread with water during rain,
spraying and watering. Shelter susceptible plants from rain.
Be vigilant for rot during the wet season. Withhold water from
infected collections. Improve ventilation. Remove and burn infected
tissue. Be careful not to break the blisters. Consider the fertilizer
being used: reduce the nitrogen and increase the
VIRUS DISEASE (all orchids) Viruses are extremely small organisms composed of either RNA or DNA and often surrounded by a protein coat. Viruses replicate only inside living cells. Viruses overtake cell metabolism, causing it to manufacture more virus particles. Viruses enter plants in various but specific ways including transfer of cell sap during feeding by aphids, mechanically from contaminated plant sap on hands, tools, or in dripping water from pots above, and during vegetative propagation including mericloning and division. Two viruses are transmitted solely by the grower. These common viruses are the Cymbidium Mosaic Virus (CMV) and the Odontoglossum Ringspot Virus (ORSV). They are most commonly spread with a cutting tool contaminated with infected sap. Other less commonly encountered viruses are spread by insects. Bean Yellow Mosaic Virus is spread from infected bean plants by aphids to Masdevallias and other genera. SYMPTOMS: Viruses cause odd patterns on leaves or petals, mosaics, diamond and ring shapes, stunted growth, stem distortion, and leaf roll. Streaked blooms are said to show color break although this is not always a consequence of virus infection. Sometimes there is no symptom but the plant fails to thrive. Other times, a beautiful, productive orchid is infected but the grower is completely unaware. CONSEQUENCES: Virus is one of the most dreaded diseases of orchids. There is no cure. Infected plants are reservoirs of infection. Virus can cripple, disfigure and weaken plants. Orchids may failure to thrive and there may be reduced flower production. CONTROL: There is no known cure! Destroy by burning, all confirmed infected plants. Isolate suspected plants. Always use sterile cutting tools when dividing or potting plants and when cutting flowers.
Steps to keep virus infection out of a collection. a - Assemble a collection of virus-free plants. Seedlings in flask are less likely to be infected than divisions of plants long in cultivation. b - Use sterile cutting and potting tools. Sterilize cutting tools after each use by soaking for 10 minutes in a solution of either 10% liquid bleach or saturated trisodium phosphate solution. c - Test plants for the presence of virus. d - Destroy by burning or at least isolate proven infected plants.
Saturated tri-sodium phosphate (TSP) Add 1/2 cup of TSP to 2 gallons of hot water. CAUTION The solution is very corrosive. Mix well using a wooden paddle. Add more TSP until some crystals remain undissolved. A saturated solution is necessary to inactivate virus.
Resources Crop Knowledge Master Database http://www.extento.hawaii.edu/kbase/crop/crops/cattleya.htm Common Virus Diseases of Orchids http://web.aces.uiuc.edu/vista/pdf_pubs/614.pdf Orchid Diseases in the Northern Territory (Australia). J. Duff and A. Daly, 2002. AgNote 568, No. 13. http://www.nt.gov.au/dbird/dpif/pubcat/agnotes/pests_diseases_plants/568.pdf Pests & Diseases Section of the Philippine Orchid Society |
