Wednesday, July 10, 2013

Stanhopea Diseases


 
Stanhopea are relatively easy to grow and have few problems when cultured properly.  The most bothersome problem I have found is brown spot and anthracnose in some species and hybrids.  I have provided the following partial list of diseases that I have found susceptible by Stanhopea.  However, there are other diseases and viruses that can affect Stanhopea similar to other orchid genera.  I have included a link at the end of the text for further assistance.

Bacteria:

Acidovorax (Pseudomonas) –This starts as a blister that is small, green/brown and eventually enlarges to a brown or black dried and sunken spot.   Bacterial Brown Spot is a water –borne pathogen that thrives in warm and moist conditions.  Increase air circulation and reduce overhead watering.  Spray the plant with a bactericide (e.g., Physan and copper solutions).

Fungus:
Anthracnose (Colletotrichum and Glomeralla ) This fungus affects the leaves and turns the apex brown and then moves to the leaf base.  This often occurs as bands across the leaf, and for me occur often in the early spring with the weather warms and it is still moist.  This is a fungus that is common when air movement is low, temperatures and humidity is high, and light levels are low.  Use a fungicide such as Cleary’s 3336 to prevent further infections.
Black Rot (Phytophthora cactorum and Pythium ultimum) This is a fungus that is present in some orchids and often attacks new leaves and growth.  This infects the vegetation and causes translucent spots and then the tissue dies (necrosis)and turns black in color.  I have not had a problem with black rot on Stanhopea, but rather other orchids in my collection have been susceptible to this fungus.  Removal of the infected plant parts should be accomplished and standing water should be removed in the growing area to reduce infection.  A fungicide such as Cleary’s 336 can be used to prevent further infections.
Botryis is a fungus that often produces brown spots on orchid flowers which are dead cells (necrosis).  The fungus overwinters on dead and rotting vegetation.  Make sure to keep the growing area clear of dead vegetation and lower humidity below 90 percent.  This is not a serious threat to the orchid plant but disfigures the flowers.
Cercospora Leaf Spot (Cercospora spp.) This often begins as a yellow spot under the leaf and then is noticeable on the upper surface.  This infection spreads through the leaf and the spots are sunken and turn black or brown.  Infected leaves fall prematurely. This is a fungus that is common when air movement is low, humidity and moisture on leaves is high.  Use a fungicide such as Cleary’s 3336 to prevent further infections.

Viruses:
Stanhopea ringspot is a virus that causes yellow spots and rings that are circular or diamond shaped on a green leaf background.   The symptoms occur on older leaves or mature leaves.  This virus has been noted on some Stanhopea, though it  is not common.  I have not had much experience with viruses in my collection and tend to keep my growing area clean and ensure that all my tools are disinfected before each use on a different plant.  If you notice that there are signs of virus on your plant, isolate it from the rest of your collections and seek advice from a competent orchid grower.

For further reading see the AOS Orchid Ailments

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