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

Stanhopea Spring Culture Checklist

 

Winter Wrap Up

The winter of 2013 was particularly difficult for growing Stanhopea.  In January the temperature dipped to 31°F (-0.6°C) for only the second time since I have lived in San Diego.  This low temperature duration was only for a few hours on one night, but it was unusual in that is was part of a 10 night period in which temperatures ranged from 35-39°F (1.7-3.9°C).  This long cold period was particularly difficult for several of the Stanhopea. Some orchids exhibited  bacterial growth presenting a few days after the cold snap along with a loss of  few leaves after several weeks.  In addition to this cold, a very intense hail storm occurred one night and caught me off guard.  Most of my Stanhopea collection is sheltered by trees, roof overhangs, and plastic saran; however, a few plants were partially unprotected during this storm and took some damage.  If I continue to have these tough winters, it will give me incentive to complete the building of a cool greenhouse to protect the orchid collection better by next year.


Stanhopea shuttleworthii growing underneath a tree canopy.  The plant looks good from a distance (left).  However the hail storm damaged the right side of the leaf causing pitting and the cold weather cause bacterial spotting (right)

Stanhopea Spring Culture Checklist

·         Begin watering these species regularly when new growth begins (S. hernandezii, S. insignis, S. jenischiana, S. lietzei, S. maculosa, and S.martiana).

·         Begin fertilizing all species regularly once new growth begins.  I often reduce the manufacturer’s recommendations in half and fertilize every week or what is known as weakly-weekly.  Stanhopea can be rather heavy feeders when they are in active growth.

·         Weed baskets to prevent ferns and other plants from taking up space in baskets.

·         If you grow Stanhopea in a sunny area or a greenhouse that receives strong sunlight you may want to place saran shade cloth over the growing area in early spring before the sunlight becomes too strong for them.  You may also want to consider moving the Stanhopea to another shadier growing area.

·         Use of methaldihide products is advised on a weekly basis at this time to prevent slugs from disfiguring new growth and impacting new inflorescence and bud growth.  I often use a product called “That’s It” that is a granular form and therefore leaves less residue in the growing media.  I am currently testing some more organic methods of slug control.

·         In mid to late spring make sure to check for growing inflorescences and ensure that their growth is unimpeded by other plants or the basket.  If need be place a plastic label underneath the inflorescence to help direct the growth out of the basket.

·         Spring is the second best time to re-pot or re-basket Stanhopea, I think late fall is actually the best time because most Stanhopea have already bloomed and are in a rest period.  It is recommended that you allow new growth to begin before you re-basket so that the growth can mature somewhat before you transplant the orchid.  This will prevent the new growth from being impacted during the process.  Early spring is a good time to transplant because it will also prevent damage to most nascent inflorescences.

·         Keep a careful eye out for spider mites as the spring continues and our weather begins to warm and dry out.  Small yellow spots on the foliage signal that these pests are active on your Stanhopea.  Spray infected areas with an insecticidal soap to kill the pests as soon as possible to prevent them from damaging the plant further and spreading to other orchids.

·         You should also be diligent in keeping watch for fungus infections at this time on leaves.  Several fungus attack leaves when humidity is high and temperatures are warm. Black or brown spots of leaves and yellowing of leaves in odd patterns are usually the cause of fungus or bacterial infection.  Treat with a fungicide or bactericide.  I often use Physan 20 to deal with the problems and prevent further damage to the plants.