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My Articles About Orchids
Pythium infection
   Smoggy inversions during the winter are common where I live and the terrible air quality can really cause havoc on my beautiful blooms. The sepals curl and turn brown and the flowers just give up and die prematurely. During the winter I learn to expect this.

   However, I knew something other than bad air was wrong with my prized Cattleya 'Sapphire' (this Cattleya is one of the famous "blues" that was produced using Cattleya 'Ariel Coerulea' in 1969)
   I pulled the outer layer back from the double sheath it had produced. Opening double sheaths is a normal procedure to assist the blossoms to develop properly.

   I was surprised when water spilled out after I opened the outer sheath. This is not normal and something you do not want to see. I cut the top of the inside sheath and discovered that it too was full of moisture. I left it open to dry in hopes that the buds would not rot and everything was ok. After the surgery, the buds continued to grow, so I thought the problem was solved and everything was just fine.
   When the Cattleya bloomed I was struck with the reality that I had not prevented the damage to the buds after all. The flowers never opened fully and only lasted a few days before completely falling off.
   The flower sheath had turned brown and mushy in a very short period of time. Upon further investigation, I became convinced that it was a water mold fungus that had attacked the developing buds.

   I suspect the fungus Pythium ultimum was the guilty party.
  This fungus exists only in environments where there is free water. It has mobile zoospores, which swim in water and on reaching the plant surface these mobile spores penetrate into the plant. In the next stage of its life cycle the fungus develops a mycelium consisting of thin, thread-like hyphae, which spreads fast in the affected plant tissues. The first visible signs of the infection are small, watery, translucent spots soon expanding and changing to brown. Affected parts can become dry or mushy as the whole plant starts to have a devitalized appearance.

   I knew I had to hurry if I wanted to save my Cattleya 'Sapphire'. I knew this disease was infectious and would spread quickly to other plants in the moist, crowded environment of my winter greenhouse if I did not do something about it. It is important to know that while high temperature in general favors fungal infections, alas, Pythium ultimum can be active even at rather low temperatures, including in cool greenhouses. The flowers wilted due to the infection to the flower stem that feeds the flowers.

   I quickly put my Cattleya 'Sapphire' in quarantine away from all my other orchids. I then preceded to take the necessary steps to try and save my precious orchid.
   I removed about 1/2" of diseased tissue. I then dusted the exposed cut surface with the fine charcoal to prevent infection. There is no need to buy expensive medicines. Simply grind a plain barbecue charcoal briquette into a fine powder or you can even use some ground cinnamon to treat wounds. I then replaced my orchid on the quarantine rack.
   I stopped regular watering giving my orchid only enough water as necessary to keep it alive over the next few weeks. You want to keep the moisture limited around the plant to prevent giving the fungus what it needs to survive but not so dry as to kill your plant.
   Always try to save the pseudobulbs even if you have to cut it back. At the base there are quiescent buds from which new growth will emerge. In some cases cutting back the top of the bulb will activate the buds and promptly resulting in new growth.
   In the meantime one of my Dendrobiums, 'Burana Jade' became infected with the same disease. This was caused from water dripping into the center of the plant, from condensation on the roof of my greenhouse. I preformed the same procedure on the Dendrobium as I had on the Cattleya.

   The damage was much greater since it was in the main crown of the pseudobulb. I treated the Dendrobium by cutting away all the growth that was infected and treating the infected area with ground charcoal in hopes that I would be able to save this pseudobulb and stop the disease from spreading to the other pseudobulbs that were growing in the pot.
   After working with infected plants you need to take steps not to contaminate your healthy plants.

   Be sure to wash your hands, sterilize all equipment used around the infected plants, and to remove any infected cuttings from the greenhouse. Remember this disease is contagious and can spread!

   After discovering this infection I also started to spray my greenhouse and all the other plants with a disinfectant. I personally use RD-20 fungicide and I really like it but there are many other brands, which can be equally suitable.
   I also added another fan to keep the air moving which helps the stagnant cool air and dries the leaves of the plants; the extra fan has also helped reduce the condensation that forms in my winter greenhouse.
   Three weeks later I was happy to see I was able to save my beautiful Cattleya. The cut had dried and I knew the infection had been stopped. Unfortunately I lost the pseudobulb on the Dendrobium. The pseudobulb continued to decay and finally dried up.
   I was successful stopping the disease from spreading to the other growths so the plant will be OK. At the first sign of problems you must react or in a very short time you could lose your orchid entire collection!