treating / preventing bulb rot
 

I lost several orchids (maybe 15?) recently - about half of my collection. In almost all cases, they ended up getting some sort of rot (in the roots and or pseudobulbs), which kept coming back despite aggressively cutting away diseased parts and sprayed with diluted Physan. After I treated them, I experimented with spag-n-bagging, putting some of them in moss, some in bark, and some in S/H, but have yet to save one of them.

So I have two questions:
1. What conditions could be causing this? My guess was inadequate air flow and/or too high moisture with no drying out, but maybe I have some sort of pathogen?
2. Is there any effective way to treat rot once it happens? I have a few plants clinging to life at this point, but what I'm more worried about are the plants that I still have - could be the difference between an expensive lesson and just quitting the hobby altogether.

- Tom

Tom, we've dicussed this before on the board, but rot is caused by a couple situations: lack of oxygen at the roots (root rot) mostly due to excess moisture which fills the air cavities with water. And on the leaves, by standing water which enables bacteria to breed, leading to rot (introduction of mold and other bacteria). What you can best do to prevent it is to be more diligent with watering. This means mostly letting the roots dry down before the next watering. How do you do this? The best way I know of for casual growers or beginners is to use clear plastic pots. This way, you can see if the medium is still wet before watering again. I still tend to use these pots and I have been growing for more than 30 years. As for leaves... quit spraying down the plant in an attempt to humidify it. It doesn't humidify and does spread fungus and rot. It's better to grow in a very dry environment than to try to wet down the plants' leaves. Spraying the roots or surface of the mixture is OK (I do this myself once each day) but don't spend a lot of time spraying the leaves.

Now, once you have the rot, what do you do? I choose to use Thiomyl which is systemic and a potent rot curative. However, to work, you need functioning roots. Once the roots are totally mush, then this won't work as well. It does, however, sort of work systemic on leaf rot. This is totally dependant on the species of orchid. I have had great success with some of the Angraecoides which have larger stomata and less success with Cats and Potenara, etc which have smaller and less stomata.

Don't quit the hobby! Just learn from it. It can get expensive, but learning is worth the effort, as far as I am concerned. Hope this answers your questions.