thanks Benno, that actually makes a lot of sense.
the fact that the "rot" moves down the leaf, and come back despite me cutting into healthy tissue.
and the fact it moves rather slow (maybe one centimeter per month).
i'll finish reading these papers, and see how i can improve.
all my plants are sitting on a south facing windowsill (Israel), in my living room, which had air-conditioning during summer, especially on weekends.
at the beginning of summer this window was exposed to direct sunlight only in the late afternoon, so i kept the blinds open all day long, putting Catts and Den.Phals in front, and Oncidiums and Phals on the back.
in mid summer the window started to get exposed to full sunlight earlier in the day, and i had some sunburns (leaf temperatures of about 40c), so i closed the blinds half way (to slits mode).
i'm usually using rain water i collect in winter, and water from air conditioner in summer. these have about 20ppm of dissolved solids, and i'm fertilizing weekly weakly, with some generic orchid fertilizer (which i'm not sure what it contains).
i use 1/4 strength, which gives me about 200ppm.
I was soaking the the pot in water for about 20 minutes, once a week in summer, and i'll probably go to once in two weeks in winter.
during the hot summer months, the media (mostly medium bark, with some sphagnum dressing at the top), appeared to be drying up rather quickly, so in between the weekly watering, i used to spray some A/C water on the top dressing in between watering (about 2 to 3 times per week).
near the end of summer, i started using the bamboo stick method, and i did notice the stick seems to be slightly wet, and cold, even though the media appears dry.. so i might have been watering the Catts too much.
here's a photo from afternoon in early summer.
contagious rot in Cattleya new growth
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