Dendro with spots

[SaraJean]

I’ll give this a shot. What type of Dendrobium is this and how long have you had it?
I’ve had this exact thing happen on a few of my Latouria and Spatulata type Dens. Occasionally an older leaf, here and there, will look like this before it falls off but that is more age related. If you have had many leaves fall off on most or all of your growth that’s an issue. When I had this happen on mine, it was usually caused by one of two things
1. Damage to the leaf that introduced a small localized infection. I.e mechanical damage or sunburn, leaf got cold and wet... resolved itself, didn’t spread to other leaves, didn’t bother treating because the leaf falls off anyways.
2. Wasn’t getting enough water. That resulted in them dropping leaves like hot cakes
Because- A: wasn’t watering orchid enough, or, B: orchid had a poor root system and the couldn’t take up water.

I would check your roots, honestly. And the physan is probably doing more harm than good depending on how you are using it (personally, I use it to disinfect my tools, inorganic media, and surfaces only; not actually on my orchids).

For the oncodium, could you post pics? Im not nearly as comfortable with those as I am with Dens but pics always help. I like to use Thiomyl (Clearys) for a fungicide if necessary. But I rarely tend to treat my orchids and I never treat something unless I know for sure what I’m spraying for (like bacteria vs fungus, scale vs thrips vs sunburn, snails vs root rot) . The best advice I have ever been given was from someone who has been growing orchids for over 40 years: Find out what’s causing issues and fix that. That little nugget of wisdom made me want to smack my head and say “DUH!”. It completely changed how I looked at growing my orchids for the better with being proactive rather than reactive. Btw, How’s the air movement around this one?