Yellow Spotting/Pitting on C. intermedia Seedling - Orchid Board

galguibra · #1 07-31-2024, 02:36 PM

I've had this cork-mounted C. intermedia seedling for a few months now, and it's seemed to be doing well up until now. The roots have been growing really vigorously the past few weeks especially, but I'm now seeing some translucent yellow pitting/mottled discoloration on both of the only two proper pseudobulbs and I'm not sure what's causing it.

For reference, this is a picture from ten days ago:

The lighting is a little different there than in the pictures from today, but still there's only some subtle mottling. I hadn't really thought too much of it at the time since the plant was growing well, but yesterday I noticed it had started to go translucent, and that the leaves were pitting too. Today it looked even worse, so I'm starting to get pretty worried at this point

That I'm aware of, the seedling's only pest/disease history is that when I first got it in the mail a little over two months ago, I found a millipede in the pot. I didn't notice any obvious damage then, though, and it's been doing well until just recently, so I feel like something else must be going on. I did have a fly/fungus gnat problem in my apartment a little while back, but I use mosquito dunks in my water as a preventive measure and I haven't noticed anything on the mount or any of the roots or anything, and the issue has since been resolved.

The only recent cultural changes I can think of were that a little over three weeks ago I started soaking the mount in a bucket in addition to misting since it dries out so fast, which it had been seeming to like and responded well to, and then I also recently switched over to K-Lite and have been feeding a much more dilute solution than I used to. I did have to skip watering it for a day since I wasn't home, which I know isn't ideal, but I soaked it well before leaving and then made sure to water it again as soon as I got back. I feel like that shouldn't cause this kind of damage anyway, but I didn't wanna leave anything out just in case.

I have the plant under full-spectrum LEDs at around ~400 PPFD, but it's been that way for a while and it never seemed to mind. There's pretty good air circulation in the room with fans running 24/7 (never blowing directly on the plants), and the humidity by the plants is nice and high at around ~65%. I keep the temperature at around ~75°F during the day and ~65°F at night, but it's also drier at night to compensate.

I only water with distilled water, and the fertilizer has always been well-diluted. Before I started using the K-Lite, I had been DIYing something with about the same nutrient ratios across the board as the ~13-3-15 MSU mix, but using synganic component nutrients that are all chelated with organic acids and have worked well on my other plants.

I can't think of any specific reason why the leaves would suddenly start showing this kind of damage, so I'm worried it might be some kind of fungal/bacterial/viral attack. Hoping somebody on here can help diagnose/treat the issue, since this plant has a lot of sentimental value

estación seca · #2 07-31-2024, 08:15 PM

I think it's partly related to too much light, leading to too much heat.

Not all photons are used for photosynthesis, nor reflected. Some generate heat in the leaf. Small seedlings have a greater surface area to volume, so they heat more than larger plants under the same light. If conditions are breezy the heat will be carried away. Seedlings in general are safer with dark green leaves, and light lower than would be tolerated by adult plants.

I have also seen something like this in Catts., Phals. and Vandas, when cool water hits warm leaves.

Has the temperature inside risen recently? That would lead to decreased cooling of the leaves, and also an increased temperature difference between leaves and the misting system. There is no harm in having a breeze blow on the leaves, other than needing to water more often.

I would try and move the plant further from the light, until the leaves are a deep green, and not yellowish green.

galguibra · #3 07-31-2024, 08:31 PM

Quote:

Originally Posted by estación seca

I think it's partly related to too much light, leading to too much heat.

Not all photons are used for photosynthesis, nor reflected. Some generate heat in the leaf. Small seedlings have a greater surface area to volume, so they heat more than larger plants under the same light. If conditions are breezy the heat will be carried away. Seedlings in general are safer with dark green leaves, and light lower than would be tolerated by adult plants.

I have also seen something like this in Catts., Phals. and Vandas, when cool water hits warm leaves.

Has the temperature inside risen recently? That would lead to decreased cooling of the leaves, and also an increased temperature difference between leaves and the misting system. There is no harm in having a breeze blow on the leaves, other than needing to water more often.

I would try and move the plant further from the light, until the leaves are a deep green, and not yellowish green.

Okay, that's at least a lot less stressful of a problem to have if that's the case !! I brought the light down to about 75% of what it was before, and adjusted the fan to move some more air in that part of my room. I don't think the air temperature inside has really been any different recently, but I have been trying to get the humidity down, since I was getting some peaks of ~75-80% before (basement units smh) and that's just not sustainable. The humidity is down closer to 65% these days, so maybe that lowered the plant's effective heat tolerance.

And now that I'm thinking about it a bit more, I did also start using warmer water for the daily soaks in the past few weeks than I had been when I was just spraying with water. The water temperature probably went from ~70°F to like ~85°F since I recently got a C. aclandiae seedling and wanted to help keep it warm without heating up the rest of my place. I don't ever cross contaminate the water/vessels between plants, but I definitely wasn't going to mix up different temperature fertilizer soaks haha. Maybe that contributed too, and then the combination of everything ended up being too much. Should I just stick to room temperature water to make sure the misting water isn't a temperature shock later?

estación seca · #4 08-01-2024, 03:42 AM

I think lowering the light will be adequate.