PLEASE HELP! I'm going crazy trying to fix this problem with phal bellina and gigante
 

Hi again. So I posted a bit ago about a gigantic alba and asking what the problem is and someone said maybe cold damage. But it spread a bit and I don't think cold damage spreads? So I cut off the affected part of that leaf and so far so good with that. The thing is, something similar happened to my phalanopsis bellina in June. I cut off the affected part and she's been fine since. However, today I looked and she's having the same issue again. But I don't get why because overall they seemed healthy. Although currently the bellina specifically looks a little rough. I have a timeline of my photos with labels. Please help me figure this out. It'll break my heart if I lose these 2. They're my favorite. the white stuff is diatomaceous earth for pests and use mosquito dunks for some gnats. And the issue is always at the tip of the orchid leaf.

Without know exactly how your caring for the plants, there is no good way to speculate on what's happening.

The first thing I'd do is get rid of that DE. It has no effect on gnats.

I've looked for bugs and I haven't seen any. I put diatomaceous earth on my plants. Shouldn't that prevent most pests?

---------- Post added at 06:55 PM ---------- Previous post was at 06:52 PM ----------

I have the de for pests in general and I do water them with mosquitoe bits in the water. They are on a window sill in the bathroom, I water when they are dry, the window has a frosted covering so it is filtered light. And I fertilize with repot me fertilizer drops and I water with tap water. And I live in Florida so it's decently humid. All my other orchids seem totally fine. I have typical household phalanopsis, a cattleya, a mini mark, and 2 oncidiums and none of those have any issuess

How cold has it been outside? If they were close to a cold window that could be cold damage.

Their leaves were touching the glass. It got into them 50s maybe the 40s?

That is the problem. Those are cold damage. Phal. bellina frequently dies if it gets below 70 F / 21C.

I agree. Both bellina and gigantea will never see temperatures below the 70’s in nature, with bellina craving even higher.

But why would it have happened to the bellina in June?

Cold can be damaging by itself, and the weakened tissues can become susceptible to diseases.

Are they grown in A/C during the summer?

They are but they are by the window which makes it warmer in that spot. And it did great after I got rid of that one spot in June. She even flowered for me. I'll get her a terrarium and a temp humidity gage and be better about keeping her warm. I approve your help. It means a lot.

If sun struck that window in June it might have raised the temperature of the glass to a dangerous level. It only takes a few minutes for that to happen. Localized heat and cold damage look almost the same on most plant leaves. It is often caused by being too close to a window, getting sun during the change of seasons, and being too close to electric lighting. We regularly see people posting photos like this here on Orchid Board.