I recently bought another phal and when I got home I noticed that there are some black/yellow marks on the leaves. I have the plant for couple weeks and the yellow marks seem to fade away but the black ones are still there. Any advices?
Thanks in advance!
I'm not an expert, but I would suspect an older sunburn followed by a fungal/bacterial infection on/around the dead cells.
I would address this in two steps:
1) Dust the black area with ground cinnamon, which is a great natural antifungal.
2) If the black area seems to spread, cut it. Make sure you cut well into the healthy area (1 cm at least), sterilize the tool before and after, and dust the cut with cinnamon.
My 2 cents.
The 2nd pic acutally looks like an old wound where the stake was jabbed through the bottom leaf. If that is the case is has healed and is merely unsightly. Cant see anything wrong in #3. However, #1 pic may be something. I would cut it at least 1/2 way down the leaf, and if the plant otherwise looks healthy and growing---cut the whole 'infected' leaf off. Do watch for spreading if you decide to wait. Sometimes plants just stress from moving from purchase to home.