Hi,
I bought a small staghorn fern without examining it carefully. Afterwards I noticed a dark blackish spot near the eye of the top green sterile frond and there is also a dark area on the frond underneath. The plant seems healthy other than the dark patches. Is this a case of the start of the natural browning process of the sterile fronds or is this potentially disease (rhizoctonia?). I gave it a thorough watering when I bought it last week and am currently letting it dry out.

I'm not familiar with what Rhizoctonia infection looks like on Staghorn Ferns but just in case that black spot is the beginning of a fungus of some sort, I'd stop watering for awhile. Too much water along with high humidity and lack of air circulation can cause fungal infections to spread. You might also want to sprinkle the black spot area with a little ground cinnamon, which is a natural fungicide.

Thanks as usual plantladylin. I really hope it's not a fungal infection or worse. I've applied cinnamon to it but hope it's just the natural ageing of the frond. It does look a bit suspect though esp at that location. My plant smells lovely now at least.

I keep a small container of cinnamon in my garden supply bucket and I love the fragrance so much that I sometimes wish I could find a spot on a plant ... just to have a reason to sprinkle it on a leaf.