Question
I have had several staghorn ferns for years and am experiencing a problem with all of them (6 in total) that I have never had before.
The ferns are turning dark brown like burnt and it is happening to all of them even some browning in the caps attached to the trees.
thinking it might be some kind of fungus, I sprayed them last night with a copper solution but don't know if this would be the solution.

Answer
Armando hi;

I would be happy to help but would probably need more information.  A photo would be best.

The "shield", which is what you call the cap (attached to the tree), is expected to turn papery brown over time.  That is normal, but I am surprised it is only happening now.

If, however, it is a dark, mushy, smelly brown, then you may have a fungal or bacterial problem, often associated with high rainfall.

If the tips are brown (with powder underneath), then your fern has become fertile and is ready to reproduce.  This is not a problem but may indicate some stress (heat? drought?).

An occasional copper spray can be a good preventative measure, but cannot really cure a sick plant.

In order to better qualify my answer, I would need a detailed description (and photos, if possible, near and far) of what you are seeing, and what have the plants experienced the past few months.  

DC