there is a tropical plant forum ... if not a palm forum... you might find other experts to opine on this plant ..

but that wont stop me.. lol ... when is the last time you cut off the old old branches .... its supposed to be done yearly or so ...

if you havent ... and this is one of the bottom most .. oldest fronds.. if that is the right word ... then it really doesnt matter what you are seeing.. or thinking about treating for such ... ask yourself.. why is your first thought.. WHAT TO USE????

because MAYBE what you are seeing is old age ...

i cant really tell.. from your pic ... and i am presuming.. that it was not recently planted ... you gave us more facts on the maple.. than you did on this plant ...

i wish you luck ...

ken

That does not look like normal aging of a palm leaf to me. I believe your palm is a Butia (probably capitata), otherwise known as a Pindo or Jello Palm. It might be a fungal disease of some sort. In general these kinds of issues are more or a problem with excessive humidity. Have you had excessively humid or wet weather? Have you been watering frequently? To reduce the chances of a palm getting this, try avoid wetting the leaves if watering. The palm does not appear to be crowded by other plants (ventilation is useful). Also, I would remove the most affected leaves as this might aid the spread. Good news is that a palm can completely grow out of this. The leaves that are already affected will not revert to normal, but new growth will be fine once conditions improve.(I once had a Canary Island palm delivered to me from Miami that came covered in black spots, figured it was related to South Fl.'s Summer humidly, as Phoenix prefer a drier climate....I kept the plant and soon the new leaves grew in fine.)

Here is a link that might be useful: Possible diagnosis