this might be a fungal disease and from what i have read of it, it looks like cleaning up the base of the plant from debris might help, it doesn't look like you have much congestion of leaves... btw looks like a nice healthy plant otherwise... mine is suffering in every which way :(

The yellow stippling makes me think mites. Check the undersides of the leaves carefully, you may want to use a hand lens. Mites feed by sucking out the inside of the leaf, leaving an empty void. Each feeding void appears as a yellowish spot, and many voids will appear yellow to white. The leaf will tend to become dry, and due to the loss of moisture then becoming brown around the margins, and eventually fall off.
IF you see mites, which are typically very small, with 2 spots on their bodies, then you will have to treat for them.