Hi

It has a fungal problem , all this wet weather doesn't help that's how it spreads from spores, the rain splashes them about.

Have you in a pot or in the open border/soil ?

Normally lower leaves are infected the worse and the fresh new growth should be fine , if possible pull don't cut the lower leaves off and burn them also pick up any old leaves on the floor and throw out don't compost them.

A fresh layer of mulch around the bottom of the plant also a weekly feed will help.
Its something they get now and again but hygiene is the best remedy.

I have never tried a fungicide spray , see what other on here may come up with .