a pressure washer will not remove the stain since most stains are not superficial, but penetrate into the wood. Of course if you have a sealer, then that might be removed.
If you get a 2400 psi with a fan spray tip, this should not damage your deck finish IF you don't get the wand too close.
If this is NOT an option, try some cleaner on those isloated spots.
I always suggest that every deck owner every spring rent a washer and clean the deck the throats, and the wood itself. This is a good "preventative maintenance" procedure.
Now, find out what is causing the stain in the first place, is water standing, is debris holding on the deck in that area, is there a plant that you are feeding and the drainage water is leaching onto the deck, this water could have iron, fertilizer, and other chemicals causing the problem.