If you have the fungicide and you have the time to spray it now it sure won't hurt anything to spray the new growth. How much it will help is questionable at this stage. It may make little difference or depending on the overall health of the plant it may slow things down a bit. I'd take the time first to remove all the affected foliage from the garden first though. That can help as much as the spraying.

At this point it is basically a 50/50 game plan at best so it's your choice.

Dave

Thanks Dave. If nothing else, I'll remove the dead foliage.

Yes - You should spray or it might spread and kill the whole plant. I have had early fungus problems and now I have spider mites and Late Blight. If you get Late Blight, it will kill the plants very quickly. Spay a copper based fungicide once a week or after every rainfall.