We planted several salal (Gaultheria shallon) shrubs next to our driveway about five years ago. Over the past couple of years, we've noticed brown spots appearing on the leaves. The shrubs still produce blossoms, but not much fruit for the birds. I'm concerned that the shrubs have developed a heavy Phyllosticta infection, which seems to involve almost every single leaf. Is there anything we can do, other than ripping out these shrubs and starting over?