I have a mass planting of dwarf Mexican Petunias under a sago palm . They have been there for 6 years and always have a great display of flowers. Something has attacked them and they are losing all their leaves and are dying off. We were gone for a couple of weeks and came home to see them in rapid decline. The leaves are mottled with a brown fungus?and curling up, yellowing and dieing.I hav no idea what it is or what to treat with. Any help? Pic is attached showing infected leaves. Thanks