I few years ago I planted a group of 8 azaleas in my yard.

Five of the azaleas are growing and healthy and bloom well each spring but 3 of the plants are runty and have a growth that I thought was a fungus. It appears that it is a folicose form lichen that grows gray leafy stuff along the limbs. On these plants, the leafs are sparse and small and the blooms are small in the spring. It may be that these 3 are a different type but should they be sprayed with a fungicide or fertilized diferently? The healthy plants do not have any visible lichens. Thanks.