This problem is most common in areas of low rainfall. It also occurs in soils with poor drainage, and where too much fertilizer has been applied. Excess salts dissolved in the soil water accumulate in the leaf edges, where they kill the tissue. These salts also interfere with water uptake by the plant. This problem is rare in areas of high rainfall, where the soluble salts are leached from most soils. Poorly drained soils do not leach well; much of the applied water runs off the surface instead of washing through the soil. Fertilizers, which are soluble salts, also cause salt burn if too much is applied or if they are not diluted with a thorough watering after application.
Salt burn damage does not disappear from the leaves, but injury can be avoided in the future. In areas of low rainfall, leach accumulated salts from the soil with an occasional heavy irrigation (about once a month). If possible, improve the drainage around the plants by removing them and adding soil amendments. (For instructions on improving drainage, see Soil Types, Soil Structure, Groundwater.) If plants are severely damaged, replace them with healthy plants. Follow package directions when using commercial fertilizers; water thoroughly after application. Avoid the use of bagged steer manure, which may contain large amounts of salt, on azaleas and rhododendrons.
Plant Care for Rhododendron