In moist, humid climates, azalea shrubs fill the yard with blossoms from spring to autumn. Azaleas, which are available in both evergreen and deciduous varieties, are susceptible to several foliage problems. Commonly, these foliage diseases contribute to leaves turning brown and premature leaf drop. Proper watering and fertilisation are key to growing healthy azalea shrubs.
Inappropriate fertilising causes azalea leaves to become dried out, crusty and brown. These injuries are coupled with dying roots and stem damage. Young plants and those with heavy damage to the stems may die after excessive fertilisation. To prevent a fertiliser injury, purchase a fertiliser recommended for azaleas. Apply the fertiliser lightly and evenly around the bush's drip line several times throughout the spring, plant pathologists D.M. Benson and Tom Creswell of North Carolina State University recommend. One large fertiliser application most commonly causes fertiliser injury.
A fungus known as Exobasidum vaccinii causes azalea bushes to develop leaf gall disease. The disease begins in the early spring, attacking new leaf growth. Leaves develop a thick, curled, flesh-like appearance. Over time, the leaves develop a powdery-white cover and eventually turn brown. Though leaf growth on a gall-infected azalea is unsightly, the disease is rarely serious. In most cases, azaleas recover from leaf gall with no fungicide treatment. Picking infected leaves off by hand and destroying them prevents the disease from spreading.
Attribute a reddish-brown leaf colour to the development of leaf rust disease. This disease is caused by the fungus Pucciniastrum vaccinii. The disease begins with leaves developing semicircular, yellow spots in the summer. As the disease progresses, orange or brown pustules develop. Clean up any infected leaves, as fungi spores will survive over the winter on dropped leaves. Hand-pick infected leaves to help prevent the spread of the spores. Rarely, heavily infested shrubs require fungicide treatment to survive a leaf rust infection.
Brown leaves, especially those turning brown on the tips, signify poor watering habits, according to the Azalea Society of America. Overwatering causes an azalea's root system to rot, which contributes to poor plant health. Nutrients from the soil are unable to travel up the damaged root system, and leaves begin to dry out and die. Brown leaves and wilting occur when an azalea is not receiving enough water. Soil that is moist to the touch is ideal, but standing water and puddles should be avoided. In dry weather, water plants with a deep watering. Water again when the soil begins to feel dry.