Singed brown edges on leaves of trees are called scorch. This can be caused by different types of stress such as drought, root growth restriction, compacted soil or even salt damage. Oak Wilt is a disease which also causes browning of the tree leaves. Bacterial Leaf Scorch (BLS) is a disease which infects Oak trees as well as Maples, Lindens, Elms and others, although it is more commonly found in Oaks, especially Red Oaks. Leafhoppers, spittle bugs and other Xylem feeding insects carry the bacteria from tree to tree.
This pathogen blocks the flow of water and nutrients to the leaves which causes the scorched leaf effect. Leaves of trees infected with BLS develop normally in the spring but start to show signs of scorching by August or September. This disease causes the margins (outside edges) of the leaves to turn brown. Unlike with Oak Wilt, when trees are infected with Bacterial Leaf Scorch there is often a yellow, or reddish band between the green leaf center and it’s brown margin. Quite often the effected leaves will drop prematurely in the early fall. These symptoms worsen during drought conditions. When a tree first becomes infected with BLS, only a few branches of scorched leaves may be seen. As this disease progresses, it gradually spreads throughout the tree. Smaller branches will die first, and within a few years, larger and larger limbs will die. Bacterial Leaf Scorch, if left untreated, will slowly kill the tree.
Oak or other trees showing signs of BLS should be protected from stress whenever possible, such as watering in times of drought. To save trees infected with Bacterial Leaf Scorch it is important to start treating before the disease has progressed to an advanced stage. This pathogen can never be cured, but if caught in time, and treated annually with systemic Oxytetracyclin injections by a certified applicator, it can be effectively suppressed. If treatment is not begun in the early stages of disease development, Paclobutrazol (PBZ) injections have also been shown to help reduce Bacterial Leaf Scorch. PBZ is a plant growth regulator which inhibits synthesis of the plant hormone gibberellin. This chemical suppresses shoot growth and stimulates root development which helps reduce symptoms of bacterial leaf scorch.