Key points
- Bacterial leaf scorch (Xylella fastidiosa) is a disease of shade trees in Maryland. It affects a large number of shade trees including elm, catalpa, hackberry, ginkgo, oak, sycamore, maple, mulberry, and sweetgum in the landscape.
- Depending on the severity, this disease can cause tree death.
- The pathogen is a bacterium that grows inside the plant’s vascular tissue where it blocks water movement from the roots.
Symptoms of bacterial leaf scorch (BLS)
- Symptoms will occur every year and progress through the crown (top of tree).
- Scorched areas may have a yellow halo around them depending on the tree species.
- Reduced growth and dieback are also common in severely infected plants.
- These symptoms are sometimes mistaken for drought, environmental stress, or root diseases.
- Bacterial scorch symptoms differ from drought scorch symptoms. BLS symptoms first appear on the lower branches and on the older interior leaves. Drought scorch symptoms will be more uniform and will first appear near the upper branches and on the younger leaves near the tips of the branches.
- Symptoms typically appear in mid to late summer on lower branches as irregular marginal browning on interior leaves. Symptoms progress along the branch towards the tip.
- The organism, Xylella fastidiosa, is a small gram negative bacterium with no flagella. It doesn’t form resting spores, has a thick rippled cell wall, and does not grow on conventional bacteriological media. This bacterium is spread by planthoppers called sharpshooters, treehoppers, and spittlebugs that feed on infected plants and after feeding, the bacterium will spread systemically through the vascular system.
Management of bacterial leaf scorch
There are no treatments for bacterial leaf scorch. However, infected trees may continue to persist in the landscape if symptomatic branches and dead wood is pruned out promptly. Antibiotic trunk injections, administered by a licensed arborist, have shown promise but they only relieve symptoms and don’t provide a cure.