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by Scott Diffenderfer

Why are my tree’s leaves turning brown in late summer? Bacterial Leaf Scorch (Xylella fastidiosa) may be to blame. A disease of deciduous trees in Maryland and Virginia, it affects a large number of shade trees. These include elm, catalpa, hackberry, gingko, oak, sycamore, maple, mulberry, and sweetgum.  Most cases of Bacterial Leaf Scorch (BLS) are found on oaks in the suburban Maryland and Metro DC locations serviced by Mead Tree & Turf Care.

Symptoms of Bacterial Leaf Scorch

Symptoms of Bacterial Leaf Scorch (BLS) typically appear in mid to late summer on lower branches, as irregular marginal browning on interior leaves and progress along the branch towards the tip. Other characteristics include:

  • Symptoms that occur every year and progress through the crown (top of tree).
  • Scorched areas with a yellow halo around them depending on the tree species.
  • Reduced growth and dieback in severely infected plants.
  • Symptoms that are sometimes mistaken for drought, environmental stress, or root diseases.  Enhanced leaf browning and discoloration is typical after a period of late summer drought, such as we had this year.
  • Bacterial scorch symptoms differ from drought scorch symptoms.  Leaf scorch symptoms first appear on the lower branches and on the older interior leaves.  Drought scorch symptoms are uniform and first appear near the upper branches and on the younger leaves near the tips of the branches.

In this picture, the tree at the right is infected with BLS. The one at the left does not show symptoms, although it is most likely infected.

Tree on right with visible symptoms
Close up view

Facts about Bacterial Leaf Scorch

  • The pathogen is a small bacterium, Xylella fastidiosa. It grows inside the plant’s vascular tissue where it blocks water movement from the roots. It does not form resting spores, has a thick rippled cell wall, and does not grow on conventional bacteriological media. 
  • Several types of plant hoppers such as sharpshooters, treehoppers, and spittlebugs spread this bacterium.  These insects feed on infected plants. They then move to another site and infect that leaf tissue when they feed.  After feeding, the bacterium spread systemically through the vascular system. 

Management of Bacterial Leaf Scorch

BLS will greatly reduce tree vigor when not managed. Even with a proper management program, the disease is never completely controlled. Trees not managed for BLS will decline slowly over course of 8 to 10 years. 

  • Antibiotic trunk injections, administered by a licensed arborist, have shown promise but they only relieve symptoms and do not provide a cure.
  • Tree fertilization can help contribute to the overall health of the tree.
  • Prompt removal of symptomatic branches and dead wood may help reduce the chance of infected trees continuing to persist in the landscape.

Call Mead Tree & Turf Care to arrange for an arborist to evaluate your trees for BLS and to develop a care plan.

Resources:

https://www.fs.usda.gov/naspf/sites/default/files/publications/bls_amenity_trees.pdf

https://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/non_HGIC_FS/Bacterial%20Leaf%20Scorch%20web.pdf

https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/3001/3001-1433/SPES-83NP.pdf

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