Battling bacterial leaf scorch in shade trees


Shade trees are some of the most valuable landscape plants, and it is important to protect them. U of I Extension horticulture educator Ryan Pankau stopped by to tell us about one specific disease that is negatively impacting shade trees throughout the country.

Bacterial Leaf Scorch (BLS) is disease that impacts a number of native trees in our area, but it typically a primary issue of trees in the red oak subgenus, aka red oak group, most commonly impacting these urban trees:

  • Norther Red Oak
  • Pin Oak
  • Shingle Oak

Globally, this pathogen has started to spread and scientists predict it will continue to become a larger problem with climate change. The disease is caused by a bacterium, Xylella fastidiosa, and spreads by several pathways:

  • Insect transmission through leaf-feeding insects
  • Root grafts with infected trees 
  • Pruning cuts made with infected tools

BLS symptoms include:

  • Marginal leaf scorch, sometimes with a characteristic appearance 
  • See pic of brown leaf margin with colorful band, then green tissue along veins
  • Early leaf drop in late summer
  • Loss of tree vigor, less annual growth and often dieback of limbs

Diagnosis requires lab testing, it is important to correctly diagnosis this disease as the symptoms mimic drought stress and often appear at the same time of year. The University of Illinois Plant Clinic can test your tree if you think your Red Oak has symptoms. Contact the Plant Clinic for more details at:

There is currently no cure for BLS.  However, watering and mulching can extend the life of your tree. If your tree is negative for BLS, there are things we can do to prevent drought stress:

  • Watering during the stressful time of year
  • Extending mulched areas to the branch tips, or whatever is practical
  • Improve root zone soil conditions with practices to relieve soil compaction

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