Bacterial Leaf Scorch

Xylella fastidiosa, “Xf” for short

Though fairly common in our area of southeastern PA, this disease is not thoroughly understood.  The bacterium is difficult to grow in a culture.  It has only been approximately two decades since an immune response (ELISA) test was developed that allowed accurate diagnosis.  Because the same symptoms – browning of leaves, starting at the margins, in late summer – can also be caused by environmental factors like drought, a certain diagnosis can not be made without a lab test.

My experience with this disease dates to 1992, the first year I began having samples tested with the reliable immune-response procedure.  Since then, I have been monitoring the health of trees that have been diagnosed with Xf.  Some clients have opted to treat trees with Oxytetracycline, others to do nothing.  Here are some of my observations from the last 16 years of monitoring specific Xf positive trees:

Currently, the primary research on Xylella is being done at Rutgers University in New Jersey by a team lead by Dr. Ann Gould, so I’ll let Dr. Gould tell you about the disease with this link:  Bacterial Leaf Scorch

For a more in-depth study, you can go here:  Bacterial Leaf Scorch of Amenity Trees

More research is needed.  The Rutgers project is being partially funded by contributions from members of the Penn-Del chapter of the ISA*.  See more about our fundraising here (page 14 of December 2007 newsletter):  Penn-Del ISA Newsletter

*ISA is the International Society of Arboriculture – the professional society for arborists.  See and


If your tree tests positive for Xf, you may wonder what you should do.  Here are my suggestions: