Bacterial leaf scorch is an important disease of shade trees that is caused by the xylem-inhabiting bacteria Xylella fastidiosa. It has been reported as far north on the eastern seaboard as New York and is prevalent in the southeast, Texas, and extends northward to Illinois. Commonly infected trees include elms, sycamores, maples, and a number of species of oak.
Bacterial leaf scorch is a frustrating problem because there is no known cure. Infected trees die prematurely and their appearance deteriorates over their lifespan. A variety of management practices are aimed at extending the longevity of infected trees. These include treatment with Bacastat, water stress reduction through mulching, irrigation, and the use of Cambistat and control of the leafhoppers and secondary insects with Transtect or Xytect. Trees killed by bacterial leaf scorch should be replaced with species that are not susceptible to the disease.
Other Treatment Practices
- BLS is included on the Cambistat label. Results with Cambistat as a stand-alone treatment for bacterial leaf scorch have been variable, but generally beneficial.
- Bacastat should be included with other sound cultural practices such as mulching, supplemental irrigation during dry periods, and other insect and disease management practices.
- Rainbow’s Root Enhancement system is a good treatment for trees affected with BLS.
- Macro-infusion treatments have performed equally as well as micro-infusion treatments.
- For annual suppression of scorch symptoms during the year of treatment.
- If treatments are not done annually, scorch symptoms will reoccur.
- Data from trials have shown up to 85 % suppression of scorch symptoms.
Signs of Damage
- Leaves develop normally early in the season and symptom expression begins in June and Julyand peaks in August and September
- Necrosis begins along the leaf margin and spreads toward the veins and petiole in an irregular pattern
- Green tissue is separated from necrotic tissue by band or halo of yellow or reddish brown bands
- Symptoms may occur initially in one area of the crown and in severe cases the whole canopy may be affected
- Scorch symptoms will reappear in the same limbs from one year to another and may spread to other limbs
- Severely scorched leaves may curl or roll
- Symptom severity may vary from one year to another
- Marginal reddening or yellowing followed by browning of leaves
- Premature death
- Scorch develops first on older leaves and progresses toward the tip
Trees At Risk
- Red oak (Quercus rubra)
- Pin oak (Q. palustris)
- Bur oak (Q. macrocarpa)
- Red maple (Acer rubrum)
- Americanelm (Ulmus Americana)
- Sycamore (Platanus occidentalis).
- Bacterial leaf scorch is spread by xylem feeding insect vectors including sharpshooters, treehoppers, leafhoppers, and spittlebugs.
- Much is still unknown about this disease.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.