Bacterial Leaf Scorch (BLS) is a chronic, infectious tree disease caused by the xylem-limited bacterium Xylella fastidiosa. It is transmitted by xylem feeding insects and colonizes the water transmitting tissue. Similar to the effects of Dutch elm disease it will physically clog the xylem, impairing the trees ability to conduct water from roots to crown. The tree’s natural combattant reaction to the presence and multiplication of this bacteria also clogs xylem, further hindering the transport of water to branches, leaves and crown. The systemic spread of bacteria and the effects thereof weaken and eventually kill the tree.
BLS is a disease of immense environmental, economic and aesthetic importance. Affecting urban trees such as sycamore, red maple, American elm, dogwood and many species of oak as well as agricultural crops like peaches, pears, coffee and grapes, this disease has a devastating effect on the community and economy. Spread by leafhoppers and treehoppers, it was originally thought that natural stands and environmental areas were not as badly affected as urban and managed areas, however, since 2001 BLS has been found in state parks and woodlands areas in New Jersey and Delaware resulting in mass die offs of native oak populations.
Afflicted trees exhibit marginal leaf necrosis bordered by a pale halo band separating the scorched from the green leaf tissue. Leaf discoloration moves from the margin to the midrib. Symptoms will recur and spread each year, taking over the crown causing stunted growth and dieback. Host plants are diverse and numerous including; red maple, American elm, sugar maple, sweetgum, sycamore, mulberry, red oak, turkey oak, pin oak and many other oak species. Some herbaceous and woody shrub species will have the disease but remain asymptomatic acting only as carriers.
This disease causes a distinct impact on communities affected due to high visibility specimens affected and agricultural losses. The disease is spread mainly through xylem-feeding insects, mostly members of the Cercopidae and Cicadellidae families, spittlebugs and leafhoppers, respectively. Some cases of root graft spreading have been reported. Treatment for leaf scorch currently only treats symptoms, and cultural techniques such as systematic pruning, proper watering and nutrient therapy may assist in the vigor and life extension for affected trees. Managing the spread of bacterial leaf scorch is complicated by the complex and varied life cycle of vectors as well as the potential reservoirs of disease available from infected asymptomatic species living alongside host species.
If you suspect any of your landscape trees is infected with BLS contact your arborist as soon as possible to develop a plan for treatment and management.