Bacterial Leaf Scorch (BLS) is a bacterial plant disease of major environmental, economic, and aesthetic importance. Urban trees such as sycamore, red maple, dogwood, American elm, several species of oak and agricultural crops such as plura, peach, pear, coffee, and grapes can become infected and eventually die. This disease is caused by a vascular clogging bacterium (Xylella fastidiosa) that multiplies rapidly within active plant xylem. Distinct scorch-like leaf symptoms are followed by twig and branch death leading to plant decline and death. Many other plants such as numerous shrub species and grasses become infected with BLS, but do not show symptoms and do not die. Knowledge of BLS presently is limited especially when attempting to understand how infection is contracted and spread within the urban environment. What is known is that the BLS bacterium is spread from diseased to healthy plant material during feeding by common urban xylem-feeding insects such as leafhoppers and treehoppers.
The disease was thought not to have significant impact in forests compared to urban environments where tree stress factors and insect vectors are distinct. However, in 2001 BLS was discovered in a New Jersey woodland area and in 2003 within the Parvin State Forest. Since this time, investigations document increasing numbers of oaks in New Jersey forested lands dying from BLS.
An ongoing survey in Delaware, conducted by the Delaware Forest Service, also collects data that describes the spread and number of dying oaks within the Blackbird State Forest.
Another study in a southern New Jersey forest conducted by the New Jersey Forest Service presently is documenting the incidence of this disease. The study also seeks to describe the effects of applying a standard silvicultural technique to determine if the disease can be abated within the forest. Samples collected from both these studies are analyzed for the causal organism (Xylella fastidiosa) by the Rutgers University Plant Pathology Diagnostic Laboratory, New Brunswick, NJ using enzyme-linked immuno sorbent assay (ELISA) and polymerase chain reaction (PCR) analyses.
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Website Contact: Alan Iskra, Forest Pathologist, USDA Forest Service.