Bacterial Leaf Scorch Affects New Jersey State Tree

Symptoms on the state tree, the Red Oak in Moorestown, New Jersey. (Photo courtesy of the New Jersey Community Forestry Program).

The New Jersey Forest Service Community Forestry Program, with oversight by the New Jersey Community Forestry Council, conducted a statewide survey for Bacterial Leaf Scorch (BLS) in oaks in the summer/fall of 2001. The survey was funded by a $95,000 state appropriation (P.L. 2001, c. 8), which was sponsored by State Senator Martha Bark and State Assemblymen Francis Bodine and Larry Chatzidakis. The goal of the survey was to determine the spread and impact of BLS on New Jersey's oak tree population, as well as to increase public awareness of this growing disease problem in New Jersey's tree resource. The survey and report are now complete, and the results indicate that BLS is indeed a serious threat to New Jersey's trees.

• 533 out of the 1,372 oaks sampled tested positive for Bacterial Leaf Scorch infection; this is 39% of the samples taken statewide.
• 61% or greater positive sample results were found in samples taken in Mercer, Burlington, Camden Gloucester, Salem, and Cumberland Counties.
• 233 of the 533 oaks that tested positive for Bacterial Leaf Scorch (44%) are over 20 inches in diameter.
• The economic impact of this disease could be devastating to municipal budgets in New Jersey municipalities, as trees will need to be pruned and in many cases removed to address potential hazards caused by the disease.
• The aesthetic impact of this disease will also be felt throughout New Jersey's affected municipalities, as large tree removals will change the character of neighborhoods, and replacement trees will take decades to grow to the size of the trees that were removed.
• Bacterial Leaf Scorch is not just a street tree problem, in the future traditional forests should also be surveyed, sampled and monitored for this disease.

BLS is caused by the bacterium Xylella fastidiosa. BLS affects the xylem, which are the cells that transport water between the roots and the leaves of a tree. The bacteria live and multiply in the xylem vessels of the tree, clogging the xylem and disrupting the conduction of water within the tree, causing the leaves to scorch. The presence of the bacteria may also trigger a reaction in the tree that plugs the xylem, further impeding water transport. Leaf scorch eventually leads to branch dieback. The overall decline of an affected tree can last for several years, but will eventually lead to tree mortality. The symptoms of BLS in New Jersey oaks are only visible for a few weeks in mid-summer and early fall, and are easily confused with scorch caused by drought stress and other abiotic or non-biological stresses, as well as the change to autumn color. In affected leaves, the outer edges of the leaf will begin to turn brown, with the discoloration moving toward the center of the leaf in an irregular pattern. Perhaps the most distinguishing visible characteristic of BLS in oaks is that the affected leaf will present a "water-soaked" region, sometimes a red band, and sometimes a yellow halo at the transitional area between the browning portion and the healthy green portion of the leaf. BLS may be localized to one area of the tree before spreading throughout the tree, or may seem to attack the entire tree at once, exhibiting symptoms throughout the crown. Affected branches may refoliate for several years, but will continue to be symptomatic, and will eventually result in branch dieback. Many of the symptomatic leaves remain on the tree until normal autumn defoliation, however several will fall to the ground early, which is another indicator of BLS. A tree can harbor a BLS infection for several years, but eventually the stress of the disease and the resulting branch dieback will lead to secondary pathogens or insects, speeding the decline of the tree. This can create potentially hazardous situations, making tree removal necessary. BLS is believed to be spread by xylem feeding insects, such as leafhoppers, treehoppers and spittle bugs. These insects spread BLS by feeding on the xylem fluid of an infected plant, thus picking up the bacteria, and then injecting the bacteria into the xylem cells of healthy plant leaves when they feed on uninfected trees. The disease is not only transmitted from already affected trees, but can also be spread from other plants that these insects feed on, such as goldenrod, blackberry and alfalfa, which are expected to be carriers of Xylella fastidiosa. It has not yet been determined if the bacteria can be spread through root grafts or by pruning tools.

Severely infected Pin Oak in Moorestown, New Jersey. (Photo courtesy of the New Jersey Community Forestry Program).

What Can Be Done? Currently, there is no known cure for BLS. Injecting diseased trees with antibiotics can suppress symptom development, but cannot eliminate the pathogen, and injections are expensive and must be repeated yearly, which puts an additional stress on affected trees because it creates several new wounds each year. Antibiotic trunk injections have been used with marginal success and at great cost, and in most cases these treatments are impractical. For now, the New Jersey Forest Service recommends that you water affected trees and prune off affected branches. Affected branches should be removed well below the symptomatic leaves. Beyond this the New Jersey Forest Service encourages residents to be aware of this disease, monitor their own trees for it, and seek advice from a New Jersey Certified Tree Expert or Approved Forester for pruning and removal needs. This survey work indicated that there is widespread interest and support for the project from residents of New Jersey, who throughout the survey showed concern for their trees and willingness to help. There is also a great need for research, monitoring, treatment and education and awareness to continue in order to find a way to stop the spread of this disease in New Jersey's oaks. The New Jersey Forest Service will continue to seek funding and support from the state legislature and other organizations in order to make this possible. For additional information contact: USDA Forest Service: Alan Iskra (304) 285-1541 or e-mail: aiskra@fs.fed.us NJ Forest Service: (609) 292-2532. To request a copy of the complete New Jersey Bacterial Leaf Scorch Survey Report (P.L. 2001, c. 8), contact the NJ Forest Service.