Arbor Business: The BLS Blues

Over the last 10 to 15 years, Bacterial Leaf Scorch (BLS) has been observed from southern New York to Florida. Since the disease is considered young, there is still research being done, however, it is important to recognize what we do know, as well as identify proper management practices. BLS threatens several species of oaks, such as the northern red oak, pin and scarlet oaks, as well as other urban trees such as sycamore and elm.

BLS is caused by the bacterium Xylella fastidiosa, which actually clogs the tree’s xylem, or water conducting tissues. This stresses the tree by disrupting water absorption and inhibiting the transport of water to the roots, branches and leaves.

The bacterium is transmitted to healthy trees by spittlebugs and leafhoppers – insects that feed on the xylem. Further research is being conducted to detect other xylem-feeding insects that may also carry the bacterium. The insects acquire the bacterium when feeding on other infected trees and many herbaceous plants and riparian weeds that contain the bacterium. These riparian weeds, most commonly found along bodies of water, serve as an alternate host for the bacterium. The xylem-feeding insects then infect the host. The most recent research has ound a higher concentration of BLS along rivers and streams, yet BLS is still a widespread disease.

The only way to positively identify the bacterium in the vascular tissue is to detect it through microscopic tests. However, there are symptoms you can look for to identify the presence of BLS. Symptoms appear mid-summer and continue through fall. Leaves on infected trees will begin to dry along the margins and progress towards the middle of the leaf. There is a very blatant distinction between the infected and healthy tissues of the leaf. Finally, the entire leaf will turn brown and die.

Throughout the first few years of infection, only isolated branches will be affected. Over the course of time, the bacteria will move throughout the entire crown of the tree. Typically, depending upon the size of the tree, it will decline over a four- to 10-year time span. The size of the tree and management practices will determine how well it withstands BLS.

Currently, there is no known cure for BLS. Injecting trees with antibiotics can help slow down the disease’s development, but this will not eradicate the pathogen. This can be a costly protocol and must be done every year. Further research is being conducted to determine this method’s efficiency. It has also been noted that even distribution of the antibiotic has been inconsistent.

The best BLS management practices include removal of infected branches, proper watering and mulching the tree correctly to reduce drought stress. There is no evidence of the disease moving from tree to tree. Therefore, removal of a tree at the first signs of BLS is fruitless. Instead, protect the tree from drought stress, but don’t remove it unless the tree becomes a hazard.

No research has been done on whether fertilization benefits trees stricken with BLS. High nitrogen fertilizers will force new succulent growth, making the tree more attractive for xylem-feeding insects. Studies are being conducted on the impact of high and low nitrogen fertilizers and their role in BLS.

BLS is a problem throughout the landscape that needs to be addressed. Until further research develops a cure, responsible professionals can be aware of the symptoms and signs of BLS and educate the public on how it can be properly managed. – Mike Sisti

The author is owner of Alpine Lawn & Tree Care in Freehold, N.J., and can be reached at 732/625-3929 or alpine@optonline.net.