The American Phytopathological Society is reporting that bacterial leaf scorch (BLS) is becoming a greater concern among urban shade trees in many U.S. communities this year. More specifically, Ann Brooks Gould, associate extension specialist at Rutgers University, New Brunswick, N.J., tells Lawn & Landscape that BLS is a concern in the Eastern U.S. with more species affected in the southern states of the eastern seaboard and even as far inland as Texas.
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“Here in New Jersey, we’re seeing BLS on oaks, whereas in the Mid-Atlantic states it’s appearing on oaks, elms and sycamores,” Gould says. “Further south, more shade trees are affected and there are a number of tree species that are susceptible to the disease.”
Gould lists American elm, red maple, sweet gum, sycamore and London plane, and a number of oak species as susceptible to BLS. The disease has been found in landscapes, street plantings, and small woodlots in the affected region.
With an expertise in the New Jersey landscape, Gould says BLS affects as many as 35 percent of susceptible street and landscape oaks in some central New Jersey communities, and adds that this is a more severe impact than in years past. Current loss of value plus replacement costs for older trees affected by this disease is estimated at $8,000 per tree. Landowners and tree care professionals in these locations must plan for the loss of property values and high costs of replacement as shade trees in landscapes, wood lots and golf courses affected by BLS decline and must be removed.
BLS is caused by a bacterial pathogen, Xylella fastidiosa, which has a wide host range that includes common landscape ornamentals and weeds. X. fastidiosa is spread by insects, mainly sharpshooters.
Symptoms of BLS are very similar to those caused by environmental stresses. Because of this, the disease is often overlooked or misdiagnosed. On oak trees, BLS symptoms include scorching in late summer or early fall on leaves of all ages at about the same time. On sycamores and elms, symptoms progress from older to younger leaves. Affected leaves may curl and drop prematurely, and as the disease progresses, branches die and the tree declines. Elms may be killed outright by the disease. Other affected species eventually decline to the point where the dead branches pose a safety risk and the tree must be removed.
According to Gould, current management options of BLS in urban trees include:
- Maintain plant vigor. The development of BLS is enhanced by other diseases, insects, and environmental stresses such as drought. BLS may also predispose infected plants to other disease and insect problems.
- Practice sanitation. Branches that have died due to BLS should be routinely removed. Infected trees that are in a severe state of decline should also be removed.
- Use tolerant plants. In areas where BLS occurs, avoid planting highly susceptible trees, and design new tree plantings with a diverse complement of tree species.
- Replant around susceptible trees or trees in decline. As suggested by her colleague Dr. John Hartman the University of Kentucky, Gould says new and unaffected plants can be planted around trees in decline from BLS, so that when sick trees must be removed, there will still be some plant interest in the area.
More on the symptoms of BLS and disease management options is available in this month's APSnet feature article at http://www.apsnet.org/online/feature/bls/. APS is a non-profit, professional scientific organization. The research of the organization's 5,000 worldwide members advances the understanding of the science of plant pathology and its application to plant health.