Bacterial Leaf Scorch
Discovered in New Jersey in the early 1990’s, Bacterial Leaf Scorch (BLS) is a vascular disease that can infect many common landscape trees. The bacteria associated with BLS clogs up the water-conducting tissues (xylem) in a tree. This causes the tree to appear to be under water stress.
A number of xylem-feeding insects, including leafhoppers and treehoppers, move Bacterial Leaf Scorch from infected trees to healthy trees. The gradual decline that follows infection causes host trees to become unsightly and unsafe.
Bacterial Leaf Scorch has been found in California, Illinois, Indiana, Kentucky, Nebraska, New York, Ohio, Texas, and Washington, DC. It is probable that BLS is waiting to be confirmed in several other states, as well.
TREES INFECTED BY BACTERIAL LEAF SCORCH
The list of trees that are susceptible to Bacterial Leaf Scorch is long. Common landscape trees that can be infected by BLS include:
American Elm (Ulmus americana)
Bur Oak (Quercus macrocarpa)
Chestnut Oak (Quercus prinus)
Ginkgo (Ginkgo biloba)
Hackberry (Celtis occidentalis)
Laurel Oak (Quercus laurifolia)
Live Oak (Quercus virginiana)
London Planetree (Platanus acerifolia)
Pin Oak (Quercus palustris)
Post Oak (Quercus stellata)
Red Maple (Acer rubrum)
Red Oak (Quercus rubra)
Scarlet Oak (Quercus coccinia)
Shingle Oak (Quercus imbricaria)
Silver Maple (Acer saccharinum)
Sugar Maple (Acer saccharum)
Sycamore (Platanus occidentalis)
Sweetgum (Liquidambar styraciflua)
Water Oak (Quercus nigra)
White Oak (Quercus alba)
Willow Oak (Quercus phellos)
SYMPTOMS OF BACTERIAL LEAF SCORCH INFECTION
The symptoms of BLS usually become apparent in late summer and continue throughout the fall. Leaf browning begins at the edge of the leaves, while the leaf tissue closest to the mid-vein remains green. The area between the brown and green leaf tissue is often separated by a yellow band. The yellow band is not always present on BLS infected trees and on Pin Oak (Quercus palustris) the marginal leaf browning may not occur at all, but the leaves will drop sooner than normal.
The symptoms of Bacterial Leaf Scorch usually shows up on one or two branches and spreads to more branches each year. This is followed first by twig dieback and then the death of entire branches.
HOW TO CONTROL BACTERIAL LEAF SCORCH
At this time there is no known preventative or curative treatments are available for Bacterial Leaf Scorch. Pruning can keep the appearance of some trees acceptable, but as the disease progresses through the tree the aesthetic quality of the tree will decline and eventually the tree will be lost.
Providing supplemental irrigation to trees during the summer will reduce moisture stress and may delay the development of BLS symptoms. Mulching under the canopy of the infected tree will also help to maintain soil moisture levels. Fertilizing can be done if soil or leaf analysis indicates a nutrient deficiency.
Annual trunk injections of antibiotics in late May or June have suppressed the symptoms of Bacterial Leaf Scorch, but have not been shown to cure trees of the disease.
At some point tree replacement will be necessary for trees infected with Bacterial Leaf Scorch. Trees that could be used to replace BLS infected trees include:
Yellow Buckeye (Aesculus flava)
European Black Alder (Alnus glutinosa)
Northern Catalpa (Catalpa speciosa)
Katsuratree (Cercidiphyllum japonicum)
European Beech (Fagus sylvatica)
Kentucky Coffeetree (Gymnocladus dioicus)
Tulip Poplar (Liriodendron tulipifera)
Osage Orange (Maclura pomifera)
Cucumbertree (Magnolia acuminata)
Black Gum (Nyssa sylvatica)
American Linden (Tilia americana)
Littleleaf Linden (Tilia cordata)
Silver Linden (Tilia tomentosa)
Japanese Zelkova (Zelkova serrata)