Bacterial leaf scorch—or BLS—is a disease that affects many different kinds of trees, including several popular shade trees. Also called bacterial leaf spot, it can slowly kill a tree. The symptoms of BLS resemble those of drought stress, so it’s important to know the signs of this disease if you want to get ahead of it and save your tree. This article will:
- Educate you about the basics of bacterial leaf scorch
- Describe what symptoms to look out for
- Explain bacterial leaf scorch treatment
Bacterial Leaf Scorch 101?
BLS, one of many tree diseases, is actually a group of diseases caused by the bacteria Xylella fastidiosa. This bacteria lives in the water conducting tissues—or xylem tissues—of a tree. It then wreaks havoc, causing a number of problems. It'll kill a tree if it’s not kept in check.
The trees most susceptible to BLS include red maple, sweet gum, sycamore, and several species of oaks. It also affects many ornamental plants as well as food crops such as grapes, peaches, pecans, blueberries, and citrus.
Bacterial leaf scorch symptoms, and how it spreads
BLS causes two basic types of symptoms in the tree—leaf scorch and stunt. In shade trees, the symptoms are limited to leaf scorch.
It spreads from plant to plant though insects such as leafhoppers or sharpshooters. These insects drill small holes into the tree to feed on the fluid inside. If they have the bacteria on their bodies it can easily enter and infect the tree.
What does Bacterial Leaf Scorch look like?
When a tree has been infected with BLS the edges of the leaves become brown or “scorched.” Between the dead brown portion of the leaf and the live green tissue there is usually a yellow “halo.” This “halo” distinguishes BLS symptoms from those of environmental stress.
Leaves will fall from the tree long before normal fall leaf drop. The symptoms first appear in early summer and unfortunately, hot dry weather only exacerbates the symptoms.
The look of Bacterial leaf scorch only differs from other leaf scorches (caused environmental stress or a fungus) by the shape of the dead tissue on the leaves. The symptoms of BLS are so similar to those of environmental stress, that the disease is often overlooked.
Another way to identify BLS is to notice the random distribution of affected branches around the canopy. There may be a perfectly healthy branch next to one full of scorched leaves. The same is true for the population of trees in the landscape. There will be a few healthy trees between two trees infected with BLS. If you notice this seemingly random distribution of leaf scorch you can most likely rule out environmental stress.
Laboratory testing is the only sure way to confirm that a plant has BLS, but there are some clues to help tell the difference between drought stress and disease in your landscape. For plants infected with X. fastidiosa, the pattern of browning at the edge of the leaf is usually irregular.
Symptoms of BLS first appear in late summer to early fall. In trees such as oak, the scorching appears on leaves of all ages at about the same time. But in trees such as sycamore and elm, symptoms progress from older to younger leaves. Affected leaves may curl and drop prematurely, and as the disease progresses over several years, branches will die and the tree declines.
The disease may kill elms outright, while other affected species eventually decline to the point where the dead branches become dangerous and the tree must be removed. The process of tree decline may occur quickly or slowly, depending on the tree and the environment.
In addition to shade trees, BLS affects blueberries and pecans. The twigs and stems of young infected blueberry plants may look yellow. You will be able to see the yellow stems after the scorched leaves have fallen. Infected pecans show typical leaf scorch symptoms and will not produce as many nuts. The pecan kernels that are produced will be smaller than normal. Other important diseases caused by Xylella fastidiosa include Pierce’s disease of grapes, citrus variegated chlorosis, phony peach disease, and plum leaf scald.
Bacterial leaf scorch treatment
Unfortunately, there's no actual cure for BLS, but there are ways to increase your tree’s life span by years. A tree health specialist can apply an antibiotic tetracycline to an infected tree to alleviate symptoms. This treatment should be repeated every year, because symptoms reappear as the medicine breaks down in the tree.
bacterial leaf scorch control
In addition to treatment, the best way to help your infected trees is to keep them happy. Proper watering and fertilization in the spring will help keep your tree strong and may add years to its life. A healthy tree can sustain the infection better than an unhealthy one. A healthy tree is also less susceptible to other diseases, insects, and environmental stresses that enhance the development of BLS.
What you can do about bacterial leaf scorch
To control the spread of BLS, avoid planting highly susceptible trees in areas where BLS occurs. Those include red maple, sweet gum, flowering dogwood, sycamore, and several oaks. Popular oaks that are affected by BLS include bur oak, chestnut oak, live oak, Shumard oak, and willow oak..
Include a diversity of species when adding plants and trees to your landscape. This will reduce the spread of the disease by decreasing susceptible hosts. Planting a diversity of species also increases the value of your landscape to wildlife, pollinating insects, and is a good defense against losing a large number of plants to one disease.
And last, but not least
Always be a tree friend. Let your neighbors know if you see symptoms on their trees. Cheers.