Bacterial Leaf Scorch (BLS): Key Facts
Bacterial Leaf Scorch
One of the more common tree diseases you might see on your oak, sycamore, or elm is bacterial leaf scorch. The symptoms of this infection are most noticeable towards the end of summer and beginning of fall throughout the southern and eastern US, and it may be mistaken for a lack of water because it shows up on the leaves of infected trees as crispy, brown edges. This is because the bacteria affects the tree’s ability to process water, which starves the extremities. Here, we’ll go over how bacterial leaf scorch is spread, how to identify it, and what can be done to control an infection.
How Does a Tree Get Infected With Bacterial Leaf Scorch?
The disease is spread by the sharpshooter insect, a leafhopper that feeds on the sap of trees and other plants. These bugs may be carrying the bacteria in their saliva, which doesn’t harm them but will infect and spread throughout a tree’s internal water circulation system (the xylem). The bacteria then grow in the tree’s tissue and build up, blocking the movement of water and nutrients in a tree. In addition, the damage to the leaves prevents photosynthesis, which decreases the available energy to the tree and further damages its health.
Bacterial leaf scorch shows up on the leaves of a tree, but it also affects whole branches once the tree’s tissue vessels are blocked. Since it’s spread by an insect and then circulated by the tree’s internal system, it can show up anywhere on a tree and is difficult to prevent.
What Are the Characteristics of Bacterial Leaf Scorch?
When a tree contracts bacterial leaf scorch, the main sign of infection is that leaves will turn brown off-season, usually towards the end of summer and beginning of fall, when leaves should be green or their normal autumnal shades of red, orange, or yellow. It usually affects the interior leaves of a tree first, working its way from those closest to the trunk outwards. On the individual leaves, the browning will begin at the edges and spread to the interior of the leaf, usually with a yellow band between the healthy part of the leaf and the dead tissue. In general, the patterns will be irregular and scattered.
While bacterial leaf scorch usually only affects oaks, elms, and sycamores, it’s a non-selective disease that has the potential to affect any other tree, although it’s much less common. On any given tree, the main signs of a leaf scorch infection include:
Off-season leaf death with scorched appearance
Early leaf drop
Branch death
Once symptoms start to show, tree owners have to be discerning not to mistake it for dehydration since overwatering a tree can result in more stress in addition to the infection. While drought and dehydration can make the problem worse, a tree that’s showing scorched-looking leaves despite plenty of rain or watering should be checked out by a certified professional to test for the bacteria, which is the only way to confirm an infection. Once the presence is confirmed, there are some options for bacterial leaf scorch treatment, but there is no definitive cure for the disease.
How Do You Control Bacterial Leaf Scorch?
While there is no cure for bacterial leaf scorch, there are treatments that a certified arborist can apply to prolong the tree’s life. It should be diagnosed in late summer or early fall when it is visible, and a lab test will confirm the infection. If leaf scorch is confirmed, there are a few options available to manage the infection and prevent spread to nearby trees.
One way to help control or prevent spread to nearby trees is by removing the infected leaves when they drop. They shouldn’t be added to compost or mulch since the bacteria will sit dormant and can easily infect another tree when that organic matter is applied elsewhere. Infected leaves should be thrown away (leaf burning is illegal in Nashville) so they will be removed from the ecosystem entirely.
To treat an infected tree and extend its life, a tree care professional may apply yearly treatments of an antibiotic that will suppress as much of the bacterial growth as possible. This, in addition to good fertilization and regular watering, will keep the tree in a healthy condition so it can defend itself against the infection. Depending on the extent of the infection, treatment may or may not be recommended by a professional, although in the best cases, antibiotics may extend the life of a tree for another five to ten years.
Sometimes, treatment for bacterial leaf scorch may not be effective enough to save the tree, and removal may be suggested. If there is a lot of dieback, or if treatment doesn’t seem to be working, an infected tree may be a hazard for other trees. In any case, a tree care professional will recommend the best course of action and will help you understand the available options to treat, remove, and replace your tree.
While maintaining trees in healthy condition is essential for a mature, productive neighborhood canopy, planting a new tree when one dies is important to keep the cycle going. Browse our tree sale for your tree-planting needs, and consider volunteering with us to help plant new trees across the city of Nashville. To stay informed on best practices for tree care and other arboreal information, sign up for our newsletter!