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How To Identify And Treat Bacterial Leaf Scorch In Oak Trees

bacterial leaf scorch oak tree

As its name suggests, bacterial leaf scorch is bad news for your trees.

This is a systemic disease caused by the bacterium Xyella fastidiosa, which infects the xylem – the tissue that transmits water and nutrients – of trees.

While it’s most common in different varieties of oak trees, BLS also affects ash, elm, red and sugar maple, mulberry, sweetgum and sycamore trees. The bacterium is spread by xylem-feeding insects as they travel from tree to tree, and by root grafts.

BLS has no known cure. It is a chronic and potentially deadly disease.

How do I know if my trees have bacterial leaf scorch?

The only way to be sure a tree has bacterial leaf scorch is through a laboratory analysis. The best time to test is during late summer or early autumn when the bacterial count is at its peak.

The first sign a tree has BLS is leaves that get brown in mid-summer. The symptoms then worsen during the late summer and fall, with leaf margins turning brown, beginning with older leaves and moving outward. In most trees, the brown area of the leaf is separated from the healthy green section by a yellow border.

In the years after BLS first presents, your tree will leaf out as usual, but more and more leaves will turn brown prematurely. This will continue over the next three to eight years until the whole tree begins to turn brown prematurely. Without healthy green leaves producing chlorophyll, the trees twigs, branches and limbs will begin to die.

According to the Missouri Botanical Gardens, BLS can be mistaken for oak wilt and Dutch elm disease. Here’s how to tell the difference:

  • BLS repeats its cycle and gets worse over a long period. Oak wilt and Dutch elm can kill trees within a few months.
  • With BLS, there is no streaking of sapwood.
  • Leaf browning in oak wilt and Dutch elm disease typically happens in an overall, uniform manner. With BLS, the browning develops at the edge of the leaf and works its way in.

It’s also possible to mistake BLS for drought or heat stress. But again, BLS begins in older leaves and spreads to branch tips, whereas environmental stresses cause an overall browning.

How is BLS transmitted?

A BLS infection is thought to begin with insects – leafhoppers and spittlebugs – that feed on susceptible host trees, transmitting the bacteria. The xylem vessels in the tree become choked with the bacterium, which multiples and infects other parts of the tree.

How can I help my trees?

While there is no cure for BLS, there are steps you can take to keep your trees healthy.

  1. Trees work the same way we do. When we’re healthy, we’re less susceptible to getting a cold or the flu. And if you keep your trees healthy, they’ll be able to resist infections and last longer if and when they do become infected with BLS.
  2. Check with an arborist to learn whether BLS has occurred in your area. If so, avoid planting trees that are susceptible to infection.
  3. If you have branches that have died, be sure to make a practice of pruning them. Trees in the later stages of infection should be removed outright.
  4. Antibiotic treatments can reduce bacteria levels and hold off symptoms of BLS for a few weeks. These tree treatments are not a cure and need to be reapplied every year. This is something a certified arborist can help you with.

If you have trees that you’re worried about, contact Willow Tree and Landscape Services. Our plant health care services are committed to keeping the trees and shrubs on your property vital and beautiful. Whether it’s preventive care or timely tree treatments, our certified arborists have the expertise to protect your trees from BLS and other illnesses.