Pin Oaks & Sycamores; Scorched Leaves in Late Summer/Early Fall
If you’ve noticed the leaves of your pin oaks & sycamores turning partially brown late summer/early fall, this is not normal. You may have a serious problem.
The Signs & Symptoms
It can look like a mischievous boy has painted the bottom half of your green pin oak leaves brown (A). While sycamore leaves just start crinkling up (B). Though it may start with some of the lower branches, it eventually spreads to the whole tree.
Then, smaller dead branches start to appear, and eventually larger. While it went unnoticed in October, as the disease progresses each year, it creeps into September, and eventually into August. Each year leaf drop occurs earlier. As the tree starts to decline, other pests attack. What is going on?
Your trees may have Bacterial Leaf Scorch (BLS).
How it is Spread
BLS is caused by the bacterium Xylella fastidiosa, and spread by leaf hoppers & spittlebugs, as they feed upon succulent, terminal shoots of susceptible host trees.
The Damage it Causes
Xylem water-conducting vessels become clogged with the bacterium as it travels within, multiplying & infesting other parts of the tree. The bacterium overwinters & keeps clogging more vessels each year. Though it goes mostly unnoticed,. BLS is probably our most devastating tree pest in the Upstate.
While all shade trees are vulnerable, sycamores & pin oaks seem to be the hardest hit; followed by red oaks, white oaks, maples, sweetgum, elms & mulberries.
While arborists that have worked with this pest for many years can usually ID BLS by symptoms alone, since treatment can be expensive, it makes sense to have fall samples tested in a lab (Clemson University).
1. Maintain plant vigor. Keeping susceptible trees healthy can help them resist infection & survive longer once they become infected. This can be done through proper mulching (1 to 2 inches of aged, all-tree wood-chip mulch 8 to 10 feet out from the root flares), watering (especially during the dry weeks of late summer & early fall), and fertilization (only if needed, and after a soil test).
2. Pruning. Branches that have died due to BLS should be routinely removed. Trees that have more dead than live branches can serve as brood trees & spread infection to other trees, and should be removed.
3. Treatment. While there is no cure for BLS, antibiotic injections, and growth regulators have been found to extend the life of infected trees (if you don’t wait until it’s too late). But this can be expensive & must be continued every year. Improper application can invite more pests, spread decay & reduce the water-conducting capability of your tree. There is some wounding even with proper installation (C). But this can be an acceptable tradeoff, when faced with loosing large shade trees. Of course, the best policy is to keep your trees healthy, so they’re less susceptible to pests like BLS.
4. Replacement. Severely declined shade trees should be removed due to safety concerns & spreading disease to other trees. Consider planting species that are less susceptible to BLS (see our Tree Selection page under Plant).