Bacterial leaf scorch
IDENTIFICATION — You wouldn’t be surprised to find a few brown leaves on a tree near the end of summer. But take a close look: Do the leaves have an irregular pattern of browning with a pale yellow or red band between the brown and healthy green leaf tissue? If so, it could be bacterial leaf scorch. This disease, caused by the bacterium Xylella fastidiosa, clogs the plant’s water-conducting tissues. It’s spread by spittlebugs, leafhoppers and treehoppers as they feed and is mostly confined to the Eastern and Southern United States. Sycamore, mulberry, maple, dogwood, American elm and several species of oak trees are affected.
DAMAGE — Symptoms start showing up in early summer and get worse by autumn. Each tree species is affected a little differently, but generally you’ll notice premature browning, or scorching, of leaves first. As browning spreads toward the middle of the leaf, the edges curl in and the leaf may drop off the tree. Each year more leaves turn brown. Then twigs and whole branches start to die and growth is stunted. Once weakened by this, the tree becomes vulnerable to other infections or infestations. It can take as long as five to 10 years for the whole tree to die.
CONTROL — There’s no cure for bacterial leaf scorch. It can usually be diagnosed by symptoms alone but for a definitive diagnosis, check with your local extension agency. If you need time to select and plant a new tree, you can keep the old tree going by hiring an arborist to administer trunk injections to suppress the symptoms. Or delay the development of the disease by removing infected limbs and avoiding drought stress. Mulching around the tree and watering during dry spells will help keep moisture even. Whatever treatment you choose, the tree will eventually need to be removed.