A problem that seems to be an increasing across the area with oak trees is Bacterial Leaf Scorch. Up until about 2012 or so, this disease was considered a minor problem that oak trees typically overcame. Here recently, this disease is causing a slow decline of our older oak trees once they become infected.
What do the symptoms look like? The first noticeable symptom is premature browning of leaves in mid-summer. Symptoms worsen throughout late summer and fall. Leaf margins turn brown, beginning with the older leaves and moving outward, spreading to leaves toward the branch tip.
The only way to confirm the diagnosis of bacterial leaf scorch is through laboratory analysis. This can be done by sending a sample to the University of Illinois Plant Clinic. The best time to test for the presence of this disease is in late summer or early fall, when the bacteria count is at its highest.
This disease is transmitted by leafhoppers and spittle bugs, when they feed on the succulent, terminal shoots of susceptible host trees, transmitting the bacteria. The xylem vessels become clogged with bacterium as it travels within, multiplying and infecting other parts of the tree. There are no viable control options for the insect vectors. The cold-sensitive bacteria overwinter in protected areas within the xylem of the tree, and their populations begin to climb again as the next growing season progresses.