All over central Kentucky, ornamental pin oaks are in trouble. They are slowly declining and dying, and looking terrible in the process. From street trees to horse farms, thousands of pin oaks need to be removed over the next few years. The primary cause is an odd species of bacteria, Xylella fastidiosa, that lives in xylem and plugs the xylem vessels, preventing the leaves from getting enough water. The trees decline due to water stress. Xylella moves from one tree to another with the help of little insects called sharpshooters.
In Italy, olive trees are dying and threatening the important olive oil industry. The cause of this disease is the same bacterium, Xylella fastidiosa, carried by sharpshooters. Xylella is probably not native to Europe, but may have been brought there by the international trade in horticulture. Industrial horticulture moves plants all over the world, and some of these carry deadly pests and pathogens. Xylella also causes disease in Brazilian citrus, Georgia peaches and California grapes.
For the full story, see my column at Planet Experts: A Fastidious Disease of Olives, Grapes and Shade Trees