The Oregon Department of Agriculture (ODA) has ordered a quarantine restricting shipments of plants susceptible to Xylella fastidiosa for nine counties in the state.
The quarantine is necessary for the ODA to work with the nursery industry to ship plants to other states and other countries, says Gary McAninch, the department’s nursery and Christmas tree program manager.
“We’re asking to ship from counties that don’t have the disease,” said McAninch, noting that ODA labs are busy testing samples from the many hosts of the incurable disease.
Xylella fastidiosa is best known in the U.S. for infecting California winegrapes with Pierce’s disease. About 15 years ago, the Temecula region in Southern California was hit hard by the disease, leading the state to take action. Part of the problem was that in Temecula, the disease was spread by a wide-ranging pest known as Glassy-winged sharpshooter.
“We don’t have glassy-winged sharpshooter up here (in Oregon), so we’re not yet sure how big of an issue it is,” said McAninch of the October find in a pear tree in the Hood River area.
The state’s winegrape growers have not reported finding the disease, he said, but the ODA is busy testing grapevine samples from the state’s nurseries in an attempt to make sure they are clean.
The issue of quarantine looms large in Europe, where it is killing olive trees in Italy, said McAninch. It originally arrived in that country on a coffee plant from South America, he said.
The pathogen is considered native to warmer regions in North America such as the Southeastern U.S. In recent years, X. fastidiosa has been reported in Asia, Europe, and South America.
In October, X. fastidiosa was detected for the first time in Oregon infecting pear trees used to make ‘perry,’ or pear cider. Previously, X. fastidiosa was reported infecting pear only in Taiwan.
Oregon produces a number of seed, fruit, and horticultural crops known to be susceptible to X. fastidiosa. The European Union and other countries prohibit or severely restrict importation of plant materials where X. fastidiosa is known to occur.
Measures to exclude this pathogen from disease-free areas in Oregon are the best control options, said McAninch. Controls may include the removal of host trees and best management practices to limit disease spread within specific areas and prevent spread to non-infested areas.
According to a brochure issued this month by the ODA, about 200 plant species are susceptible to X. fastidiosa. Some of the common hosts are almond, American sycamore, annual bluegrass, apricot, blackberry, blueberry, elm, grape, lucerne, maple, northern red oak, peach, periwinkle, plum, raspberry, red mulberry, ryegrass, and strawberry.
X. fastidiosa causes different symptoms on different hosts. The most common symptom is leaf scorch. The margin or edge of the green leaf suddenly starts to dry, a symptom similar to moisture stress, or damage from wind, salt, air pollutants, toxic metals, or nutrient extremes. Later these leaves die and turn brown.
Symptoms are irregular in shape. In general, a bright yellow or red band appears between the healthy and scorched tissue. As the disease progresses, the whole leaf may shrivel and drop, leaving a bare petiole attached to the plant.
Infected trees are often stunted in height due to shortened internodes and have greener, denser foliage than healthy trees. Symptoms may vary depending on the infected host.
X.fastidiosa can be disseminated locally through mechanical and insect transmission. Using pruning shears on an infected plant and then pruning a healthy plant can transmit the pathogen. The most common dissemination is by xylem-feeding insects, which acquire the bacterium while feeding.
Leafhoppers, sharpshooters, and spittlebugs or froghoppers are common vectors in North America. Potential vectors in Oregon include the blue-green sharpshooter (Graphocephala atropunctata) and common spittlebug (Philaenus spumarius). In addition, infected plant parts such as bulbs, tubers, corms, rhizomes, and seeds can harbor the pathogen and lead to long distance dispersal.
Oregon growers are urged to report plants exhibiting suspicious symptoms to the ODA (1-800-INVADER). State officials are asking growers to please take photos of symptoms and details of the suspect plant’s location and the conditions it’s being grown under. Nurseries may contact their official nursery inspector for assistance.
Samples from suspect plants must be submitted to lab testing for accurate diagnosis. An appropriate sample for diagnostic testing consists of a twig about as thick as a pencil with symptomatic leaves still attached.