Bacterial leaf scorch Xylella fastidiosa is one of the most hazardous bacteria in the world, threatening more than 300 different plant species, including such economically and commercially important tree species as oaks, maples, willows,, elms, horse chestnuts, fruit trees and berries such as plums, cherries, raspberries, blackberries, cranberries, and blueberries. The bacteria can also damage many common ornamental plants (hydrangeas, ivy, lavender, rosemary, geraniums, etc.). List of host plants.
Xylella fastidiosa was originally confined to Asia and the Americas. In Europe, it was first detected in 2013 in Italy, where over several years it has caused severe losses to olive growers, destroying more than 300 000 ha of olive trees.
Although the warm climate of southern Europe is more suitable for the spread of the bacterium, EFSA has carried out research and found that the bacterium can also establish and spread in northern European countries.
Xylella fastidiosa cannot be controlled by plant protection products. The disease is transmitted by insects that feed on plant sap, such as spittlebugs. The wide range of host plant species contributes to the rapid spread of the disease. The main measure to stop the spread of the bacteria is to apply strict phytosanitary measures - destroying infected trees and surrounding host plants as quickly as possible. Without action, the bacteria can spread like a fire, to a number of important crops, resulting in significant damage not only to agriculture, but also to biodiversity and the environment.
Transmission:
- The main way of transmission of the bacteria is through planting stock (including ornamental potted plants). Therefore, great care should be taken when importing "green souvenirs" from countries where the Xylella fastidiosa is widespread. Care should be taken with the cultivation or storage of plants of unknown origin in greenhouses used for commercial purposes. The bacteria can be spread by hands, tools and packaging materials.
- In open fields, the bacterium spreads very rapidly by vector organisms - insects that feed on plant sap. One such insect species, the meadow spittlebug, is also widely found in Latvia.
Symptoms:
- Bacteria block the vascular tissue. This inhibits the plant's development, causing leaf wilting, crown dieback and death. In the early stages of infection, some of the leaves start to turn brown (usually on the edges of the leaf blade).
- A yellow or red circle forms around the dead part.
- Eventually, the leaves wither and fall off completely, but the leaf stalks remain attached to the branches.
- The infected trunk and branches develop irregularly, with spots appearing in the new green tissue. Unusually shaped trunk and fruit may form.
Symptoms may vary slightly between host plants depending on the strain of Xylella fastidiosa, which is often host-plant specific.
European Commission list of host plant species and genera of the organism for which susceptibility to the organism or one of its subspecies has been established in the territory of the European Union.
More information:
- EFSA video about bacterial leaf scorch
