Title: Bacterial leaf scorch distribution and isothermal lines (PROJECT NC-EM-08-02)
Author: Adams, Gerard C.; Catall, Mursel; Walla, James; Gould, Ann B.;
Source: In: Potter, Kevin M.; Conkling, Barbara L., eds. 2013. Forest health monitoring: national status, trends, and analysis 2011. Gen. Tech. Rep. SRS-GTR-185. Asheville, NC: USDA-Forest Service, Southern Research Station. 133-142.
Publication Series: Paper (invited, offered, keynote)
Description: Bacterial leaf scorch (BLS) of shade trees is the common name for a disease caused by Xylella fastidiosa, a xylem-inhabiting bacterium that has fastidious nutritional requirements and is difficult to culture or verify by culturing. Forest trees including oak, sycamore, elm, planetree, sweetgum, mulberry and maple are species susceptible to Xylella infection (McElrone and others 1999) throughout the Eastern and Southeastern United States. It is not yet known how common and widespread BLS is in trees in the North Central States (Iowa, Illinois, Indiana, Michigan, Minnesota, Missouri, and Wisconsin) and Plains States (Kansas, Nebraska, North Dakota, and South Dakota). In New Jersey, BLS was first detected in populations of trees in the red oak group in several western counties 20 years ago and since has spread throughout the State, affecting as many as 44 percent of susceptible oaks in some communities (New Jersey Forest Service 2002). Population increases of X. fastidiosa, production of unidentified toxins (Hayward and Mariano 1997), xanthan-like gums, and biofilms in vessel elements lead to water stress symptoms (Simpson and others 2000), especially chlorosis followed by necrosis of leaf margins and interveinal areas, leaf curling, decreased seed production, delayed budbreak, early autumn dormancy, decline, dieback, and sometimes mortality (Barnard and others 1988, Lashomb and others 2002). Increasing incidence and distribution of BLS combined with drought will increase decline and mortality in susceptible hardwoods. Moisture stress increases the expression of symptoms of BLS. Xylella is vectored by various insects in the Homoptera family including sharpshooter leafhoppers and spittlebugs (Pooler and others 1997). Introduction of new vectors that are more efficient in transmitting the pathogen can increase the economic damage caused by the disease as occurred in California when the glassy-winged sharpshooter increased the incidence of the X. fastidiosa-induced disease, Pierce’s disease, which has been threatening the grape crop. X. fastidiosa occurs in numerous strains which have only recently been well distinguished (Qin and others 2001). One strain causes citrus variegated chlorosis (CVC), a disease infecting citrus trees. Currently in Brazil about 5 million diseased trees are destroyed yearly, causing approximately $50 million in losses. Quarantines are in force in the United States to prevent introduction of the citrus strain. The regional strains of X. fastidiosa in forests and amenity shade trees of the North Central and Plains States do not appear to cause severe disease symptoms like those infecting grape and citrus.
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Adams, Gerard C.; Catall, Mursel; Walla, James; Gould, Ann B. 2013. Bacterial leaf scorch distribution and isothermal lines (PROJECT NC-EM-08-02). In: Potter, Kevin M.; Conkling, Barbara L., eds. 2013. Forest health monitoring: national status, trends, and analysis 2011. Gen. Tech. Rep. SRS-GTR-185. Asheville, NC: USDA-Forest Service, Southern Research Station. 133-142.
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