Pierce’s Disease (PD) is a severe vascular disease of grapevine caused by the Gram-negative bacterium Xylella fastidiosa. X. fastidiosa has a broad host range and can also cause disease in additional important agricultural crops including citrus, almond, olive, coffee, peach, plum among others. The bacterium is transmitted by a number of xylem feeding insects from the family Cercopidae in the Americas. In California, the introduction of the invasive glassy-winged sharpshooter (Figure 1) altered the epidemiology of PD in the Temecula Valley and increased disease incidence to epidemic proportions in the 1990s. The movement of GWSS remain a major threat to viticulture in Central and Northern parts of the state that include the Napa and Sonoma Valleys. Once bacterium has infected the vines it rapidly spreads systemically and multiplies to high titer causing a loss of hydraulic functions. Affected vines can die as quickly as two years. At the whole plant level, PD symptomology manifests into scorched leaves (Figure 2), irregular periderm development (Figure 3), petiole abscission (Figure 4), raisining of berries (Figure 5), canopy stunting and vine death (Figure 6).
Figure 1: Sharpshooters diagnostic and contact information.
Figure 2: Leaf scorching is typical of PD and shows necrosis at the leaf margin with red coloring in red varieties and yellow coloring in white varieties.
Figure 3: Irregular periderm develoment also known as 'green island', is obvious when shoots become lignified before harvest.
Figure 4: Petiole abscission also known as 'match stick', is obvious before harvest.
Figure 5: Berry raisining greatly reduce fruit marketability and quality.
Figure 6: Vines affected by PD decline rapidly and can die as fast as two years.