Pierce's Disease
Insect Vectors
Pierce's Disease (PD) is caused by the bacterium Xylella fastidiosa (Xf) and is transmitted by insects following feeding on the host. Affected grapevines are mainly on edge rows planted next to a riparian area that are breeding habitats for insect vector populations. The introduction to California of the Glassy-winged sharpshooter (GWSS) changed the disease epidemiology because unlike the other vectors, GWSS moves Xf long distance. Controlling insect populations is key to managing PD.
Disease Symptoms
PD was identified in California since the late 19th century. The disease is now in several viticulture areas worldwide. The disease is caused by the xylem-dwelling bacterium Xf. The host responds to infection by occluding vessels to curtail the pathogen spread which in turns interrupts the transport of water and nutrients. As a result the vine looses vigor and expresses drought-related symptoms including leaf scorching (Figure 1), fruit raisining (Figure 2) and reduced canopy growth (Figure 3). Grapevine can die within a few years contracting the disease.
Other characteristic symptoms include uneven periderm maturation (a.k.a. green island; Figure 4) and leaf abscission with petiole remaining attached to the cane (a.k.a. matchsticks; Figure 5). All Vitis vinifera cultivars commonly planted for wine and table grape production are susceptible to PD. PD resistance has been identified in several American wild grapes and was introgressed into V. vinifera. Today, several PD-resistant grape hybrid varieties are commercially available.