Chapter 20

Managing Vineyard Diseases

Bacterial Pathogens

Pierce's Disease

Pierce’s disease is caused by the xylem-inhibiting bacterium, Xylella fastidiosa and is generally fatal to European (vinifera) grapevines. This bacterium interferes with water flow in the xylem placing the vine under potential water stress. This disease has had heavy impacts on V. vinifera grape production in New Mexico, Arizona, and parts of California.

Symptoms

In severely infected vines, bud break is delayed, and shoot growth is slow and stunted. Pierce’s disease results in yellowing and scorching of the leaves that begin on the outer margins and progresses inward (See Figure 20.15).

Transmission

The bacterium that causes Pierce's disease lives in the water-conducting system of plants (the xylem) and is spread from vine to vine by sap-feeding insects that feed on the xylem. Insect vectors for Pierce's disease are leafhoppers (Cicadellidae, known as sharpshooters) that have acquired the casual bacterium from grapevines or native host plants and subsequently feed on susceptible vines.

Disease Management

Cultural Practices: Management of this disease mostly revolves around management of the leafhopper vectors, and this information can be found under “Leafhoppers” in Chapter 22, Managing Vineyard Insect Pests. Vineyards in close proximity to sharpshooter habitats are most at risk. Growers should monitor these habitats for sharpshooters, using sticky traps to track their movement into vineyards, and apply insecticides accordingly.

Chemicals: There are no effective control measures currently available for Pierce’s disease when infected sharpshooter vectors are present.

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