Pierce’s disease is caused by the bacterium Xylella fastidiosa. Xylella fastidiosa is primarily transmitted through xylem-feeding insects, including spittle bugs, sharpshooters, cicadas, and tube-building spittlebugs. There is some minor evidence that transmission of the pathogen can occur mechanically (e.g., wounding, pruning, etc.). The risk of mechanical transmission may be higher when pruning practices occur during periods of active vine growth. The bacterium can also be transmitted through use of infected propagation material taken from infected grapevines. The symptoms of Pierce’s disease are perennial and will appear late in the summer when weather conditions are predominately hot and dry or when plants are under drought stress. Scorching, seen as chlorosis and green fading colors, will develop at the edges of leaves, which dry and turn brown. Marginal browning can take on an undulating appearance as it moves toward the veins of the leaf. A yellow to red-brown band may be present between the green and scorched areas of the leaves. Leaf symptoms of Pierce’s disease can look very similar to drought stress symptoms; however, the yellow or red-brown band between green and scorched areas will be absent in vines suffering from drought stress. Some vines will have a "matchstick" symptom where the blades have dropped from the plant but petioles remain attached. Plants will may yield limited fruit production, but the clusters will collapse at veraison, a symptom called raisining. Another symptom may occur on stems, where maturation proceeds irregularly and green "islands" are left after browning of the cane is complete. Options for managing Pierce’s disease include the following: • Insecticide treatments are recommended to reduce sharpshooter populations. For managing these vectors within the vineyard, a monitoring program should be practiced to apply materials effectively in accordance with the appearance of vectors. • Vegetation management can help reduce reservoir hosts for the bacterium. Choosing planting sites that are not in proximity to riparian areas with native trees, shrubs, and woody vines is recommended. • Weed management in and around the vineyard will not only reduce competition for the grapevines but can also reduce potential reservoir hosts and host plants that may be desirable for the insects capable of transmitting X. fastidiosa. • Remove and destroy infected vines as soon as they are identified in the vineyard. • While the risk of transmitting the bacterium during dormant pruning practices is low, it is recommended that pruning equipment be “sanitized” periodically to reduce mechanical transmission. • Avoid propagating infected grapevines. Grape growers should purchase plants from reliable viticulture suppliers.

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