Pierce’s Disease, commonly referred as PD, is caused by a bacterium (Xylella fastidiosa) that reproduces in the grapevine xylem and clogs the water conductivity system. This blockage induces heat- and water-stress type symptoms in times when water and nutrient conductivity in vines is greatest, such as late summer or around the time of veraison. The symptoms may only appear on a few shoots in the first few years of infection.

Often, uneven leaf scorching with a red or yellow margin starts from the outer edges of leaves. Another symptom of PD is called ‘matchstick’ and occurs when leaves fall off, but petioles are retained on the shoot, with the tip looking burnt at one end. Also, infected shoots may have irregular formation of lignin, which becomes apparent when shoot tissue remains green near nodes while surrounding tissues become lignified and brown. Clusters can shrivel and drop due to water stress caused by PD.

(Photo credit: Mizuho Nita)

Vines become infected by a number of vector species, including the glassy-winged sharpshooter (Homalodisca vitripennis), broad-headed sharpshooter (Oncometopia orbona), and other sharpshooter leafhopper species. The pathogen, Xylella fastidiosa, is transmitted by the insect feeding on the vine’s green tissue. When springtime infections occur, the pathogen has time to move through the vine toward the trunk and roots, and it’s more likely to become a systemic infection. Late-season infection, on the other hand, may not result in trunk or root infections. The bacterium is sensitive to cold temperatures, and therefore, Pierce’s disease is more common in mild winter grape growing regions.

Causal Agent: Xylella fastidiosa is a gram-negative, rod-shaped bacterium native to North America. Native and wild grapevines are more tolerant of infections, but these non-symptomatic vines can still be a source of inoculum in the vineyard or surrounding areas.

Management: Vector management is important to limit the spread of Pierce’s disease in the vineyard, since there is no chemical treatment that controls X. fastidiosa in grapevines. If possible, eliminate potential habitats for the vector insects. Sweep or yellow sticky card sampling for vectors should begin at budbreak and continue for several weeks to monitor vector populations in the vineyards and neighboring woodlands or crops in order to determine the site-specific risk level and spray timings. Intensive insecticide spray programs can be applied to vineyards and adjacent areas to create an effective buffer against vectors. Check with your local extension agent or crop consultants for available PD management programs.

Another potential approach, especially in the southeastern US, where disease pressure is very high, is the use of disease-tolerant wine grape cultivars, such as Lenoir (Black Spanish), Lomanto (will open a pdf file from Texas A and M University), or newly released cultivars (e.g., Paseante noir – will open a link to UC Davis), which can withstand X. fastidiosa infection.

Links: 
Google Search on Pierce’s disease and Grapevine (will open a new window)
Google Scholar Search on Pierce’s disease and Grapevine (will open a new window)