Pierce's Disease of Texas Grapevines

Abstract

Since 1977, it was believed the grape strain of Xylella fastidiosa, Pierce's Disease (PD), was limited to sites receiving less than 800 hours of winter chilling below 45 °F. Warm winters since 1992–93 resulted in numerous PD-positive vineyards in central Texas which were previously nonaffected. Vine mortality ranges from minimal to over 80% dead vines. A Davis Mountains site receiving over 1,000 hours was also severely infected in 1996. The last severe winter in Texas was 1989–90; therefore, warm winters could be contributing. This climatic change could have affected vines, vectors, bacteria, and/or hosts. Recent work based on a study of 20 PD samples, 11 from Texas and 9 from other states, including California and Florida, indicates that the samples of PD grape strain of Xylella fastidiosa are clonally related. ELISA tests failed to identify PD from 1994–96; therefore, a sensitive REP-PCR test is needed before vine, bacteria, vector, and host management strategies can be developed.