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76 W i n e s & V i n e s s e p t e m b e r 2 0 1 4 Grapegrowing T he southeastern region of the United States is a challenging place to grow wine grapes. The Deep South is prone to spring frosts, stays hot and humid in the summer and is home to many types of mildews and other diseases. In places like Texas the climate may be drier, but it's still very hot in the summer. Rick Naber, owner of Flat Creek Estate Winery, noted that wine grapes in Texas experience an early bud break (often by March 1) and have a threat of frost until late March or early April, after which they suffer high temperatures in the summer and are subject to every disease a grapevine can get. Native grapes are adapted to this climate but make a very different style of wine. One disease that has been killing wine grapes such as vinifera since settlers first brought those grapes to the southeast re- gion is Pierce's disease (PD). Dr. Newton B. Pierce first identified PD in Mission grapes in Southern California in the late 19th century, when the disease damaged thousands of acres around Anaheim, and was then called Anaheim disease. PD is caused by a bacterium, Xylella fastidiosa, which is native to the Gulf Coast region. Vines native to the Gulf Coast ap- pear to be tolerant of this bacteria, and other indigenous plants serve as hosts to the bacteria while not exhibiting any symp- toms of disease themselves. In order for a grapevine to be infected by PD, it must be a susceptible variety and there must be an insect vector present to transmit the bacteria from a host plant to the susceptible vine when the insect feeds on the vine's tissue. Once introduced into a vine, the bacteria colonize the xylem (the tissue that conducts water throughout the plant). When the bacteria occlude the xylem, and water cannot move through the plant, the vine may exhibit symptoms often seen under heat or drought stress. After being infected, vines with Pierce's disease usually die within approximately two years. In the 1970s it was thought that PD was confined to regions with mild winter temperatures. However, with the chang- ing climate, the potential range for PD has expanded, and symptoms of PD have been seen in (formerly) colder western areas in Texas, on vines in Virginia and even as far north as Maryland. Potential Pd problem in Missouri? Southeastern Missouri has been on the borderline of the region defined as sus- ceptible to Pierce's disease, but with warmer winters in the past 10 years, growers began to report symptoms that could be attributed to PD. Texas Pierce's disease program outreach coordinator Jim Kamas, assistant professor and extension fruit specialist in the Depart- ment of Horticultural Sciences at Texas A&M, assessed the risk of PD in Arkansas and Missouri in 2006-07. While he found host plants and vectors for PD, he did not find positive symptoms in grapevines at that time. However, in 2013 a vineyard in central Missouri had significant vine death and sent samples of those Norton vines to Dr. Andrew Walker, professor of viticulture and enology at the University of California, Davis, who does research on PD. Walker found high levels of Xylella fastidiosa, and concern mounted in Missouri that growers were about to face a major problem. WineEast Wine East HIGHLIGHTS • this article reviews the threat of pierce's disease, particularly for southern vineyard regions. • scientists in texas, California and missouri explain their latest findings about preventing and detecting the insect-borne vine disease. • new grapevine crosses bred to resist pD may be available for planting in two years. Controlling PD in Texas and Missouri researchers present latest information about Pierce's disease in grapevines By Linda Jones McKee these scorched Merlot clusters are presenting symptoms of Pierce's disease.