Best Management Practices
Selecting Sites to Minimize the Risk of Pierce's Disease in Texas
In order to successfully manage Pierce's disease in Texas vineyards, growers need to understand the pathogen and how it behaves in nature and in an infected vineyard.
Although Xylella fastidiosa has been killing susceptible grapevines for hundreds of years, it was first diagnosed in the late 19th century. Pierce's disease was named for Dr. M.B. Pierce who first discovered the disease in plantings of Mission grapevines in southern California. First known as Anaheim disease, the disease was first seen in 1883 in the 10,000 acres of wine, table and raisin grapes near Anaheim California. According to some historical sources, in 1885, two years after the first noted infections, half the acreage in the Anaheim area was dead. On the other side of the country, researchers were working with a similar disease which killed peach trees that is now known as peach phony disease.
In addition to infecting peach and grape, other strains of Xylella fastidiosa are known to cause disease in citrus, alfalfa, oleander, plum and numerous deciduous and evergreen annual and perennial plants. It can generally be thought of as a new world disease of old world crops. Xylella fastidiosa is native to the Gulf Coast of the United States where it resides benignly in many native plants.
The bacterium colonizes the xylem or water conductive tissue of susceptible plants. It disrupts the movement of water by directly occluding the xylem through the congregation of bacterial cells, it causes the production of a substance known as fastidian gum, and by triggering the enlargement of naturally occurring cells known as tyloses. It is also speculated that a toxin may be produced by the bacterium adding to the typical leaf scorch symptoms associated with Pierce's disease.
The bacterium is known to be susceptible to cold and low temperatures limit its distribution to the north. This map produced by Hopkins and Purcell show its suspected range across the United States.
In Texas, we have known for some time that the disease is much more prevalent and likely in areas closer to the Gulf of Mexico. At one time we speculated that constituted the natural range of insect vectors. The pathogen's susceptibility to cold temperatures roughly confined it to areas with 800 hours of winter chilling. We now believe that both are true. Vector populations and survival of Xylella are both much higher in warmer areas of the state.
That said, the range of Pierce's disease appears to be moving. Pierce's disease is confirmed in several locations along the Red River and in Ft. Davis and Alpine in far west Texas where we once believed winter temperatures would keep the disease from becoming established.
There is no cure for Pierce's disease. There are, however things growers can do to manage its impact on commercial grape growing. Selecting a vineyard site with low disease risk and understanding the components of the disease triangle are ways of avoiding Pierce's disease- Being aware of the pathogen and identifying its supplemental hosts, recognizing and managing insect vectors and conducting sound cultural practices in the vineyard are all necessary in managing risk.