Pierce's Disease

Pierce’s disease, caused by the bacterium Xylella fastidiosa, is a deadly disease of grapevines. It is spread by certain types of xylem feeding leafhoppers (Cicadellidae) known as sharpshooters. The disease is known to be present from California to Florida and south as far as Central America. Its presence has been known since the 1880’s where in Southern California it destroyed 35,000 acres of vineyards. At that time the disease was known as Anaheim Disease, Mysterious Disease and the California Vine Disease. It was eventually named for N. B. Pierce, who extensively studied the disease.

The bacteria, X. fastidiosa, is limited to the xylem or water conducting vessels of plants. Symptoms begin to develop about mid-summer as the bacteria blocks these vessels and a drying or scorching of the leaves is seen. Leaves become chlorotic along the outer edges or adjacent to the dead tissue. The drying or scorching of the leaf continues for a few days to weeks until the leaf eventually falls, usually leaving the petiole attached to the cane. Petioles gradually die back and fall. Maturing canes that turn tan will have green islands along the infected portions. When new growth occurs on infected canes it can be delayed and is usually stunted. Leaves on stunted shoots can have a yellow mottling between the major veins. Depending on the variety of grape, death of the entire vine usually occurs in 1 to 5 years.

In 1997 a survey was conducted to determine the number of leafhopper species, the size of the populations, and their movements in and around vineyards. Fourteen vineyards, twelve in the Texas Hill Country and two in north central Texas, were visited on a bimonthly basis. At each vineyard sweep nets of 30 ft. transects, at least one on each side of the vineyard, were conducted and the leafhoppers collected. Plant species were also noted along each transect in order to determine the preferred host plant of each leafhopper species. Yellow sticky cards were placed at approximately 100 ft intervals and usually one row in or 4 to 5 vines inside the vineyard along the perimeter. The sticky cards were observed and data collected at each visit to the vineyard. Plant samples were collected from each vineyard and will be tested, using Polymerase Chain Reaction (PCR), by the Phytopathology Lab at Texas A&M University.

From this survey, approximately 52 species of leafhoppers were collected and most identified. Samples of all leafhoppers were sent to the USDA ARS Systematic Entomology Laboratory in Beltsville, Maryland for positive identification. Other data collected is presently being analyzed. It is hoped that this survey will provide information as to specifically which leafhoppers are vectors of Pierce’s disease and which plant species play host to these insects.

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