The dangerous vine disease (PD for short) was first detected in Southern California in 1880, when 20,000 hectares of vines were destroyed in five years. It is also known as California Vine Disease, Mysterious Disease or Anaham Disease (because it is spread as far as Anaham in California). At this time, the plant pathologist Newton B. Pierce (1856-1916) moved to California. It was named after him because of his contribution to its research. From 1933 to 1940, its greatest distribution was in California's Central Valley, from where it spread throughout the south of the USA, Mexico and Central America. In the USA, the entire southern belt from California in the west to Texas and Florida on the east coast is affected.
At the end of the 1990s, the disease became more prevalent again. US Vice President Al Gore approved emergency aid totalling 36 million dollars at the end of 2000 and declared a state of emergency (agricultural) for California. In 2014, PD caused the Californian wine industry a loss of US$ 104 million. The disease is not yet present in Europe. The cooler climate probably prevents it from spreading northwards. However, if climate change should cause it to do so (which is highly likely), it is mainly Mediterranean regions that are at risk.
Symptoms & effects
The disease is caused by the bacterium Xylella fastidiosa; until 1978 it was thought to be caused by viruses. The bacterium causes the vines' ability to transport water to wither completely within one to three years and leads to complete withering. The vectors are various leafhoppers belonging to the cicada family. The most dangerous species is Homalodisca vitripennis, known by the common name Glassy-Winged Sharpshooter (GWSS). Compared to its conspecifics, this species can fly particularly far and infect many more plants. The first signs are usually slight drying and "burning" of leaf margins. This results in a necrotic leaf margin with a chlorotic, yellowish band in white wine varieties or a reddish band in red wine varieties. The fruits also dry out with the first symptoms. The still small grape berries fall off, leaving only the grape cluster attached. Most infected vines die within a year, only a few sprout again the following year. Young plants are generally more susceptible. The effects are strongly dependent on the weather and variety. The warmer the region, the greater the impact.
Susceptibility & resistance of grape varieties
The species Vitis vinifera, Vitis labrusca and Vitis riparia are particularly susceptible. Of the European varieties, Barbera, Chardonnay and Pinot Noir are particularly at risk. The University of California warned of this in a report as early as 1985, but Chardonnay continued to be promoted. Cabernet Sauvignon, Gray Riesling, Merlot, Napa Gamay, Petite Sirah, Ruby Cabernet, Sauvignon Blanc and Thompson Seedless are considered to be moderately susceptible. Varieties of the species Vitis aestivalis, Vitis arizonica, Vitis berlandieri, Vitis candicans and Vitis rupestris are considered resistant. These include Ambulo Blanc, Blanc Du Bois, Caminante Blanc, Camminare Noir, Champanel, Errante Noir, Favorite, Orlando Seedless, Paseante Noir and Roucaneuf.
Control of Pierce's Disease & Flavescence dorée
Pierce's disease has a European relative, flavescence dorée, which is also transmitted by grasshoppers and causes similar damage in southern France, Italy and Spain. In 2002, researchers at the University of California succeeded in implanting a silkworm gene into the genetic material of grapevines using a simple virus. This modified gene produces the protein "cecropin", which kills the pathogen. Another possibility is the breeding of new resistant grape varieties. The vine species Vitis rotundifolia (2 x 20 = 40) is resistant to this disease. However, it has a different set of chromosomes than the species Vitis vinifera (2 x 19 = 38), which is why crossbreeding is very difficult. However, such crosses have been successful in the meantime. See also a list of all pests and diseases under vine enemies.
Picture left: ©enbiotech s.r.l.
Picture right: By Reyes Garcia III, Link
