​Les Kincaid's



California's vineyards are facing a serious threat. The combination of a plant disease with no cure and a half-inch-long leafhopper called a glassy-winged sharpshooter has wrought millions of dollars of damage in just a few years. 

Pierce's disease has existed for more than 100 years in the state, but until recently there was no carrier as effective in transmitting the bacteria more than a few feet and spreading the bacteria so rapidly. 

The glassy-winged sharpshooter, first found in 1990 in Ventura County, has spread throughout Southern California. The insect is now moving northward. 

Pierce's Disease 
Pierce's disease is caused by a bacterium, Xylella fastidiosa. The bacterium blocks the xylem, the water- and nutrient-conducting vessels of plants. The typical symptom is for leaves on the plant to begin to dry or to scorch. Infected vines can die in as little as one to two years. 

Xylella fastidiosa also causes almond leaf scorch, phony peach disease, alfalfa dwarf, oleander leaf scorch and citrus variegated chlorosis. 

Pierce's disease decimated 40,000 acres of grapes in the Anaheim, California, area in the late 19th century. It was dubbed Anaheim disease, but the name was later changed because of Newton Pierce, who studied the infection. The incurable plant disease has appeared on and off ever since, but its spread was limited. The principal carrier, or vector, was the blue-green sharpshooter, a weak, small insect not able to fly much further than three feet. 

The Glassy-Winged Sharpshooter 
The glassy-winged sharpshooter, Homalodisca coagulata, is native to the southeastern United States. It was first found in California in 1990. It is a large insect, almost a half-inch (12 mm) in length. It is a dark brown to black. Its head and back are stippled with either ivory or yellowish spots. It receives its name from its transparent wings. 

The glassy-winged sharpshooter can fly up to one-quarter of a mile, and it frequently appears in high numbers. The insect is able to survive winter temperatures dipping as low as 20 degrees Fahrenheit. 

The insect overwinters as an adult. It begins laying egg masses from late February through May. The year's first generation matures as adults from May through August. The year's second generation begins as egg masses laid from June through September. It is this generation that produces the next year's offspring. 

How the Glassy-Winged Sharpshooter Spreads Pierce's Disease 
The glassy-winged sharpshooter is a voracious eater. It can consume 10 times its body weight in liquids per hour. 

Sharpshooters can acquire the bacterium from infected plants and transmit it to healthy plants while feeding. If the adult stage of the insect has the bacterium that causes Pierce's disease, the bacterium remains in its mouthparts throughout its life, which can last over 6 months. 

In some host plants, such as grape, the bacteria can spread systemically and cause disease.  Once in the plant, the bacteria multiply and block the xylem, or water-conducting vessels of the plants. Plants eventually develop symptoms of dry or scorched leaves, particularly in mid-summer. 

Once a plant is contaminated with Pierce's disease, the plant can act as a reservoir of the bacterium. Any sharpshooter that feeds on the plant can pass the infection to other plants.  Once an adult sharpshooter acquires the bacterium, it may transmit the disease throughout the rest of its life. 

Glassy Winged Sharpshooter