COLLEGE STATION — Pierce’s Disease, a bacterial ailment carried by tiny insects, is causing devastating losses to Central Texas vineyards, and scientists are scurrying to stop its spread before the industry is crushed.
“Basically, it has just exploded out there, and we don’t know why,” said Dr. Jerral Johnson, plant pathologist for the Texas Agricultural Extension Service. “It’s spreading far and wide.”
Perhaps 10 percent of the state’s 3,100 acres might be infected at this time, according to Dr. George Ray McEachern, Extension pomologist. Only the 1,200-acre High Plains grape acreage appears to be free of the disease at this point.
“It’s the most serious threat to the Texas wine industry in its 25 years of existence,” said McEachern.
Pierce’s Disease, which is more deadly on wine grape varieties than table grapes, had been found on limited acres in Texas in previous years, but growers always have been able to keep the condition in check.
“We’ve had it all along, but not with a lot of damage,” Johnson said. “We’ve lost a couple of vines here and there in the past, but it has gotten a lot worse now.”
And the problem isn’t just in Texas. California growers are suffering a major bout with the disease this year, too. Scientists are not sure what caused the flare-up. More than one-third of California’s Napa Valley is infected, according to Wine Business magazine. A California task force estimates the loss to be at least $18 million due to low production and replanting costs.
Tiny insects called leafhoppers carry the bacterial disease from one plant to another by injecting fluid into grape leaves. The bacteria enters the plants vascular system and blocks up the veins that normally transport water from the roots to the leaf ends.
First signs of the disease are yellowing leaves, then brown tips and eventually only an “island of green” near the stem of the leaf remains. As the leaves are choked off, the plant fails to produce fruit and eventually the vines die.
Johnson and a team of plant pathologists, entomologists, and county Extension horticulturist Jim Kamas been sampling and monitoring vines. Thus far, the most serious outbreak is in Central Texas.
“One vineyard we’ve sampled produced a ton of grapes per acre last year, but this year made only 100 pounds of grapes across the whole acreage,” Johnson said.
Industry leaders are hoping for a solution to the disease outbreak before a serious dent is made in production. In 1995, the industry had an estimated economic impact of $101.9 million on Texas, according to Lisa Allen of the Texas Wine and Grape Growers Association in Grapevine. She said there are about 165 wine grape producers in the state, and about 1 million gallons of wine were produced by Texas’ 26 bonded wineries last year, according to the Texas Wine Marketing Research Institute at Texas Tech University.
“This (disease) is not a huge factor right now,” Allen said. “Overall, the harvest looks good. But Pierce’s Disease is the No. 1 problem in the state, and we don’t want it to this to become an epidemic.”
Johnson said research into the causes of the outbreak has been put on the fast-track.
“We have to work out some kind of management program within a year, otherwise we’ll have so many vineyards that will have gone out,” Johnson said.
He said researchers will be investigating what other plants might be hosting the leafhoppers before they attack the grape vines. The team has collected wine grape vines, vineyard grasses, pasture grasses and native vines near a vineyard that tested positive for Pierce’s Disease.
Current testing methods, however, only work on the wine grape vines, so screenings for the disease in insects or other plants carrying the disease don’t show positive. Dr. Neal Van Alfen, head of the plant pathology department at Texas A&M University, said new DNA- based detection methods are being developed to find the source of the disease in Texas.
“Until Pierce’s Disease can be identified in the vines, hosts and in the vector, an effective management program will be difficult,” McEachern said.
Once that is discovered, scientists will know how to manage — perhaps by removing or spraying the host plants to disrupt the vector insect’s life cycle, Johnson explained.
“This disease is really giving the industry a licking,” he added. “We have to come up with some way to stop it, and that means a large investment for Texas A&M and the vineyards.”
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