By Clint Thompson
Southeast grape producers should be mindful of Pierce’s Disease (PD) potentially developing in their respective vineyards. Sarah Lowder, University of Georgia (UGA) viticulture Extension specialist, highlighted in the UGA Viticulture Blog that the disease is more likely to show up later in the season.
“Generally, the first symptom to show up is marginal necrosis on the leaves. In red varieties, that tends to have more of a red border, but in white varieties it won’t be as red, obviously. Marginal necrosis is the first symptom,” Lowder noted.
Grape growers must be aware that similar symptoms of other issues can occur as well, such as nutrition imbalance, viruses and crown gall. Producers should contact their county Extension agents who can test to determine if Pierce’s Disease is the issue.
“If you suspect PD or just want a second set of eyes on a problem vine, give your county agent a call or shoot them an email. Early identification helps not just your vineyard, but the whole region’s long-term vine health,” Lowder wrote.
Lowder said that symptoms seem to be more prevalent during drought, or prolonged periods of dry weather. That has not been the case this year, however, with North Georgia receiving its share of rainfall.
Pierce’s disease is caused by a bacterium that is transmitted by numerous sharpshooter insects, including the glassy-winged sharpshooter. It clogs the grape xylem, cutting off nutrient and water flow. Once grapes are infected with the disease, vines die within one to two years.
Once infected with Pierce’s disease, vines die within one to two years. Because of Georgia’s warm climate, European grape varieties like merlot and chardonnay can only be grown in the foothills of the north Georgia mountains. Colder temperatures reduce the number of insects present as well as bacterial numbers in the plant.
Lowder said the disease is transmitted by a bunch of different sharpshooters and leaf hoppers. The glassy-winged sharpshooter is the best vector, though they can be more prevalent further south.