Pierce’s disease (PD) is a bacterial disease of grapes named for Newton Pierce, who described the disease in 1892. The bacterium species is Xylella fastidiosa.
A grape plant is infected when insects, particularly sharpshooter leafhoppers, carrying bacteria bite the plant. Bacteria then take up residence in the vascular tissue of the grape and reproduce, forming large colonies that block the transport of water and nutrients. Symptoms typically first appear in hot, dry weather.
- Scorched leaf margins.
- Leaf drop, leaving stalk behind for a characteristic “matchstick” appearance.
- Patches of immature bark on stems.
- Dieback of cordons, the “arms” of the vine.
- Shriveled grapes.
There is no effective treatment for Pierce’s disease. The outcome depends on the variety. Grape varieties fall into three categories:
- Susceptible: Varieties that will eventually die if infected with Pierce’s disease.
- Tolerant: Varieties that may recover if the winter is cold enough to kill the bacteria.
- Resistant: Varieties that will recover, but may still spread the bacteria to other vines.
Susceptible varieties showing symptoms of Pierce’s disease should be destroyed. Tolerant varieties should also be destroyed if the symptoms appear two years in a row.
Purchasing varieties that resist or tolerate Pierce’s disease is a critical first step. Muscadine grapes naturally resist Pierce’s disease. Other PD-resistant varieties have been developed within the last few years, but they are still in the experimental stages and not yet readily available. Home growers, therefore, still have to rely on tolerant varieties.
Further control of Pierce’s disease consists of eliminating sharpshooter leafhoppers. Besides using pest control methods as necessary, keep the vineyard mowed. Also, locate your vineyard away from woods where the bacteria might be lurking.