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Symptoms of Pierce's Disease has shown up in some Tennessee Vineyards. Thsi disease is being found in areas that had previously been considered to be too cold, probably as a result of several years with mild winters.
Pierce's Disease (PD)is caused by the bacteria, Xyllela fastidiosa. PD is a xylem-limiting disease that inhibits the transport of water and nutrients within the vine causing a decline and eventual death to the vine.
Sharpshooter insects, expecially the glassy-winged sharpshooter, are thought to be the primary vectors responsible for puncturing plant tissue, thus introducing the bacteria into the vine where it can proliferate. Other insects, such as spittlebugs, and grafting using infected material may also infect vines.
Sumptoms of Pierce's Disease include:
- Dead areas on the leaf blade near the margin. With white grapes, a yellow colored zone may separate the dead area from the living portion. This band may be red on black-fruited varieties. While the band generally develops, it is not always present.
- As more of the leaf tissues dies the leaf blade will ddrop, but the petiole will remain attached to the vine. Late in the season, this may bot be aan indicator of PD since other factors may cause the same thing
- Islands of green" on infected canes are patches of green issue surrounded by dark bwobn mature tissue. They will persist into the winter months.
- Grape clusters will shrivel on infected canes.
Often, PD will affect one cane or cordon on a vine while the rest of the vine continues to look normal. The following year, if the plant survives, all growth is apt to be stunted.
Differences exist among types of grapes and varieties of grapes in regard to Pierces's Disease susceptibiity. Muscadines and varieties such as Blanc Du Bois are resistant to PD. V. vinifera and V. labrusca varieties are quite susceptible, some more than others. It appears that Vidal is very susceptible to PD, perhaps even more tso than Chardonnay.
Cold weather is the is the best natural defense a plant has against PD. Other than site selection and resistant varieties, no other highly effective, legal or practical control exists at this time. If PD is identified in a vine early enough in its development, aggressive pruning may keep the bacteria from reaching the root system where it will be fairly well protected from low temperatures.
We are very interested in determining where Pierce's Disease may be showing up in Tennessee. If you think PD might be in your vineyard, please contact your county Extension office or Dr. Dave Lockwood (dlockwood@utk.edu). We would like to get pictures and/or samples to help in monitoring the presence of PD. |
Institute
of Agriculture
