Two common bacterial diseases growers encounter in the vineyard, discussing causes and management options for each.
[Information based on DipWSET D1 material]
1. Pierce’s Disease
What it is: A bacterial disease that kills vines quickly. The bacteria lives inside and clogs the sap channels of the vines, which leads to vine shriveling, leaf dropping, and eventual vine death anytime between 1 and 5 years. Chardonnay and Pinot Noir are particularly susceptible.
How it spreads: An insect vector called sharpshooters. (The glassy-wing sharpshooter is the guy bumming out California at the moment.)
- Lab testing: unfortunately there’s no way to chemically control the bacteria and the exact symptoms are unclear, so you must have vines tested and diagnosed.
- Control the vector: Sharpshooters, like the blue-green sharpshooter, like living near riverbanks. So, maybe don’t plant there. Some chemical insecticides can also be used, but if thinking more environmentally friendly, consider introducing a predator bug like wasps—these guys will eat the sharpshooter eggs.
- Quarantine: Stricter quarantine rules for vine movement/transfer has helped prevent disease spread.
- Disease resistant vines: They’re working on it…
2. Grapevine Yellows
What it is: A group of diseases caused by a bacteria. There is no treatment. You know you have the Yellows when you experience delayed budburst, drooping vine posture due to new shoots failing to lignify, and the canopy turning—you guessed it—yellow in white varieties, although the black varieties’ canopies will actually turn red. (Grapevine Reds?). With some strains of the bacteria, the vine will die as the disease progresses. Sad.
If the vine doesn’t die, there will be an extreme loss of yield and resulting fruit will have high acidity and low sugar—so basically, it’s poorly developed and extremely imbalanced. Makes sense with the whole droopy canopy thing.
Interesting factoid: I recently heard a viticulturist say that he actually tests the hardness of the canes as an indication of whether the fruit’s developed and ready for harvest. So, it stands to reason that those two things are linked.
Chardonnay and Riesling are noted as being amongst the most susceptible varieties.
How it spreads: Like PD, the Yellows are spread by vectors, most notably the leafhopper, as well as nurseries selling diseased and untreated stock (so, maybe don’t shop there…). Careful: the bacteria can live in other plants as well, including cover crops.
- Control the vector: Leafhoppers can be reduced via insecticides. If you have leafhoppers in your cover crops…pull them out.
- Nursery protocol: Bathe the pruning wood in hot water and kill that disease. (Maybe shop here…)
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