Two common vine viruses growers encounter in the vineyard, discussing causes and management options for each.
[Information based on DipWSET D1 material]
1. Fanleaf Virus
What it is: A group of diseases that results in stunted young shoots, distorted cane development, and pale, malformed leaves that look like—you guessed it—a fan. There’s a large range of effects from basically nothing to losing a high percentage of crop. Cabernet Sauvignon is supposedly quite vulnerable. There is no cure—infected plants will eventually have to be removed completely.
How it spreads: Originally, it was spread by the move to grafted vines following phylloxera and the “inadvertent use” of infected plant material. Oops. Nowadays, the disease is spread by the dagger nematode. Bad news: Once nematodes infest your vineyard, they can only be managed, not eliminated.
Prevention
Since there is no cure, the best bet is prevention via soils testing before planting (to check for those bugger nematodes) as well as obtaining virus-tested, clean planting material.
2. Leafroll Virus
What it is: Another group of diseases, this one slows down the growth of roots and shoots as well as grapes—the survivors will take several extra weeks to ripen and will be all kinds of imbalanced with super high acidity, less color, and low sugar levels. It’s noted that the vine itself is unable to store adequate levels of carbs (ie energy), so stunted growth and low sugar totally makes sense.
You know you have the LV when the leaf starts to roll downward in the autumn season and the leaves will also change color similarly to having the Yellows (ie, yellow for white varieties, red for black varieties).
Good news is that having the LV doesn’t not equate to vine death, but does result in reduction of yield by up to half and, as mentioned above, significantly reduced grape quality.
How it spreads: Like Fanleaf, LV was originally spread via grafting. Nowadays, it’s the mealy bug who acts as a vector. Again, like the Fanleaf, symptoms are not always super clear, so you’ve got to get your vines—and rootstocks—tested. It’s noted that some rootstocks may carry the virus without any visible symptoms. (Sound familiar?)
Management:
- Vector control: Mealy bugs like humid environments, so keep an open canopy to deter the buggers. Unfortunately, they’re kind of immune to sprays because they’ve got a kind of waxy exterior. BUT great news: their natural predator is the ladybug—so spread that love around.
- Nursery protocol: Nurseries can/should screen vines for virus infections.
- Vine removal: This is another virus that has no cure. So, unfortunately, infected plants should eventually be removed. Sorry.
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