It’s that time of year- going into your kid’s classroom and seeing three-quarters of them with gook coming out of their noses, daily news reports on the flu epidemic, loading up on ibuprofen and Nyquil- virus season. All of the talk about the extra-severe flu season this year had me thinking-hmm, potential blog post- what happens when our plant friends are infected with a virus? I went to the winemaker with this question and he got a strange gleam in his eye, but knowing better now, gave me the highlights on an expansive, yet fascinating subject. And by all means, if there is something you want covered more in-depth, just comment and I’d be happy to get you the answer.
One of the biggest challenges a winegrower must deal with (aside from lack of rain) is the health of the vineyard. Vines, like humans, are susceptible to different viruses that can range in severity. Some are minor (think common cold) causing subtle variations in leaf color and growth and others (think Smallpox virus) that can cause vine death. The intensity of the symptoms depends on multiple factors- availability of water, cultural practices, and the clone and rootstock you have chosen. However, symptoms themselves can make diagnosis difficult- while some symptoms are diagnostic in nature, many can look like each other so the virus causing them is not clear. In many cases, the symptoms may not exhibit themselves for years- like an extremely long incubation period- and so, just because there is an absence of symptoms, this does not mean the grapevines are free of virus.
As of now, there are over 60 different viruses that vines are susceptible to. The most famous, nee’ infamous virus outbreak in recent memory was the Phylloxera infestation of the 90’s that hammered the grape growing industry and resulted in massive re-plantings (a blessing in disguise- future blog post alert!)
Leaf with symptomatic Phylloxera
Phylloxera occurred because of the susceptibility of a particular rootstock designated with the code AXR#1- so don’t pick that a password or anything because it’s unlucky! While viruses like Phylloxera and Nepovirus tell you nothing about about the damage they inflict on the vine, others have more descriptive names telling you exactly what they are up to: Fan Leaf Degeneration, Leaf Roll, Corky Bark, Ruepestris Stem Pitting, and most recently, Red Blotch.
Rupestris Stem Pitting
The bad news is once the vineyard has a virus, there is nothing you can do to get rid of it, short of ripping out all of the infected vines- no taking 2 aspirin, eating some chicken soup and waiting it out. The best way to deal with viruses is to avoid them all together- hey, the best offense is a good defense- just ask the Seahawks. The best way to start is to try to ensure you have clean material when planting a vineyard- something that takes time, patience and a reputable nursery to work with. As with human viruses, you want to keep the virus from spreading. With vines, it’s not about coughing into your elbow, washing your hands and refraining from sneezing in someone’s face, it’s all about the vectors. A vector is the catch-all term for any pest that aids in transmitting viruses from vine to vine. Any wine-growing region will be glad to put you on the alert for the glassy-wing sharp-shooter, a pest responsible for spreading the virus that causes Pierce’s Disease. There are also mealy bugs and root lice- the pest responsible for the spread of Phylloxera.
Glassy wing Sharpshooter Mealy bug Root louse
When pest vector infestation is particularly heavy, fumigation with various nematicides and insecticides may be needed. Knowing where you are planting and using the correct rootstocks is tremendously helpful overall, as well. The good news is although almost all vineyards end up with some sort of virus that will cause vine death in the end, the vines can still be productive for a long time despite the viral infection. We all gotta go sometime, and can’t ask too much more than being able to do what you’re meant to do for as long as possible.
On a happier note, I’m sure you’ve all heard the good news that we finally got some precipitation and have more in the forecast! Now, I’m not saying it was all me, but I did wash my car and the rain started two days later…