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Resistant means that American rootstock tolerate phylloxera feeding on them. It does not mean that phylloxera can't or won't feed on them.

As far as I am aware, grape phylloxera only feed on roots from the Vitis genera of plants (grapes). America has multiple species of native grapes, nearly all of which are resistant to phylloxera damage. Since they evolved together, phylloxera and American grapes coexist without too much trouble. The problem started when American grapes were brought to Europe, with phylloxera still on their roots. Vitis vinifera, the wine grape, is the only grape species native to Europe. It had no resistance to phylloxera. Any wine grape infested with it will slowly die. The solution was to graft wine grapes onto American rootstock. This became standard practice in nearly every wine growing region worldwide.

Now I said nearly. There are some wine growing areas that have very sandy soils. Phylloxera prefers clay soils and does not do well in sand. Some of these areas have very limited populations of phylloxera. Washington state in the United States is one example of this. Many vineyards there have self rooted vines. In the few places there that have a phylloxera infestation, the standard practice is to replace any failing vines with grafted vines. Phylloxera spreads very slowly when it's not being transported by humans, so that is not a large number of grape vines annually. Grape vines do also have a production lifespan (production does start to drop off after a few decades), so any areas with more loamy or clay soils in Washington are considering replacing with grafted vines when they do, just to forestall any problems. Areas with sandy soil probably won't bother.

> Grape vines do also have a production lifespan (production does start to drop off after a few decades)

Notably, old vines have fewer grapes, but the quality is higher. Young grapes actually need to have a lot of the fruit removed so that the plant puts more energy (sugar and flavour) into the remaining fruit. As it gets older, you do less of that and the plant keeps putting all that energy into a few grapes.

There are centuries-old vines still being used to produce grapes, but the quantity is tiny relative to even a 50 year old plant, which would be considered quite old.

That is totally correct, but the vineyard's business model will determine whether they are going for high quality or quantity. Some will have multiple labels so that they can cater to different price points.

As everything in the wine world, yes and no.

There are some grape varieties that get significantly better with vine age: Mourvèdre, Zinfandel, Carignan, Grenache.

There are also some grape varieties that don’t do well with vine age: chardonnay, Pinot noir, riesling.

Sure, you’ll see Vielle Vigne on some stuff from Burgundy, but that is for 30-50 year old vines at best. That’s barely adolescent passes for Grenache or Zin.

Also worth noting that Australia has the oldest Syrah and Grenache vines in the world, as our crops weren't affected by phylloxera. Another reason we're strict on border entries.

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