North American Vitis versus Phylloxera
Phylloxera was to the grapevine what the Black Death was to the population of Europe in the fourteenth century. Phylloxera is native to the United States, and no one really knew it was here until Vitis vinifera vines began to be planted in mass quantities.
Phylloxera loves to feed on the root systems of vinifera vines, and soon U.S. vineyards planted with French vines began to die agonizing deaths. North American Vitis grapevines are resistant to the effects of phylloxera. To make matters ten times worse, when American vines were sent to France in the 1860s, phylloxera was sent along with them and proceeded to wipe out most of the vineyards of Europe.
It was an American, T. V. Munson of Texas, who in the 1870s solved the problem by grafting (connecting) vinifera vines onto American Vitis root-stocks. Amazingly, growers could preserve the characteristics of the vinifera vines they loved so much while eradicating phylloxera at the same time.
Things slowly returned to normal, until a new biotype of phylloxera was discovered in the Napa Valley in 1983. Vines once again began to die, because many of the rootstocks in use were the now-infamous AxR1, a cross between an American Vitis grapevine and a European vinifera grapevine. AxR1 was not strong enough to repel this new biotype, and replanting began again.
The AxR1 rootstocks were replaced with stocks having as their basis Vitis riparia, rupestris, and berlandieri vines, which don't make the best wine on their own, but which now allow more appealing vines to share their bounty with the world.
When the new biotype of phylloxera emerged in the Napa Valley in 1983, more than 16,000 acres of vines in Napa and Sonoma counties were replanted at a cost of $1.2 billion. Much more money was lost as vintners waited for newly planted vineyards to become productive.
Phylloxera's Unexpected Gift
Even though phylloxera was a costly fix in California and the rest of the world, the prospect of replanting thousands of vineyard acres gave growers the chance to step back and determine whether they had been planting vines and using rootstocks best suited to their respective locales. If growers had not been getting the most quality out of their vineyards, they now had the opportunity to try new things.
For example, what if a grower has the perfect climate for red grapes, but his vineyard soil is so deep and fertile that the vinifera vine he wants to plant, say, Merlot, grows so full and dense that leaves block the grapes from the sun and inhibit ripening? The grower could graft Merlot vines onto Vitis riparia rootstocks, which don't penetrate the soil too deeply. The result is that the rootstock keeps the Merlot vine in check by denying it the full extent of the soil's nutrients. This holds the vine back and promotes lower yields and higher quality.
