Grape phylloxera (Daktulosphaira vitifoliae, family Phylloxeridae), commonly just called Phylloxera, is a pest of commercial grapevines worldwide, originally native to eastern North America. These tiny, pale yellow sap-sucking insects, related to aphids, feed on the roots of grapevines. In Vitis vinifera, the resulting deformations ("nodosities" and "tuberosities") and secondary fungal infections can girdle roots, gradually cutting off the flow of nutrients and water to the vine. Nymphs also form protective galls on the undersides of grapevine leaves and overwinter under the bark or on the vine roots; these leaf galls are not found on vines grown in California.
In France, some grape growers were so desperate that they buried a live toad under each vine. Areas with sandy soils were spared, and the spread was slowed in dry climates, but gradually the aphid spread across the continent. A huge amount of research was devoted to finding a solution to the Phylloxera problem, and two major solutions gradually emerged: hybridization and resistant rootstocks.
Hybridization was the breeding of Vitis vinifera with resistant species. Native American grapes Vitis labrusca are naturally Phylloxera resistant but have aromas that are off-putting to palates accustomed to European grapes. The intent of the cross was to generate a hybrid vine that was resistant to Phylloxera but produced wine that did not taste like the native grape. Ironically, the hybrids tend not to be especially resistant to Phylloxera, although they are much more hardy with respect to climate and other vine diseases. The new hybrid varieties have never gained the popularity of the traditional ones. In the EU they are generally banned or at least strongly discouraged from use in quality wine, although they are still in widespread use in much of North America, such as Missouri, Ontario, and upstate New York, where they yield commercially acceptable wines.
Use of a resistant, or tolerant rootstock, developed by Charles Valentine Riley in collaboration with J. E. Planchon and promoted by T. V. Munson, involved grafting a Vitis vinifera scion onto the roots of a resistant Vitis labrusca or other American native species. This is the preferred method today, because the rootstock does not interfere with the development of the wine grapes, and it furthermore allows the customization of the rootstock to soil and weather conditions, as well as desired vigor. Unfortunately not all rootstocks are equally resistant. Between the 1960s and the 1980s in California, many growers used a rootstock called AxR1. Even though it had already failed in many parts of the world by the early twentieth century, it was thought to be resistant by growers in California. Although Phylloxera initially did not feed heavily on AxR1 roots, within twenty years, mutation and selective pressures within the Phylloxera population began to overcome this rootstock, resulting in the eventual failure of most vineyards planted on AxR1. The replanting of afflicted vineyards continues today. Many have suggested that this failure was predictable, as one parent of AxR1 is in fact a susceptible V. vinifera cultivar. But the transmission of Phylloxera tolerance is more complex, as is demonstrated by the continued success of 41B, an F1 hybrid of Vitis berlandieri and Vitis vinifera. The full story of the planting of AxR1 in California, its recommendation, the warnings, financial consequences, and subsequent recriminations remains to be told. Modern Phylloxera infestation also occurs when wineries are in need of fruit immediately, and choose to plant ungrafted vines rather than wait for grafted vines to be available.
The use of resistant American rootstock to guard against Phylloxera also brought about a debate that remains unsettled to this day: whether self-rooted vines produce better wine than those that are grafted. Of course, the argument is essentially irrelevant wherever Phylloxera exists. Had American rootstock not been available and used, there would be no V. vinifera wine industry in Europe or most other places other than Chile, Washington State, and most of Australia. Cyprus avoided the Phylloxera plague, and thus its wine stock has not been grafted for phylloxera resistant purposes.
The only European grape that is natively resistant to Phylloxera is the Assyrtiko grape which grows on the volcanic island of Santorini, Greece, although it is not clear whether the resistance is due to the rootstock itself or the volcanic ash on which it grows.