Phylloxera

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iGrape Phylloxera

Image:Dactylosphaera vitifolii 1 meyers 1888 v13 p621.png

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hemiptera
Suborder:	Homoptera
Family:	Phylloxeridae
Genus:	Daktulosphaira
Species:	D. vitifoliae

Binomial name

Daktulosphaira vitifoliae

Grape Phylloxera (Daktulosphaira vitifoliae, family Phylloxeridae, superfamily Aphidoidea) is a pest of commercial grapevines worldwide, originally native to eastern North America. These tiny, pale yellow sap-sucking insects, related to aphids, attack the roots of grape vines. The insects 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.

[edit] Fighting the "Phylloxera plague"

In the late 1800s the Phylloxera epidemic destroyed most of the vineyards for wine grapes in Europe. Phylloxera was inadvertently introduced to Europe in the 1860s, possibly on imported North American vinestocks or plants. Because phylloxera is native to North America, the native grape species there are at least partially resistant. By contrast, the European wine grape Vitis vinifera is very susceptible to the aphid. The epidemic devastated most of the European wine growing industry. In 1863 the first vines began to deteriorate in the southern Rhône region of France. The problem spread rapidly across the continent. In France alone, total wine production fell from 84.5 million hecta-liters in 1875 to only 23.4 million hecta-liters. Some estimates hold that between two-thirds and nine-tenths of all European vineyards were destroyed.

In France, some grape growers were so desperate that they buried a 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 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 varieties have never gained the popularity of the traditional ones, and in the EU are generally banned or at least strongly discouraged from use in quality wine.

Use of a resistant rootstock, promoted by T.V. Munson, involves 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. In California, many growers used a rootstock called AxR1 which was thought to be resistant. Although phylloxera initially did not feed heavily on AxR1 roots, mutation and selective pressures within the phylloxera population eventually broke down its resistance, resulting in the failure of a number of vineyards, and 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. Modern phylloxera infestation also occurs when wineries are in need of fruit immediately and cannot 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. 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.

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.