PHYLLOXERA vastatrix (aka Daktulosphaira vitifoliae) is a yellow-colored species of root louse indigenous to the Mississippi River Valley. Phylloxera feeds on vine roots and leaves, causing them to rot and the plant to die, driving the pests in search of new live hosts and spreading inexorably through entire vineyards and regions.
Similar to aphids in appearance, adults are very small, averaging less than 1/25th of an inch in length and range in color from pale yellowish green through shades of orange and brown. Native American varieties developed resistance by evolving a thick and tough root bark, so that they became relatively immune to damage.
Hardly visible, viticulture was long oblivious to phylloxera's destructive potential. Although 17th and 18th Century attempts to propogate V. vinifera vines in Eastern North America failed, the cause was thought to be some kind of poison in the soils.
Outside North America, the effects of phylloxera were entirely unknown until 1863, when species of native American grapevines were taken to botanical gardens in horticulture-crazed Victorian England. Unlike their American cousins, the Euopean vinifera vines had not evolved any resistance or protection, so the stow-away phylloxera began a 30-year rampage through the vineyards of Europe.
Spread through the soil, and on dirt-covered farm equipment, vehicles, tools, boots, grapevine material, soil, and in must and juice, infestations typically reduce crop by 20% in the first year and may render an entire vineyard unprofitable in only 3 years. Sandy soils will slow, but not stop, phylloxera progress. Clay soils that dry and crack to create pathways are the favorite media for its crawling form.
By 1865, phylloxera had spread to vines in the Rhône Valley. Over the next three decades, it inhabited and devastated nearly 70% of the vineyards of Europe. Many methods were attempted to eradicate phylloxera: flooding, where possible, and injecting the soil with carbon bisulfide, had some success in checking the louse, but were costly and the pests came back as soon as the treatments stopped.
American entomologist Charles Valentine Riley realized that the native American vines were resistant and suggested grafting European fruiting wood onto American rootstocks. So, there began a long, laborious process of grafting every wine vine in the infested areas of Europe. It was only in this manner that the European wine industry could be retrieved from extinction. The grateful French government awarded Riley the Cross of the Legion of Honor.
One tragic consequence of this chapter in wine history is the extinction of many of vine species indigenous to Europe. Since they were localized and had negligible commercial value, hundreds were not rescued. Other distinctive and more widely-appealing, but less productive vinifera species also declined.
Some debate ensued, generated by this massive replanting, that the quality of "post-phylloxera" wines was inferior. Whether this was indeed the case and whether this was due to the rootstocks themselves or to the relatively sudden and nearly universal youth of the vines, or to some other concurrent factor or combination of factors makes for lively conversation between wine enthusiasts, but the truth is unknown and may never be conclusively proven.
Phylloxera has continued to spread, infesting the majority of all grape growing areas of the world. California Even the wine districts of Argentina and Chile, once thought to be phylloxera-free are beginning to show signs of infestation.