Phylloxera. Super Bug, or Super Greed?
by Stephen Reiss, Ph.D., C.W.E.

Originally Presented for the
Master of Wine Program 1992

Phylloxera, the aphid that devastated so many of the world's vineyards in the last century, is once again in the news. This time it is predominately a problem in California where extensive use of the rootstock AxR#1 is common. Phylloxera resistant rootstock was the innovation that helped to combat this pest over 100 years ago, so why then has the rootstock system failed? Robert Mondavi, that paragon of winemaking in Napa Valley, is on the record as saying that the current outbreak of phylloxera is due to a new biotype of the insect, and that it could not be foreseen, nor prevented. Just how accurate is this statement? Could the potential lost of millions of dollars have been prevented?

Recent research, published in the Journal of Economic Entomology, does indeed verify the existence of various biotypes of phylloxera as first proposed by Borner in 1914. These biotypes, or more accurately, races, seem to be host based. That is they are specific to a type of rootstock, rather than a geographical location. This same research suggests that rootstocks of Vitis berlandieri origin contain a natural antibiosis factor that reduces the survivability of the phylloxera. AxR#1 and other Vitis rupestris rootstocks only reduce the fecundity and development of the aphid; rather than its survivability. This helps to explain the success of the Vitis berlandieri based SO 4 rootstock in Europe. While further research is called for, especially in the areas of geographically based biotypes, it seems certain that the use of AxR#1 rootstock is ill advised in regions with phylloxera outbreaks.

Considering its moderate resistance to phylloxera, just how did AxR#1 become so common in California? The best known viticultural text published by the University of California, General Viticulture advises that AxR#1 is "the best available phylloxera-resistant rootstock in the interior valleys." It also states that "This is a case where the choice of a stock cannot be based entirely on its resistance to phylloxera." This in spite of it admonition that AxR#1's "resistance to phylloxera is not high," and that "where phylloxera can be very serious, it may do poorly or even fail."

So why does General Viticulture recommend AxR#1? It cites AxR#1's ease of use, and its vigor. In other words, General Viticulture, and by extension, the University of California, Davis, have ignored the danger of phylloxera for the benefits of ease and profit. Carol Meridith of UC Davis recently remarked to me that much of the supposed AxR#1 rootstock that she distributed may have been mismarked. While this adds additional variables and greater confusion to the problem, it also highlights UC Davis' position that the use of AxR#1 stock was not inappropriate.

Further, Robert Mondavi's quip to the French regarding the potential infestation of AxR#1 rootstock, as published by the Wine Spectator, suggest a blatant rejection of the problem.

This attitude of denial regarding the danger of phylloxera in California is echoed by more popular publications such as Western Fruit Grower. While it is true that they advise the removal of AxR#1, they seem to be more concerned with changes in wine tastes from different stocks, and the use of certified virus free stock, then with suggesting any specific replacement for AxR#1.

What are some of the alternatives to using AxR#1? Certainly the SO 4 stock, which is so popular in Europe is one obvious choice. Its main drawback is its low vigor; however it is more productive on the irrigated and fertile sights where AxR#1 is now used. Like AxR#1, SO 4 roots easily and is not difficult to graft. SO 4, as a V. berlandieri stock, is highly resistant to phylloxera.

In California St. George is primarily used on drier soils, where phylloxera is most at home. While there have not been reports of infestation on St. George stock, its V. rupestris parentage suggests vigilance. Should St. George become at risk to phylloxera, then the V. berlandieri stock, R99 would be worth looking into. R99 does similarly well in drier conditions.

Neither SO 4 nor R99, nor for that matter the many other highly phylloxera-resistant stocks have received much testing in California. AxR#1 had been seen as a panacea for phylloxera, until now. Because of the popularity of AxR#1, there were periods of time it was not available, SO 4 was used as a second choice, and those vineyard managers who were disappointed then, are now delighted at their unexpected fortune.

The skies over Napa and Sonoma are commonly filled with the smoke from the burning phylloxera infested vines that have been uprooted. Most of these vineyards are being replanted, at great expense, to SO 4, despite its lack of acceptance. Had the Californians heeded the warnings of their European counterparts, and questioned the advice of the hallowed halls of UC Davis, much of the costs may have been averted.

The East Coast of the United States has its own unique problem with phylloxera. While Vitis vinifera is immune to the leaf eating stage of phylloxera, many French Hybrids are not. Indeed the native Vitis labruscana grapes, such as the Concord, are well known to host phylloxera; however the pest does not interfere with productivity of the Concord vines. Current studies, as published once again in the Journal of Economic Entomology suggests that there is a real danger to the French Hybrids from wind borne alates and crawlers of phylloxera. The insect was shown to have been dispersed by winds as far as 61 meters. Vineyards of V. labruscana and even wild V. riparia vines, adjacent to rows of French Hybrids, pose the risk of infestation. The isolation of the Hybrids would seem to be in order.

Both the leaf, and the root stages of phylloxera may cripple and even kill the Hybrids. Unlike phylloxera found on the roots of V. vinifera, which does not develop the sexual form, the phylloxera found on Hybrids does indeed mature to sexual forms. Not only does this speed up the rate of infestation, but it allows for the possibility of mutation to more aggressive biotypes.

Phylloxera is alive, and unfortunately quite well in many vineyards in the New World. Only the removal and proper replacement of infested roots for V. vinifera, and the isolation of French Hybrids, can hope to check its spread, and minimize its damage. While it is true that all rootstocks have their drawbacks, certainly destruction by phylloxera must be seen as the greatest drawback of all.