DAVIS -- A new form of phylloxera -- related to the subterranean insect that cost California's premium winegrape industry more than $1 billion in replanting costs during the last decade -- has appeared in three grape nurseries over the last two years. One of the University of California's experts on the pest says the new type of phylloxera does not pose a major threat to growers who have switched to resistant rootstock.
"Our friend phylloxera is back," Andrew Walker, a UC Davis viticulture and enology professor, told a large crowd of perhaps 500 concerned growers during the recent Napa Valley Viticultural Fair. "I hope we can calm some of the hysteria."
Walker explained in some detail during his presentation at the fair and in a follow-up interview what scientists know about the pest. The new form of phylloxera is a foliar or leaf-feeding pest. Tell-tale galls form on the underside of fresh grape leaves in addition to attacking roots like the typical California strains of the pest. The finds thus far have all been on the leaves of rootstock varieties. To the relief of the grape growing community, however, the pest does not appear to have an affinity for vinifera varieties such as merlot, chardonnay and cabernet sauvignon.
Although cases of the foliar phylloxera have been noted on wild grape plants in Southern California and elsewhere in the Southwest, the foliar form of this pest has only very rarely appeared in California's wine country before and never stayed more than a portion of a season. This form of phylloxera is common on the East Coast and in Europe, where the combination of high humidity with summertime rainfall is thought to be ideal for its survival. "It is possible that nurseries may have brought rootstock in from the East Coast and the foliar phylloxera may have come along," Walker said. "That's all we know at this point about where it came from and how it got here."
The earlier strains of p
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Contact: John Stumbos
jdstumbos@ucdavis.edu
530-754-9554
University of California - Davis
25-Nov-1998