The newest critter to haunt California grape growers is the European grapevine moth, which is threatening growers to the point that the California Department of Food and Agriculture has quarantined 162 square miles of land, mostly in the heart of the Napa Valley but also in parts of Sonoma and Solano counties. The moth burrows into the grape and turns it to mush. It seems to be especially fond of Cabernet and Merlot, having destroyed nine acres in Napa’s Oakville district last September. In Europe, it prefers white grapes. The moth cocoons on the bark of the vine in the winter and emerges from dormancy in the spring at the same time that the vine does.
Native to Southern Italy, the moth has traveled throughout Europe, North and West Africa, the Middle East, and Eastern Russia. In 2008, it was found in Japan and Chile after growers purchased used harvest equipment. But this is its first appearance in North America.
In the 1990s, phylloxera tortured grape growers by destroying countless vineyard acres throughout California. This sap-sucking root louse fed on grape roots almost everywhere in the state, and vineyards had to be replanted on resistant rootstock at great cost to growers. Native to the eastern part of the U.S, phylloxera did far worse in Europe, destroying more than three-quarters of all European vineyards after it was introduced by English botanists, who collected specimens of American vines in the 1850s. Californians paid an enormous price when they ignored Europe’s experience and failed to plant vineyards on resistant rootstock.
Also native to the southeastern United States, the glassy-winged sharpshooter showed up in California in 1996. Less picky than phylloxera but potentially just as lethal, this leafhopper lays its eggs on the underside of leaves and doesn’t really care which leaves. Grapes, citrus, almond, stone fruit, and oleanders are just a few that will serve its purposes. But it is particularly dangerous to grape vines because it spreads a bacterium that causes deadly Pierce’s Disease. Successful work is currently underway at the University of California at Davis to breed resistance into grapevines. So far, no sightings have been reported in other countries.
Today, science is hugely helpful when these threats occur unlike the 1850s, when distraught French farmers buried a live toad under each ailing vine in phylloxera infested vineyards to draw out the “poison.” Decades later, employing the scientific method, the French eventually learned that they could graft cuttings onto resistant rootstock to eliminate the problem.
No one yet knows how the European moth was introduced to Napa, but county, state, and federal agriculture commissioners have wasted no time in implementing the quarantine. They will be regulating the harvest and handling of grapes and other related fruit, including persimmons, olives, pomegranates, and kiwi. In order to confine the infestation, crops will not be removed from the land. Growers, nurseries, landscapers, and agricultural workers are all contributing to the effort.
In the quarantined area, sticky strips draw moths, mainly so that monitors can evaluate pest numbers. To thwart reproduction, mating disruption dispensers have been installed to emit the female pheromone that attracts males, who will unsuccessfully search for a mate until they die. Growers may use organic pesticides and will bring in predatory wasps and bats. Time is of the essence as the moths emerge from their cocoons now that spring has arrived. But science, agricultural authorities, and grape growers are all cooperatively engaged to confine and control the menace.