The fragile nature of viticulture – European grapevine moth
There are many diseases and pests that threaten the vine including bacteria such as xylella fastidiosa which kills vines, or viruses such as leafroll or fanleaf which lower yields, delay ripening and reduce longevity of vines. Viruses are usually avoided by using plant materials which have been ‘sanitized’ or by eliminating the vectors which spread them, but the fact is, many winegrowers live with virused vines. Grapevine pests are a great economic threat because they damage the crop itself. Pests include deer, boar, birds and insects like moths. They not only eat the fruit, but damage fruit, which facilitates the rapid spread of fungus.
The introduction of the european grapevine moth in the Oakville district of Napa Valley last September is an ominous reminder of how fast certain pests and diseases can spread. Until that time, the EGVM was found primarily in Europe, and in 2008 introduced into Chile. Since the destruction of that single vineyard’s crop in September, about 50,000 EGVM have been found in vineyards throughout the Napa Valley itself, with four additional counties of Solano, Sonoma, Mendocino and even Fresno in the Central Valley having trapped the pest and taking aggressive action to eradicate it.
At the Anderson Valley (Mendocino) Pinot NoirFestival Technical Conference on May 14th, Mendocino Agricultural Commissioner Anthony Linegar said he would have had a presentation prepared except that it would have been outdated by the time he gave it. Chilling. On April 26th, a winery in North Ukiah found the EVGM in the vineyards. A five-mile radius quarantine was immediately put into effect and pheramone traps set at the rate of 25 traps/square mile. [The traps use hormones to lure males to it and away from females.] Linegar said that when you have 10 moths of the same species in a trap, you know you have a problem. At the time of the meeting, things looked good, but his message was that of vigilence and communication of how the EVGM can be easily transported in order to prevent its spread.
According to Linegar, the EVGM could have arrived in Mendocino County on fruit hauled in from Napa, or on equipment, or in compost. He said it was difficult to detect the pest from checking the cluster because larvae burrow in berries to eat the pulp. Webbing could be a clue of its presence. Compost can be certified by the Integrated Waste Management Board by heating it to 130 degrees for 15 days with multiple daily turns. As to how the EVGM originally arrived in Napa, Linegar said there were some rumors that perhaps it travelled on a piece of European equipment but that most likely, it originated as a “suitcase” cutting. There is a serious investigation going on to determine culpability, with strong enforcement actions to follow.
The EGVM typically has three generations a year. In other countries the EGVM is a continuous problem, growers focus on the 2nd generation to treat. The first generation eats flower clusters, but the vine usually compensates. In the third generation arriving around veraison, it is too late to spray with chemicals. In Mendocino, given its recent introduction, Linegar said they were in eradication stage, going after the first generation. In addition to pheramone traps and conventional treatments, Linegar mentioned organic microbial insecticides such as bacillus thuringiensis and spinosad.
While things looked under control for now and that Mendocino benefits somewhat from its isolation, Linegar said he had the authority to refuse fruit from Napa and that the community of winemakers, growers, haulers and nurseries needed to work together to prevent the spread of this real threat.