Green Management of Pierce’s Disease
Ξ February 11th, 2008 | → 0 Comments | ∇ A Day at a Time, Technology |
The history of Pierce’s Disease (PD) in California is punctuated by lulls in its incidence and alternating narratives of successful management and on-the-ground setbacks. Though in the state of California for over one hundred years, the early 1990’s witnessed, beginning in Ventura County, the arrival (from Florida or Texas) of a new insect vector for the pathogen bacterium Xylella fastidiosa responsible for PD: the glassy winged sharpshooter (GWSS). Able to move faster and fly further than native sharpshooter species, though modest evolutionary gains, they proved decisive. The GWSS is now found in the counties of San Diego, Orange, Riverside, San Bernardino, Los Angeles, Santa Barbara, Kern, Tulare, Fresno, and Sacramento. And virtually the balance of the state is threatened.
Yet, as recently as ten years ago optimism ran high in southern California. In 1997, in the Temecula AVA, established in 1984 by the TTB, relief was briefly found in an arsenal of insecticides, specifically Admire. The GWSS seemed to be on the run. Yet Admire and the chemically related Provado, both produced by Bayer AG under the collective name Imidacloprid, proved a very limited solution. By 2000 the vineyards of the Temecula AVA in Riverside county had been devastated. Vine acreage lost between 1999 and 2000 alone was 17%, acreage of white grapes, 22%, owing in particular to Chardonnay’s vulnerability, this in addition to what had already been pulled up.
And pesticides used against GWSS have remained of marginal value to this day, dealing only temporary blows against a tireless, advancing adversary. Further, the pesticides recommended by UC, Riverside, the institution at the forefront of GWSS research in California, all have, no surprise, well-documented environmental risks. Imidacloprid, for example, has been associated with a high incidence of bee mortality. Dimethoate, Cyfluthrin, and Fenpropathrin, each has unintended consequences of varying levels of toxicity, on aquatic life and beneficial insect populations, for example. But unless a grape producer is willing to witness the rapid destruction of their hard work and livelihood, GWSS pesticides remain a front-line necessity, especially for the larger producers. Yet, the financial costs that follow upon a pesticide regime, everything, from the machinery for effective spraying, to the chemical expenses themselves; from storage, field monitoring, EPA reports, to public relations, costs can be staggering, finally shuttering the smaller producer anyway. Everything costs money, subtracting not only from the environment but from the bottom line. All this for the most pastoral, ‘natural’ of libations! However, this unhealthy, unwinnable standoff may be about to change. And UC, Riverside is, again, leading the charge.
New research into sustaining viable vineyard populations of the parasitic wasp, Gonatocerus ashmeadi, a natural predator of the GWSS, through the planting of a variety of floral food resources among the vines, is well underway. Spearheaded by Entomologist Mark Hoddle from UC Riverside, he has already published promising results. And in another more recent study, funded by Western Region of Sustainable Agriculture Research and Education (Western SARE), and also out of UC, Riverside, a study titled Nectar Cover Cropping for Sustainable Pest Management, it offers a fresh look, in part, at plantings of buckwheat in the vineyard for sustaining viable wasp populations, and is currently moving forward. In field trials this year, researchers will examine the success, over the next two years, of cover cropping two organic vineyards, the Bella Vista Winery in the Temecula Valley and a table grape property in Coachella Valley owned by Sun World, with the inexpensive and nectar-rich Buckwheat for the wasp, but also the cahaba vetch, to explore its ability to suppress damaging nematode populations.
A fundamental feature of the project will be to measure the rate of adoption of these techniques by growers. In the project’s words, “The percentage of Temecula, Lodi and Coachella Valley growers that practice nectar cover cropping for pest management will be evaluated at the beginning of the trial (July 2007), and again in June 2010 to determine rate of adoption. The survey will obtain data on whether buckwheat or cahaba vetch cover crops were sown for pest control, and the percentage reduction in pesticide use as reduced as a result of using these management techniques.” In other words, will the grape industry follow? If they do, a function of the project’s success, we may yet move toward a greener vineyard, at least with respect to southern California’s struggle against this awful scourge, the glassy winged sharpshooter.
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