About one year ago, (WOMC Newsletter, June 1991), we wrote about the deadly root-burrowing louse, phylloxera vastatrix. We included the article as a history lesson. During the latter half of the 19th century, the parasite, which is of American origin, devastated millions of acres of vineyards around the globe. It was brought under control by the French. They saved the day by discovering that they could successfully graft European grapevine varieties onto phylloxera-resistant American rootstocks.
Further research and crossbreeding at the various viticultural schools, institutes and universities, led to the development of “better” rootstocks. These are widely in use today.
Now the media is chirping with alarming reports of a re-infestation of phylloxera in Napa and Sonoma Counties. How did this situation come about, just how serious is it, and can modern technology handle it to termination?
Some say that the bug is new, a mutant, Phylloxera B. Others claim that this is the same insect as before, and offer two possible reasons for its re-emergence. One is that the widely-planted AXR-1 rootstock, introduced by UC Davis as phylloxera-resistant, is, in fact, susceptible. The other explanation points to the unusual weather pattern of the past six years.
Four successive years of drought stressed the vines severely, reducing their vigor to a state of vulnerability. The two years of flooding which followed moved a tons of soil around. This soil contained phylloxera, which then through generations spread like wildfire.
One thing is for certain. The bug is not going away, however it arrived.
The only insecticide fatal to phylloxera, Carbofuran, is unfortunately also fatal to hawks. More than just aesthetic, the hawk’s environmental contribution lies in its predatory control of California’s rodent population. In preservation of this noble, endangered bird, the poison’s use is banned in this state. So, the only remaining option is for the winegrowers to replant.
About one-sixth of Napa County’s 28,000 acres of vines are infested. So far, 1,600 acres there have been removed. Another 1,000 are scheduled for removal after the 1992 crush. Replanting costs a staggering $15,000 per acre. But, it cart be done.
It takes two to five years for the insect to kill a vine. It takes five years for new vines to produce competitive quality grapes. By replacing 20% of their vines each year, regardless of infestation, in ten years growers will have vineyards producing from exclusively healthy vines. By experimenting with new rootstocks as they replant, they may just find the right one, completely resistant to phylloxera.