When you're looking for that special bottle of wine to sip by candlelight with your Valentine, you might think organic as well as romantic.

Of course here in Davis, we assume that organic produce is good for us. But we also know there's no such thing as a free lunch. Organic farming might be healthier, but we pay for this through crop loss and higher production costs.

Research at UC Davis is now challenging this conventional wisdom. The organic lunch, while not free, might end up being less expensive than we thought, at least the wine portion of the bill. Graduate student, Don Lotter, and his colleagues, Professor Jeffrey Granett and Dr. Amir Omer in the Department of Entomology at UCD, have found that organic farming techniques might actually protect vineyards against one of their worst enemies.

Phylloxera is a bug - a distant cousin of the common aphid - that eats into grapevine roots and eventually kills the plant. Once the pest invades a vineyard, no amount of chemicals can control it. In fact, the only known way of fighting phylloxera is to replace all vines with resistant rootstock from North American rather than European parentage. The trouble with this solution is the vast expense of uprooting and replanting entire vineyards. Furthermore, while phylloxera has established itself around the world, rootstock technology has not.

If only there were a way of slowing down, or even preventing death-by-phylloxera in vineyards that were infested with the bug. This would at least spread out the cost of vineyard replacement over time. The UCD entomologists suggest that organic farming might be one such delaying tactic.

They cite reports from eastern Europe where phylloxera-infested vineyards supposedly recovered after growers added compost and planted low-growing cover crops, meant to enrich the soil when disked under. In California, these two methods, along with limitations on chemicals, are the main requirements for certification as an organic farm.

Scientists reasoned that some aspect of organic techniques might protect vineyards from phylloxera, either by nailing the bug itself, or by tempering the side-effects of its feeding habits. The pest injures a vine's roots, creating holes through which fungi, ever-present in the soil, invade the plant. These fungi cause massive root-rot, which is a major player in phylloxera damage.

Work on other plants has shown that adding compost to soil can suppress the spread of harmful fungi, while increasing the levels of "good" fungi that combat root-rot in various ways. If a similar effect could be shown for grapevines, we might be one step closer to combating the the ravages of phylloxera.

Lotter and his colleagues took their investigation to California's famous wine-growing regions. Over two years, they studied phylloxera-infested vineyards, 3-5 of which were organic, and 4-8 of which were under conventional management.

The scientists compared the two farming practices for various measures such as amounts of organic matter and nitrogen in the soil, presence and extent of root-rot, and levels of phylloxera infestation in the roots.

The primary results were clear: those vineyards managed organically had significantly less root-rot (9%) than did those managed conventionally (30%). Because the pest populations did not differ between the vineyards, it looks as if organic methods somehow alleivate the side-effects of phylloxera feeding.

Researchers are not yet sure how this works. Between the two types of vineyard, there were no striking or consistent differences in soil quality, organic content, or levels fungi, harmful or beneficial.

While the jury's still out on the connections between microbe balance, organic matter, and root-rot, Lotter and his colleagues are considering another explanation for their results. Organic methods might trigger in the vines a sort of immunity to infection known as "induced resistance" . In other plants, such as cucumbers, compost can have this effect. Conversely, the herbicide, Roundup, commonly used in conventional farming, has been shown to suppress induced resistance.

In trying to unravel the details of how organic vineyards fend off disease, researchers at UCD might provide wine-growers with the only known alternative to combating phylloxera besides all-out vineyard replacement.

Whether the answer lies with bad fungi, good fungi, or the internal defense system of the vines themselves, this research has shown that there are benefits to organic farming other than our own health.

I'll drink to that.

© Kelly Stewart

Dept. of Anthropology, University of California, Davis, CA 95616
e-mail: kjstewart@ucdavis.edu

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