Biofumigation in wine grape vineyards could prove to be a natural, effective, and economical way to rid soils of pests and diseases while eliminating the growing disdain from policymakers over chemical fumigant use including methyl bromide.

Four Napa Valley, Calif., vineyard management companies and wineries are currently testing natural fumigation (biofumigation) in conjunction with holistic practices in 12 to 15-acre Cabernet Sauvignon wine grape vineyards under the guidance of Bob Shaffer, agronomist, Soil Culture Consulting, Glen Ellen, Calif.

The vineyard sites include: Chateau Montelena Estate, Calistoga; Far Niente Nickel and Nickel Estate, Oakville; Piña Vineyard Management's Sawyer Cellars, Rutherford; and Renteria Vineyard Management's Stice Lane Vineyard, St. Helena.

“Lowering pest populations with biofumigation, fallowing, cover crops, specifically amended composts, inoculants at vine transplanting, and balancing minerals increases the health of the soil plus pest resistance and tolerance in the vine,” Shaffer says.

Biofumigation involves planting Brassica genus plants with high levels of glucosinolates which decompose into isothiocyanate to disrupt the life cycles of soilborne pests including plant parasitic nematodes, parasitic fungi, and weed seeds.

In the Napa Valley, the dagger nematode X. index is one such parasite that causes substantial damage to vine roots; not so much for feeding damage and related yield reduction, but for the transmission of the grapevine fan leaf virus.

“We're using a holistic approach before and during the replanting of fields where dagger nematodes are present in wine grape vineyards,” Shaffer says. “The holistic view seeks to elevate the health of the vineyard's ecology, soil, and vines to create functional biochemical factors that favor vine health.”

Rootstocks chosen for the test sites are based on producing high quality wine, not dagger nematode resistance, Shaffer notes.

Here's how biofumigation works: Fallowing a field for one to two years is best — and isn't mandatory, but provides more benefits, Shaffer says.

In a vineyard cleared for replanting, analyses of soil chemical and physical factors are conducted to determine actual soil pests and the mineral balance. If the soil's living microbial biomass weight is low, this means soil humus levels are low. It also indicates that inadequate carbon inputs exist, the mineral balance is off, slower decomposition is occurring, poor structure is present, and high populations of plant parasitic nematodes and parasitic fungi exist.

In the fall, the seed bed is planted with Brassica crops high in glucosinolate. In the spring, Brassicas are green manured 4 to 6 inches deep in the soil. A follow-up irrigation cycle speeds up the Brassica decomposition and aids microbes in the decomposition process. Gases released from the plant material can kill nematodes, weed seeds, and other disease organisms.

Shaffer says vineyard test results are yielding healthier vines and fewer dagger nematodes.

“The holistic farming plan is showing good vine growth, low or no presence of dagger nematodes, and noticeably improved soil structure,” Shaffer says. “Biofumigation is elevating soil health while providing the vine with nutrients for improved pest tolerance and resistance.”

Piña Vineyard Management is in its third year of biofumigation testing. “The results look promising,” says John Derr, Piña viticulturist. “We're still evaluating this method to determine if this is the direction we want to go. I'm convinced that an organic route, not chemicals, is the most logical and environmentally-friendly path to prepare vineyard soils for new plantings.”

Finding a better way to control soil issues is imperative to Piña Vineyard Management which plans to remove and replant 20 percent to 30 percent of its existing vineyards over the next 10 to 15 years. The company manages about 50 vineyards over 750 acres mostly in the Napa Valley, plus two vineyards in Sonoma County. They also develop or redevelop vineyards for about 70 clients.

“We'll never get rid of nematodes in this area. Nematode populations could remain in these soils for a thousand years or longer,” Derr says. “Our goal is to manage nematodes so they don't rise above the economic threshold.”

The nematode is the most numerous multi-cellular animal on the planet with thousands in a handful of dirt. The roundworms feed on plant roots by puncturing and sucking the cell contents with stylet needle-like mouthparts resulting in reduced vigor and yield. The plant parasite lives in soil and within or on plant tissues.

Shaffer emphasizes the biofumigation goal is not to eliminate every plant parasitic nematode in the soil. It's about improving soil health and suppressive factors, generating vine health, and increasing disease tolerance and resistance.

While it's too early to determine the actual costs of biofumigation, Shaffer says costs are equal or less than a year's application of conventional nematicide. Plus, the vineyard soil develops an ecology that lowers costs, improves economic yield, and sustains the vine's quality of production. Biofumigation is free of ties to environmental pollution, he says.

Biofumigation is successfully used in other crops including potatoes.

Shaffer, a lifetime farmer, has spent 30 years working with biological, organic farming systems in temperate and sub-tropical environments. Shaffer is working with Hawaiian farmers who face even greater plant parasitic nematode pressures than those faced in the Napa Valley.

He teaches a cover crop class at Napa Valley College where he's trained more than 100 students since 2002 on the use of cover crops, including the Brassica genus, in biofumigation. “Biofumigation is not a silver bullet,” Shaffer says. “It's part of a holistic approach with many components not standardized to every site.”

The only downside to biofumigation is the high skill level and experience in viticulture on the farmer's end to make biofumigation work, Shaffer explains.

Shaffer owns and operates Kona Keei Farm, a certified organic farm in Honaunau, Hawaii. His consulting practice includes 1,000 acres of grains, legumes, vegetables, fruit trees, spices, nursery crops, herbs, and forbs.