After harvest, Will Bakx loads trucks with compost and mulch for delivery to vineyards in Sonoma and Napa counties. Bakx, a soil scientist for Sonoma Compost in Petaluma, CA, produces high-quality compost from urban yard trimmings. Many vineyard managers who apply compost and mulch after harvest are finding these products to be useful components of their vineyard floor management program.

While some vineyard managers purchase these soil amendments, others make their own compost from grape pomace. Either way, compost and mulch are products that result from recycling materials that might otherwise be wasted. As many communities collect yard trimmings at the curb to reduce organic materials going to landfills, these materials are being transformed into valuable soil amendments by producers such as Bakx. Growers and researchers alike are discovering the benefits of these recycled soil amendments.

Beneficial microbes in compost may help reduce phylloxera damage

Under the guidance of phylloxera researcher Dr. Jeffrey Granett in the UC Davis Entomology Department, Ph.D. candidate Don Lotter has been monitoring damage caused by phylloxera in organic vineyards for two years. “Indications are that vineyards using compost are doing well if they’ve been applying compost for at least four or five years,” according to Lotter.

Lotter’s research shows significantly less root rot (11.8%) in organically managed phylloxerated vineyards than on phylloxerated roots from conventionally managed vineyards (27.1%). Each of the six organic and seven conventionally farmed vineyards that were monitored have similar sand/silt/clay ratios. All of the vineyards showing favorable results are using compost in combination with winter cover crops.

Phylloxera feeding on the grape roots make the grapevine vulnerable to infection by fungal pathogens, such as Fusarium. However, in the organically managed vineyards, Lotter found a trend toward higher populations of beneficial microorganisms that are antagonists to Fusarium. These beneficial microbes include Trichoderma and Pseudomonas or Pseudomonad bacteria. (Additional information on UC Davis phylloxera research is available at http://entomology.ucdavis.edu/faculty /granett/phypage.htm.)

Compost has long been known for its wealth of microbial activity. Beneficial microbes flourish during the aerobic composting process, where oxygen is made available to the microbes either by turning the heap, thereby increasing the porosity, or by pumping air through a static pile.

There is also a relationship between phylloxera and soil type. According to the University of California Pest Management Guidelines on Grape Phylloxera, “Phylloxera prefers heavy, clay soils, that are commonly found in the cooler grapegrowing regions of the state such as Napa, Sonoma, Lake, Mendocino, and Monterey counties, as well as the Sacramento Delta and the foothills.” Compost is a good soil amendment for improving soil structure and aeration of these heavy soils.

“Compost is an investment in the long term health of the soil and the plants,” asserts Bakx.

Compost builds soils, prepares ground for cover crops

John White of Pina Vineyard Management is a strong advocate of compost. He has been using compost for a number of years and purchases it from several different Napa Valley producers. “We apply compost before planting or within the first year to improve the heavy valley soils and to build soil organic matter,” says White. At an application rate of 10 tons per acre, White is applying more compost than most vineyard managers. However, the higher application rate may be necessary to help loosen heavy soils.

Fetzer Vineyards (Hopland, CA) is a subject of Lotter’s phylloxera study. However, when asked why he uses compost, vineyard manager Tom Piper doesn’t even mention phylloxera damage control. He cites improved soil structure, the addition of potassium, and beneficial microorganisms. In addition, Fetzer sows the seeds for its annual cover crop onto a bed of recently applied compost with good results. Unlike Pina Vineyards, Fetzer makes its own compost on-site.

“We make about 200 tons of compost every year from our pomace,” explains Piper. “We turn it with a front-end loader, so we didn’t need to invest in any special equipment.” Compost is applied at about one ton per acre to established Fetzer vineyards and two tons per acre for new plantings.

Delicato Winery has been composting grape pomace on-site for more than 15 years. Although Delicato originally invested in large-scale composting equipment, such as a Scarab turner, and sold compost to other growers, the winery now only makes enough for its own use, selling the remaining pomace for animal feed.

“Grape compost makes a great soil amendment,” says Bud Bradley, Delicato’s director of grower relations. “It helps make the soil what I call healthy, improving drainage, and water-holding capacity.” Bradley touts the widely held view that soils high in organic matter are not as attractive to nematodes. Delicato vineyards receive an average of five tons per acre of compost each year over 130 acres. Lab analysis of the compost is a standard practice at Delicato. Characteristics tested include nitrogen, phosphorus, and potassium (NPK), other soil nutrients, and heavy metals.

Compost may contribute to healthier vines and increase yields

Andrew Hoxsey of Yount Mill Vineyards is now in his third year of making compost for his organic vineyard with restricted inputs. After experimenting with commercially produced compost, he decided to try making his own custom blend. He now blends 40% pomace and 30% turkey manure with 30% composted yard trimmings from a local commercial compost producer.

Hoxsey is pleased with his blend and finds that vines that were stressed in 1995 and 1996 now appear healthier. “The primary reason we use compost is to add organic matter and boost microbiological activity,” says Hoxsey. Three to four tons per acre of compost is applied over the 600 acres of Yount Mill vineyards.