California Wineries Take Major Steps To Improve Vineyards

From protecting grapevines against fungal pathogens to loosening heavy soils and increasing yields, vineyard managers find substantial reasons to use compost and mulch.

Christy Porter

Reprinted by permission from BioCycle Jan 1999 pages 59-62

VINEYARD MANAGERS at world famous wineries in California's Sonoma and Napa Counties are increasingly using compost and mulch in their grape management programs. Their field observations of the benefits of these recycled soil amendments are being verified in university research trials.

Under the guidance of Dr. Jeffrey Granett in the Entomology Department at University of California (UC) Davis, Don Lotter, a Ph.D. candidate, has been monitoring the damage caused by phylloxera in 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," reports Lotter.

His research shows significantly less root rot (11.8 percent) in organically managed phylloxerated vineyards than on phylloxerated roots from conventionally managed vineyards (27.1 percent). 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 vineyards receiving compost applications, Lotter found a trend towards higher populations of beneficial microorganisms that are antagonists to Fusurium. These beneficial microbes include Trichoderma and Pseudontonas or Pseudomanad bacteria.

Lotter's findings add to the increasing pool of research showing the disease suppressive properties of compost. And as restrictions on agricultural chemicals increase, growers continue to look for natural alternatives to pesticides and fungicides. Even some of the chemical controls, like sulfur dust, approved for use in organic vineyards, can pose health problems for workers. "With grapes, the workers have a lot of contact with the canopy as they pull leaves, etc." explains Glenn McGourty, UC Cooperative Extension Advisor. "The sulfur can really irritate the eyes and respiratory tract in certain individuals."

Conventional grape growers typically spend about $40 to $50 per acre for pest and disease suppression. This amount can double in a bad year. While many growers try to compare the costs of compost versus fertilizer or pesticides, it is a difficult comparison because of the multiple benefits of compost. For example, compost may help suppress disease, increase water-holding capacity, add nutrients, etc. Further complicating the equation is the fact that it may take applications over several years to see significant improvements in these areas. A more accurate cost comparison would consider the net return above total operating costs of a conventional farm versus a sustainable or organic farm using compost. And as organic wine is gaining ground in retail sales, organic growers may earn higher prices.

Soil type also has to be factored into the equation. For example, there is 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 grape growing regions of the state such as Napa, Sonoma, Lake, Mendocino, and Monterey counties, as well as the Sacramento Delta and the foothills." Compost is cited as 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 Will Bakx, a soil scientist for Sonoma Compost, which uses urban yard trimmings as a feedstock in material applied to vineyards.

Great Soil Amendment

The price of compost varies according to quantity purchased. The general range is between $6 to $9.50/cubic yard undelivered. Although few California composters offer application services to agricultural crops, Upper Valley Recycling charges $24/ton for compost delivered in the Napa Valley vicinity and an additional $6/ton for application. John White of Pina Vineyard Management is a strong advocate of compost. He has been using it for a number of years and purchases compost 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/acre, White is applying more compost than most vineyard managers. However, the higher application rate may be necessary to help loosen the heavy soils.

Fetzer Vineyards (Hopland, California) 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 a 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 more than 15 years. Although Delicato originally invested in large-scale composting equipment, 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 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's vineyards receive an average of five tons/acre of compost each year over 130 acres. Lab analysis of the corn-post is a standard practice at Delicato. Characteristics tested include nitrogen, phosphorus, and potassium (NPK), other soil nutrients, and heavy metals.

Healthier vines And Increased 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 percent pomace and 30 percent turkey manure with 30 percent 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/acre of compost are applied over the 600 acres of Yount Mill vineyards.

Other vineyards have seen improved vine vigor and yield with compost applications. Bob Pestoni of Upper Valley Recycling (St. Helena, California), producer of Harvest Compost, contracted with Paul Skinner of Vineyard Investigations to study the effect of his compost on vineyard yields. Skinner compared the effects of compost to a control (no applied soil amendments) in Robert Mondavi Winery's Tokolon Z block of Cabernet Sauvignon on St. George rootstock.

After three consecutive years, the study at Mondavi found that blocks with compost applied had increased yields of up to 0.9 tons/acre, while the fruit quality remained the same. Application rates for the study ranged from two to eight tons/acre with the 0.9 tons/acre increase in yield occurring in the eight tons/acre treatment.

Cost of the compost at $24/ton applied at Tokolon was recovered by an increased yield valued at $l,350/ acre. Since the trial ended in 1995, about four tons/acre of compost have been applied annually to 20 acres in Mondavi's Tokolon vineyard.

In addition to annual applications, Skinner also promotes the use of compost to prepare land for new vineyard plantings. "I typically recommend a pre-plant compost application of five to 20 tons/acre, depending on the results of our 'Terroir' soil analysis program," he says. Compost is a good source of trace elements and enhances soil structure."

Pestoni is in a unique position because, in addition to being a compost producer, he owns Rutherford Grove Winery. When asked what application rate he suggests for compost, Pestoni responds: "You have to know your soil. Work with a soil specialist and get a lab analysis. Then we can talk about application rate." Upper Valley Recycling does extensive lab analysis on its Harvest Compost made from grape pomace and rice hulls with lime added - and provides potential customers with the results upon request.

Controlling Weeds, Adding Nutrients

Ben Faber, UC Cooperative Extension advisor in Ventura County has been conducting a demonstration study to examine the effectiveness of mulch and cover crops for erosion control in lemon orchards. "Preliminary results indicate that both the mulch and the cover crops are effective for weed suppression and erosion control," reports Faber. As vineyards continue to expand into hillsides, mulch is a feasible tool for erosion control. Vineyard managers may want to experiment with a minimum mulch depth of three inches; if applied at a six inch depth, the material will likely last for at least two seasons.

Clyde Elmore, a UC Cooperative Extension weed advisor, has researched the use of mulch for weed control in vineyard floor management. From his trials, Elmore concludes: "Green waste wood chips give good weed control. The mulch was persistent in the field and should give long-term weed-control benefits. Because it may last for more than one season, the short-term direct cost is not the best way to evaluate this product." However, many perennial weeds such as field bindweed are not controlled well with organic mulches. Depending on the coarseness of the mulch, two to six inches of material are needed to control most annual weeds.

At Pina Vineyard Management, White applies compost for weed control in his vineyards. He is perfecting a vine row applicator with the hopes to suppress weeds with compost application right next to the vines. "We find this is the most effective way of applying the compost," he says. "The chute will deposit the compost right where we want it and gives us a more concentrated application than broadscale spreading."

Vineyard managers typically use equipment designed for applying manure or other soil amendments like limestone and gypsum. "We use a pull-spreader with spinners on the back, standard agricultural equipment, that is calibrated to deliver a specified amount of compost," explains Upper Valley's Pestoni. "The compost may either be broadcast to cover the vineyard floor between vines or directed to the base of the vine with a banding attachment." Because of hillside plantings and decreasing space between vineyard rows, application is sometimes difficult and can affect application costs and methods.

State Regulations

All large-scale producers of compost are subject to corn-posting regulations promulgated by the California Integrated Waste Management Board. Depending on their composting method, producers are required to maintain the compost pile at a temperature of at least 1310F for a specified number of days. In addition, regulated producers must test their end product to ensure that certain heavy metals and pathogens are within acceptable limits. Most producers also obtain product analysis that shows NPK, pH, and other characteristics of interest to growers.

Producers of mulch are not subject to the regulations and thus are not required to put the material through the "time and temperature" process. However, some producers will subject the material to this process for a minimum time to kill pathogens and weed seeds, but not long enough to fully decompose the material.

Nutrient Content

Many producers will make custom blend products upon request. Norm DeLeuze of ZD Wines in Napa Valley wanted a compost higher in nitrogen than the yard trimmings compost normally produced by his supplier for his vineyard in the Carneros district. Greg Kelly of Napa Garbage Company responded to DeLeuze's needs by adding manure to the feed-stock, increasing nitrogen from 1.59 percent to 2.19 percent and increasing the phosphorus from 0.29 percent to 1.4 percent, producing a more balanced, higher quality compost. DeLeuze was satisfied and Kelly is now selling the new product to other grape growers in the area.

While many vineyard managers use compost to increase organic matter and beneficial organisms, it also contributes nutrients. Yard trimmings or grape pomace compost has a nitrogen content of about 1.5 to two percent translating to about 30 to 40 lbs/ton of nitrogen, which is not immediately bioavailable. According to UC Cooperative Extension Advisor Glenn McGourty, "Grape growers typically apply about 30 lbs/acre of (chemical) nitrogen, and it's cheap at about $18/acre." Although McGourty promotes the use of compost, he points out that compost also has its drawbacks. "Compost is not as predictable as chemicals. That's why agriculture started using chemicals in the first place."

The amount of bioavailable nitrogen in compost is often an uncertainty. Nitrogen is only available to plants in an inorganic form, and most of the nitrogen in compost is initially bound in an organic form. Because the organic nitrogen is slowly "mineralized" into a useable inorganic form over time, compost supplies a slow, time-released dose of nitrogen. Comments one UC Cooperative Extension Advisor: "This slow release of nutrients is ideal for the relatively low nitrogen demands of grapes."

Based in Sacramento, California, Christy Porter promotes use of compost and mulch in agriculture for the California Integrated Waste Management Board. She specializes in the area of compost use in vineyards.

BioCycle Jan 1999 pages 59-62