Extending the Biologically Integrated Orchard Systems (BIOS) model to Northern San Joaquin Valley Walnut Orchards

Joseph A. Grant

United States walnut production comes almost entirely from about 210,000 acres (85,000 hectares) of orchards in California’s central Sacramento and San Joaquin Valleys. Northern San Joaquin Valley counties (San Joaquin and Stanislaus) account for 26% of this acreage. California walnuts are marketed domestically and abroad, and have an international reputation for high quality.

Walnut production in California is capital and input intensive. Orchard development costs run around $12,000 to $14,000 per acre ($29,700 to $34,600 per hectare). Annual cash production costs are approximately $1,800 per acre ($4,450 per hectare). Nut production begins the fifth or sixth year after planting. For best production and quality, walnuts require deep well-drained soils and around 3.5 feet (1.1 m) of supplemental irrigation during California’s dry hot summers. Nitrogen fertilizers are applied at 150 to 400 pounds N per acre (168 to 449 kg N/ha) annually. Planting densities range from 65 to 115 trees per acre (161 to 284 trees per hectare). Weed free strips are maintained with herbicides under tree rows. Resident vegetation or (increasingly) a planted cover crop in orchard "middles" is mowed or disked three to six times per season. A smooth vegetation free orchard floor is required for mechanized harvest operations in September through November.

Key pests of walnuts in California include walnut blight disease (Xanthomonas campestris p.v. juglandis), codling moth (Cydia pomonella), walnut and dusky-veined aphids (Chromaphis juglandicola and Callaphis juglandis), navel orangeworm (Amyelois transitella), and web-spinning mites (Tetranychus urticae and Tetranychus pacificus). Few reliable economic treatment thresholds exist. Management of key pests is primarily based on timely application of pesticides. Factors contributing to low adoption of biologically based alternatives include high pest pressure, low damage levels required by the market, lack of effective biological alternatives, poor understanding of crop/pest biology among growers and pest management consultants, and a commission-based agricultural input supply infrastructure.

In 1994 through 1997, the Community Alliance with Family Farmers (CAFF) demonstrated the feasibility of reducing pesticide and fertilizer usage in walnuts while still producing high quality walnuts in its innovative and successful Biologically Integrated Orchard Systems (BIOS) project, conducted in two northern California counties. The BIOS approach combines biologically intensive farming practices and intensive orchard monitoring with a hands-on, farmer-to-farmer educational model.

We are adapting the BIOS model to fit the biological, economic, and infrastructural conditions of the walnut farming industry in the northern San Joaquin Valley. We have completed the first of a three-year project in which ten 10 to 30 acre (4 to 12 ha) BIOS demonstration sites were established in commercial northern San Joaquin Valley walnut orchards. Seven of the ten include paired conventionally managed comparison blocks. The UC Cooperative Extension Farm Advisor in San Joaquin County coordinates the project. CAFF coordinates project outreach activities, with guidance from project growers, consultants and the project coordinator. The project is funded by the UC Sustainable Agriculture Research and Education Program with funds from the State of California and US Environmental Protection Agency.

A project implementation team of growers, consultants and scientists familiar biologically intensive orchard management visited each BIOS orchard and compiled a customized farm plan to guide BIOS implementation. Plans include guidance on selection and management of cover crops; pest and disease development models; pheromone mating disruption, beneficial insect releases, and reduced-risk pesticides for codling moth; cultural and biological control of aphids and mites; leaf tissue analysis and nitrogen budgeting to rationalize use of applied nutrients; and substitution of post-emergence herbicide strip treatments with pre-emergence and non-chemical alternatives.

A project field scout monitors key pests, beneficial insects, and crop development in BIOS and conventional comparison blocks weekly, and reports monitoring results to growers and their pest management consultants. Growers manage their BIOS blocks in consultation with their pest management consultants using their farm plans as guides. Growers are asked to manage conventional blocks in their customary manner.

Monitoring data, in-season and year-end nut evaluations, and grower interviews are used to measure program success in terms of crop yields, quality, and pesticide use reduction. Results to date show that growers have successfully reduced insecticide, miticide, and fertilizer use in BIOS blocks. Nut yields and quality are comparable to conventionally managed blocks.

Outreach to growers and other walnut industry clientele was not emphasized during the first project year. Planned future outreach activities include continued publication of a monthly newsletter, monthly grower meetings and monthly PCA meetings, field workshops on brush chipping, cover crops, codling moth management alternatives, and beneficial insect biology.

Joseph A. Grant
University of California Cooperative Extension
420 S. Wilson Way
Stockton, California 95205
Tel: (209) 468-2085
jagrant@ucdavis.edu

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