Organic strawberry production in California is growing. A total of 1,279 acres of organic strawberries, which is almost a ten-fold increase from the 134 acres of 1997, were planted in 2002 with a total farm gate value of 12.5 million dollars (Klonsky, 2003). Virtually nothing is known about factors limiting yield in organic strawberry fields. Most of the research on strawberry production has been conducted in conventional production systems and may not be applicable to organic productions systems. Though choice of variety is very important for success, a study to determine how different strawberry cultivars perform in organic production fields is non-existent and farmers are left to extrapolate from conventional systems. High yield cultivars that are currently used for commercial strawberry production have been evaluated and selected for their yield and fruit quality in conventional agricultural systems (Larson and Shaw, 1995). In organic fields, plants are presented environments that are very different from those in which they were selected.
Dr. Carolee T. Bull, Research Plant Pathologist, USDA/ARS, and her collaborators initiated a project entitled “Evaluation of Cultivars for Yield in Organic Strawberry Production in the Presence or Absence of Mycorrhizal Inoculum” in 1999, receiving partial funding from the California Department of Pesticide Regulation (DPR) and University of California Sustainable Agriculture Research and Education Program (UCSAREP). This was the first evaluation of strawberry cultivar performance under organic management conditions. The overall goal is to provide farmers with research conducted in an explicitly organic setting so that they can make informed choices about cultivar selection, microbial treatments, and disease management issues.
They conducted the cultivar evaluations and experiments with mycorrhizae during the 1999-2000 strawberry-growing season at four certified organic farms in Monterey, Santa Cruz and San Benito Counties. In summary:
• The cultivars Aromas, Pacific, and Seascape were consistently the top performing of those tested. Cultivars Diamante, Douglas, Hecker, Pajaro, Selva, Sequoia, Capitola, Camarosa, Carlsbad, Cartuno, Irvine, and Gaviota were also evaluated. The data indicated that significant differences in yield occur among cultivars grown under organically managed conditions.
• A commercially available mycorrhizal inoculant provided no benefit to organic strawberry production. Although transplants were initially sparsely colonized, inoculation with a commercial inoculant did not increase the percent of the roots colonized when plants were grown in organic fields. Likewise there was no increase in yield due to the mycorrhizal inoculant. The failure may be due to the presence of adequate mycorrhizal inoculum in the organic production fields or high nutrient levels.
• In these evaluations lethal plant diseases such as Verticillium wilt did not limit organic strawberry production in these fields. Other yield limiting diseases were not detected in high levels at any of the locations or on any of the cultivars.