2019 ASHS Annual Conference

Soil-borne fungal pathogens, such as Verticillium dahliae Kleb., can devastate a wide range of annual and perennial crops. Sustainable management of pathogens is important for profitability and reducing the use of harmful chemicals. Organic soil amendments play an important role in supplying the nutritional needs of vegetable crops while contributing to disease control. The objective of this research was to determine the effects of grape and olive-pomace-based composts on soil-borne pathogen incidence. Field experiments were conducted in both organic and conventional systems during the summer growing season of 2018 on the Cal Poly, San Luis Obispo campus farm. Four different organic amendment treatments were tested including: olive-pomace-based compost, grape-pomace-based compost, dairy manure compost, and plant waste compost. Abundance of the fungal pathogen V. dahliae was assessed from soil samples collected every 6 weeks from May to November 2018. Olive, grape, and plant waste composts showed significant suppression of V. dahliae abundance at two weeks and 8 weeks post application when compared to the control (p ≤ 0.0008). Insufficient evidence correlates farm management type with V. dahliae abundance after adjusting for treatment and time (p = 0.1175).