Compost-Induced Disease Suppressive Soils for Control of Verticillium Wilt of Strawberry

View the project final report

• 2013 annual report
• 2014 annual report
• 2015 annual report

Commodities

• Fruits: berries (strawberries)

Practices

• Crop Production: biological inoculants, municipal wastes, organic fertilizers
• Education and Training: extension, networking, on-farm/ranch research
• Pest Management: biological control, competition, cultural control, integrated pest management
• Production Systems: organic agriculture
• Soil Management: earthworms, organic matter, soil analysis, soil microbiology, soil quality/health
• Sustainable Communities: social networks

California produces more than 80% of fresh strawberries in the United States. Critical to this success has been management of soilborne diseases, especially Verticillium wilt caused by Verticillium dahliae, using pre-plant soil fumigation with Methyl Bromide (MB). However, international regulations require a phase out of MB, likely completed in 2014. Alternative fumigants have been developed, but regulatory pressures may soon render them unavailable. Consequently, non-chemical alternatives for sustainable management of soilborne diseases are urgently needed. Disease suppressive soil is a well-known phenomenon in which soilborne diseases fail to develop in spite of high infestation levels. Qualitative and quantitative changes in the soil microflora are generally regarded as the key suppressive mechanism. Some soils are naturally suppressive; however, suppressiveness can be induced by the addition of soil amendments such as compost. Previous work shows promise for managing Verticillium wilt with compost. Specifically, reduced wilt on several host crops has been effected by compost, microbial antagonists of V. dahliae have been identified in vitro, and strawberry roots have shown preferential colonization by V. dahliae antagonists.  We propose to investigate the use of compost for management of Verticillium wilt in the California Central Coast strawberry-growing region. With three local composting facilities, we will evaluate the suppressive effects of composts in greenhouse and grower-field trials on certified organic land, conventionally managed soils and soilless-substrate systems. Compost and soils will be characterized by microbial and physiochemical properties to identify correlations with suppressiveness.  The industry-wide shift in strawberry production generates a tremendous need for knowledge transfer and grower support. Accordingly, as a complement to the proposed biological research, we will employ social network analysis and grower-identified needs assessment to identify pathways of knowledge transfer among strawberry growers and to better understand grower perceptions of their goals, needs and management styles to best develop MB-alternative outreach.

1. 1. Evaluate locally available composts for suppression of Verticillium wilt caused by Verticillium dahliae.
      1. 1. Test compost in certified organic and conventionally managed field soil greenhouse and field trials

1. 1. Identify factors in compost, physical and/or microbial, that strongly correlate with disease suppression to enhance consistency and reproducibility of compost applications.

1. 1. Improve outreach and extension efficiency.
      1. 1. Use Q-methodology to generate grower-identified needs and priorities.
      1. 1. Conduct a social network analysis to map pathways of knowledge transfer.