Rotations with Broccoli - A Sustainable Alternative to Soil Chemical Fumigants

Project Overview

Project Type: Research and Education
Funds awarded in 1999: $145,750.00
Projected End Date: 12/31/2001
Region: Western
State: California
Principal Investigator:
Krishna Subbarao
University of California, Davis

Information Products


  • Fruits: berries (strawberries)
  • Vegetables: broccoli, brussel sprouts


  • Education and Training: demonstration, extension, on-farm/ranch research
  • Farm Business Management: budgets/cost and returns
  • Pest Management: allelopathy, cultural control, integrated pest management
  • Production Systems: holistic management
  • Soil Management: green manures, organic matter
  • Sustainable Communities: sustainability measures


    The effects of vegetable crop rotations and residue amendment on Verticillium wilt of strawberry and marketable yield were compared with methyl bromide+chloropicrin fumigation. After four crops of vegetables and two crops of strawberry, the numbers of V. dahliae microsclerotia in broccoli plots were consistently low, while the lettuce plots were a potential reservoir of microsclerotia. At both sites broccoli rotation plots had higher strawberry plant diameter and lower Verticillium wilt severity than other treatments. At, final harvest, yield loss was 23% in broccoli rotation treatment and 39% in lettuce rotation treatment relative to the standard fumigation treatment. Data on the soil microflora suggest that rotations with broccoli increased the overall bacterial and actinomycete populations in soil by nearly a 1000-fold while rotations with lettuce did not increase these populations over the baseline levels. Mycorrhizal associations on strawberry roots under the different rotation treatments were non-existent. The cost-benefit analysis of the different rotation treatments compared with the standard fumigation treatments suggested that despite not being able to plant strawberries each year, rotations with broccoli would be profitable over the long term. Rotations with broccoli were equally effective under both conventional and organic production systems. Under moderate disease pressure, broccoli rotation has the potential to be a feasible alternative for reducing Verticillium wilt severity in strawberry.

    Project objectives:

    1. Demonstrate the effects of rotations with broccoli, brussels sprouts, cauliflower, and lettuce on strawberry yield, root infection, systemic vascular colonization, incidence of soilborne diseases on strawberry, and pathogen survival in soil.
    2. Determine if the broccoli-mediated pathogen propagule attrition and wilt suppressiveness on strawberry is due to altered soil microflora.
    3. To determine the impact of crop residue on the occurrence of arbuscular mycorrhizal symbiosis in strawberry roots.
    4. To calculate costs and benefits of sustainable alternatives such as broccoli rotational crop to chemical fumigants and to determine their relative profitability in strawberry crop system.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.