Biofumigation for soil health in organic high tunnel and conventional field vegetable production systems

2007 Annual Report for LS06-185

Project Type: Research and Education
Funds awarded in 2006: $170,000.00
Projected End Date: 12/31/2009
Region: Southern
State: Kentucky
Principal Investigator:
Dr. Michael Bomford
Kentucky State University

Biofumigation for soil health in organic high tunnel and conventional field vegetable production systems


This project tests biofumigation – a soil-borne disease management strategy using natural chemicals from brassicas – as a control for two broad-spectrum diseases that each pose a severe challenge to a different emerging vegetable production system in Kentucky. The fungus Sclerotinia sclerotiorum thrives in cool conditions, and attacks most of the crops grown in a system developed by Kentucky growers to produce organic vegetables year-round in solar heated high tunnels. Another fungus, Phytophthora capsici, spreads in warm weather and attacks many of the crops grown by the increasing number of farmers switching from tobacco to field vegetable production in our region. We hypothesize that biofumigation can be adapted to both the high tunnel and field vegetable system to manage these diseases while building soil organic matter and enhancing soil microbial activity. We are conducting a series of laboratory studies to identify promising biofumigant crops for each disease, followed by on-farm field trials adapting the biofumigation strategy to each system. This research responds to specific emerging disease threats and addresses two of the most important research topics identified by local growers in a survey distributed at a SARE-funded workshop.

Objectives/Performance Targets

  1. Identify brassica varieties that inhibit survival and growth of S. sclerotiorum and P. capsici in lab-based bioassays.Determine the potential of brassica residue incorporation and solarization – alone and in combination – to reduce disease pressure from S. sclerotiorum and build biologically active soils in high tunnels used for year-round vegetable production.

    Determine the potential for brassica and non-brassica winter cover crops to reduce disease pressure from P. capsici and build biologically active soils in field vegetable production systems.


Objective 1 Accomplishments
  • Found glucosinolate content of mustard greens grown in field, high tunnel, and greenhouse conditions averaged 77, 40 and 25 micromoles per gram fresh weight, respectively. Repeated greenhouse and field studies.Identified ‘Pacific Gold’ mustard as a superior variety, relative to other accessions tested, in terms of yield, cold tolerance, glucosinolate content, and inhibition of pathogens.

    Calculated dose response of S. sclerotiorum sclerotia to mustard greens in lab-based assays. A concentration of 0.16 g of fresh mustard greens per mL of soil killed half of the sclerotia tested. Repeated test in Petri dishes and in plant pots.

    Found that P. capsici is almost completely inhibited at all concentrations tested, suggesting it is more susceptible to biofumigation than S. sclerotiorum

    Found that ‘Pacific Gold’ mustard planting date is related to amount of biomass produced by flowering, with biomass production declining between April and June. Concluded that early spring planting is best for production of ‘Pacific Gold’ mustard as a biofumigant crop.

Objective 2 Accomplishments
  • Repeated study measuring effect of burial depth and treatment period on soil temperature and sclerotial susceptibility to biofumigation and solarization in commercial high tunnels.Confirmed effectiveness of summer solarization for one month, which killed 100% of sclerotia 5 cm below the surface and 93% of sclerotia 15 cm below the soil surface.

    Confirmed that biofumigation with 1 kg of B. juncea per square meter did not reduce sclerotial survival.

    Measured extracellular enzyme activity of solarized and unsolarized soils after 2 and 6 weeks of solarization.

    Confirmed that summer solarization in high tunnels boosts average daily high and low soil temperatures by 8-10 C and 4-5 C, respectively, in the top 15 cm.

Objective 3 Accomplishments
  • Evaluated potential of ‘Pacific Gold’ mustard as a spring-planted cover crop, to be incorporated before transplanting warm-season vegetables. Found that late April planting produced more biomass than late June planting.Recorded no reports of P. capsici in Kentucky field vegetables in summer of 2007 or 2008 (consecutive drought years). Unsuccessful attempt to inoculate university research land with P. capsici to provide suitable site for field studies. We are again attempting to conduct this field study on inoculated land in 2009.

Impacts and Contributions/Outcomes

Impact: More than 130 people attended workshops, tours, and presentations discussing this project
  1. Solarization for organic control of white mold in high tunnels. Kentucky Fruit and Vegetable Conference and Trade Show, Lexington, KY. 01-08-08 ( Soil-Borne Disease Management: A Study of the Effects of Soil Solarization and Biofumigation on Sclerotinia sclerotiorum. Southern Sustainable Agriculture Working Group Meeting – Au Naturel Farm Field Trip, Smiths Grove, KY. 01-16-08 (

    Effect of Planting Date on Biomass Production by Brassica juncea var. ‘Pacific Gold’ Cover Crops. Kentucky Academy of Science Meeting, Lexington, KY. 11-01-08 (

    Effect of Glucosinolate Exposure on Sclerotinia sclerotiorum and Phytopthora capsici. Kentucky Academy of Science Meeting, Lexington, KY. 11-01-08 (

    A Simplified Procedure for Glucosinolate Quantification. Kentucky Academy of Science Meeting, Lexington, KY. 11-01-08 (

    Vegetable Production in High Tunnels. Fairview Produce Auction, Christian County, KY. 12-10-08 (

Impact: Preliminary results posted to website that attracted 26,000 hits in 2008
  • Organic control of white mold in Kentucky high tunnels. Streaming video. 13 minutes. ( Study Results: Biofumigation and Soil Solarization. (
Impact: Scientific and Popular Press Publications
  • M.K. Bomford, P.C. Vincelli, E.W. Dixon, and B.A Geier. 2007. Evaluation of solarization and Contans WG for control of Sclerotinia sclerotiorum in high tunnels, 2006. Plant Disease Management Reports 1: V163.M.K. Bomford, A.F. Silvernail and B.A. Geier. 2007 (Abstract). Season extension with high tunnels in Kentucky. HortScience 42(4): 988.

    Sara Gividen. High Life Helps Plants Survive Low Temps. Frankfort State Journal, p. A1. 04/18/2007.

Other impacts and outcomes
  • Grower cooperators Paul and Alison Wiediger and several other high tunnel growers in Kentucky have altered their production systems to include a period of summer solarization for management of S. sclerotiorum.Undergraduate student John Rodgers received hands-on training in research techniques through his involvement with this project.

    Project participants have received numerous requests for information about winter vegetable production in Kentucky.

    The number of certified organic farms in Kentucky doubled (from 26 to 52) in 2007.

    We expect recommendations generated by this research to enhance the sustainability of vegetable production systems by building soil health, reducing the need for external inputs, and allowing diverse crop rotations that include the many crops susceptible to P. capsici and S. sclerotiorum.

    We anticipate that new disease management tactics generated by this project will encourage Kentucky farmers to consider vegetable production as a high value alternative to tobacco.


Kenneth Seebold
Extension Plant Pathologist
University of Kentucky
205 Plant Science Building
1405 Veterans Drive
Lexington, KY 40546
Office Phone: 8592577445
Alison Wiediger
Au Naturel Farm
3298 Fairview Church Road
Smiths Grove, KY 42171
Office Phone: 2707494600
Paul Wiediger
Au Naturel Farm
3298 Fairview Church Road
Smiths Grove, KY 42171
Office Phone: 2707494600
George Antonious
Principal Investigator - Water Quality
Kentucky State University
Community Research Service
400 East Main St.
Frankfort, KY 40601
Office Phone: 5025976005
Paul Vincelli
Extension Professor - Plant Pathology
University of Kentucky
University of Kentucky
207 Plant Science Bldg
Lexington, KY 40546-0312
Office Phone: 8592577445