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.
- 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.
- Found glucosinolate concentration was highest in aboveground tissue of field-grown mustards (~70 umol/g), moderate in high tunnel-grown mustards (~40 umol/g), and lowest in greenhouse-grown mustards (~25 umol/g).
Found ‘Pacific Gold’ mustard variety offered a superior combination of biomass production, cold tolerance, and glucosinolate production, relative to other mustards tested.
- Found that high tunnel plantings of ‘Pacific Gold’ mustard offer superior biomass production when planted in March-April for May incorporation, but can survive heat of high tunnel in mid-summer if irrigated regularly. Mustards planted June 30th produced 0.6 kg of fresh aboveground biomass per square meter for incorporation into soil on August 5th.
Found that solarization through August in the high tunnel completely inhibited germination of soil-borne S. sclerotiorum sclerotia.
Found that incorporation of high-tunnel grown ‘Pacific Gold’ mustard offered no more inhibition of sclerotia than incorporation of high-tunnel grown buckwheat.
Found no effect of pulverized ‘Pacific Gold’ mustard incorporation rate (0-16 kg/m2) on germination of S. sclerotiorum in high tunnel soil. High rates required gloves and goggles to handle.
Found no significant effect of solarization or biofumigation on soil microbial activity, as measured by Fluorescein diacetate hydrolysis of soil after treatment.
- Found inverse correlation between ‘Pacific Gold’ mustard incorporation rate (0-16 kg/m2) and growth of yellow squash seedlings, but no evidence that biofumigation inhibited P. capsici in soil.
Used spring planting of yellow squash to build disease pressure before summer cover crops of ‘Pacific Gold’ mustard and/or buckwheat were grown to flower and incorporated into soil in preparation for fall planting of yellow squash. 85% of second yellow squash crop was killed by P. capsici, with no significant effect of previous cover crop on disease incidence.
- Research assistant Brian Geier stands next to a six-week old stand of ‘Pacific Gold’ mustard planted in a high tunnel in March (left). The spring-planted mustard grew more than twice as high as the same variety planted outside (top right) or inside (bottom right) the same high tunnel in June.
- Proportion of S. sclerotiorum sclerotia in high tunnel soil surviving incorporation of a mustard or buckwheat cover crop on August 5th, 2009 followed by a month with, or without, solarization.
- Average daily temperature flux in solarized and unsolarized soil.
Impacts and Contributions/Outcomes
- Brian Geier, Michael Bomford, Paul Wiediger, Paul Vincelli and George Antonious. Sustainable Soil-Borne Disease Management presentation, Southern Sustainable Agriculture Working Group High Tunnel Short Course. Chatanooga, TN, 01/22/09. (http://organic.kysu.edu/SSAWG2009.pdf)
Michael Bomford. Organic Agriculture at Kentucky State University. Third Thursday Thing, Organic Agriculture Day, Frankfort, KY, 02/19/09. (http://organic.kysu.edu/OrganicTTT2009.pdf)
Abdul Kakar, Michael Bomford and Brian Geier. Effectiveness of a Blend of Beneficial Microorganisms and Brassica Green Manures in Reducing Damage by Phytophthora capsici to Yellow Squash (Curbita pepo) Seedlings. Bio 410 Seminar Series, Kentucky State University, Frankfort, KY, 03/06/09. (http://organic.kysu.edu/Abdul-Phytophthora.pdf)
Michael Bomford, Paul Vincelli, George Antonious, and Kenny Seebold. Managing Sclerotinia sclerotiorum in High Tunnels with Biofumigation and Solarization. Plant Pathology Seminar Series, University of Kentucky, Lexington, KY, 03/09/09. (http://organic.kysu.edu/UKPathologySeminar.pdf)
Michael Bomford. Organic Growing. Henderson County Master Gardeners’ Class, Henderson, KY, 03/19/09. (http://organic.kysu.edu/HendersonOrganicGardeners.pdf)
Michael Bomford, Paul Vincelli, George Antonious, Brian Geier and Ed Dixon. Solarization and biofumigation for organic control of white mold in high tunnels. American Society for Horticultural Science Meeting, St. Louis, MO, 07/27/09. (http://ashs.org/db/horttalks/detail.lasso?id=685)
Brian Geier, Michael Bomford, Paul Vincelli, and George Antonious. Effect of Biofumigation and Soil Solarization on Sclerotinia sclerotiorum in High Tunnel Vegetable Production Systems of Kentucky. Kentucky Academy of Science Meeting, Highland Heights, KY, 11/14/09. (http://organic.kysu.edu/Geier-KAS2009-Biofumigation.pdf)
- Grower cooperators and other growers with established high tunnels have started incorporating solarization periods and mustard plantings into high tunnel rotations.
At least 5 farmers who have attended our workshops have been inspired to erect high tunnels.
- Three undergraduate students received hands-on training in research techniques through involvement with this project.
Project participants routinely respond to inquiries about about solarization, biofumigation, soil-borne disease management and winter vegetable production.
Extension Plant Pathologist
University of Kentucky
205 Plant Science Building
1405 Veterans Drive
Lexington, KY 40546
Office Phone: 8592577445
Extension Professor - Plant Pathology
University of Kentucky
University of Kentucky
207 Plant Science Bldg
Lexington, KY 40546-0312
Office Phone: 8592577445