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

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

Summary

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.

2. 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.

3. 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.

Accomplishments/Milestones

In 2006 all project participants were contacted to let them know that the project had been funded; a search was conducted for a research assistant and the successful candidate was hired in December; and an advisory committee consisting of growers and county extension agents was formed.

Field and laboratory screening assays were initiated to test 47 brassica accessions obtained from the National Germplasm Repository for biofumigation potential. Species include Brassica napus (rutabaga ancestor), B. juncea (Indian mustard), B. rapa (field mustards and Chinese cabbage), B. carinata (Ethiopian mustard), and Eruca sativa (arugula). All accessions were planted in summer and fall (with and without cover), to test germination, survival, biomass production, and days to flowering. Most accessions were frost tolerant, surviving lows of 15 ºF but not 0 ºF.

Accessions that consistently demonstrated early maturity, superior biomass production, and cold tolerance have been identified as possible cover crops, and are being tested for glucosinolate content and ability to inhibit P. capsici and S. sclerotiorum survival in the laboratory. In 2006 we developed, adapted, and tested methods for reliably producing germinable oospores of P. capsici, which will be used in these assays.

A preliminary field study conducted in 2006 demonstrated control of S. sclerotiorum in two commercial high tunnels using solarization through July and August. None of the 800 sclerotia buried in solarized plots germinated; approximately half of those buried in untreated plots or plots treated with the commercial biocontrol Contans WG germinated. A manuscript outlining the methods and results of this study has been prepared for submission to the online publication Plant Disease Management Reports.

The project was discussed in a front-page local newspaper story (Frankfort State Journal, April 27, 2006). A tour of the Kentucky State University high tunnel on October 19th 2006 attracted 24 people to discuss diagnosis and organic management options for S. sclerotiorum in high tunnels.

Impacts and Contributions/Outcomes

This research will serve both organic and conventional vegetable growers by developing disease-management strategies that are compatible with organic standards, but also fit within conventional production systems. The project will generate recommendations that 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. Our findings and recommendations will be disseminated through extension publications, farm tours, field days, and scientific journal articles to reach a broad spectrum of vegetable growers and agricultural scientists. Successful disease management tactics generated by this research will encourage Kentucky farmers to consider vegetable production as a high value alternative to tobacco.

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