- Vegetables: tomatoes
- Crop Production: tissue analysis
- Education and Training: demonstration
- Pest Management: biological control, botanical pesticides, mulching - plastic, prevention, row covers (for pests)
- Production Systems: holistic management
- Soil Management: green manures
We investigated the potential of Brassica species as a biofumigation cover crop for control of soilborne disease in tomato production. In a laboratory jar test, Indian mustard inhibited mycelial growth of Sclerotium rolfsii, the fungal agent that causes Southern blight of tomatoes. In field trial, Brassica cover crops (B. juncea L and B. campestris) grew over winter and were tilled into the soil the following spring. In Spring 2000, marketable tomato fruit yield was significantly higher in the Brassica treated plots than in the control plots treated with rye. In Summer 2001, marketable tomato fruit yield was not significantly different between treatments. In an additional laboratory study, individual isothiocyanates (ITCs) (one of the active compounds released from the Brassica species) were assayed for activity against selected plant pathogens and potential synergistic effects were investigated. Results suggested that there were differences in pathogen sensitivity to the compounds studied. Additive and synergistic effects were observed when combinations of ITCs, suggesting that some of the effects seen with the uses of whole tissue application maybe due to a combination of chemicals instead of the dominate ITC present.
Methyl Bromide (MeBr) is necessary in tomatoes production to maintain profitable yields under intensive cultivation. This broadspectrum pesticide is extremely lethal and kills most organisms with which it comes in contact. It has no selectivity to pathogens; instead it produces a near sterile environment removing beneficial organisms as well as pathogens. In addition to the ecological imbalance it imposes on the application site, questions have been raised about its effect on surrounding ecosystems as it volatilizes into air. It is however, methyl bromide’s potential as an ozone-depleting agent that has led to the ban enforced by the EPA and parties of the Montreal Protocol (E.P.A., 1997).
Loss of MeBr may prove devastating to many agricultural communities. A study by the U.S. Department of Agriculture and state universities assessed the effects of potential restrictions of MeBr. The findings, based on agriculture in California, Florida, Georgia, Kentucky, North Carolina and Tennessee, estimated about $1 billion lost annually in growers’ net revenue and consumer cost. Regional and national effects will be visible in the lower quantity and quality of produce available for consumption (Ferguson and Padula, 1994).
The glucosinolate/myrosinase system found in Brassica spp is a natural defense mechanism (Siemens and Mitchell-Olds, 1998). Maceration of plant material causes the mixing of glucosinolate with myrosinase; myrosinase degrades glucosinolates to isothiocyanates that produce the pungent flavor associated with cole crops such as broccoli, cabbage and Brussels sprouts. In controlled laboratory experiments, the pesticidal qualities of isothiocyanates have been proven (Al-Khatib et al., 1997; Charron and Sams, 1999; Harvey et al., 2002; Mayton et al., 1996; and Mojtahedi et al., 1993).
Non-chemical alternatives to MeBr will serve to reduce the potential environmental impact of synthetic pesticides. Biofumigation with Brassica species may provide viable alternative and when incorporated within an Integrated Pest Management system may provide an effective, sustainable regime of disease control.
The overall objective of this study is to determine the feasibility of Brassica sp. green manures as a natural alternative to methyl bromide. Pursuant with this goal, many factors were investigated. This study looked at the ability of mustard-biofumigation to control individual soilborne pathogens. and the relationship of isothiocyanate production and pathogen control. The field study investigated implementation of biofumigation in field settings and looked at its integration with sustainable agricultural systems. Additionally, isolation of individual glucosinolates and determination of the lethality of each specific isothiocyanate was completed to aid in screening Brassica sp. for field use.