Alternatives to Soil Fumigants
Control of soil-borne pathogens, nematodes and weed pressure in a wide variety of cropping systems has traditionally been achieved with soil-applied fumigants. Methyl Bromide has long been the principle fumigant, but increased awareness of its environmental impact led to its phase out beginning in 1993 and terminating in 2005. Alternative chemical treatments such as chloropicrin (Telon) and metam sodium (Vapam) products have since taken the place of methyl bromide. Persistent issues with environmental fate and efficacy of chemical fumigants has spurred research into organic soil disinfestation practices. Soil solarization, flooding and steaming have been organic alternatives developed to reduce nematodes, soil pathogens and weed seed viability, but are not always effective or feasible. As a result, anaerobic soil disinfestation (ASD) has been developed which incorporates aspects of both solarization and flooding. A recent field day at the UC Kearney Ag Center in Parlier, CA compared treatments of Telone C35 and ASD on tree crop replants. ASD treatments utilizing rice bran and/or sudan grass as carbon sources compared very favorably to Telone C35 treatments when re-establishing prunus species.
Soil disinfestation was developed in the Netherlands (Blok, et al. 2000) and in Japan (Shinmura, 2000). ASD is based on incorporating an organic carbon source, irrigating to saturation, then tarping with an oxygen impermeable layer. These conditions exploit native soil microbes that thrive in anaerobic conditions and accumulate toxins suppressing a broad range of fungi, nematode, weeds and other microorganisms. The practice was further adapted to coarse soils (Rosskopf, et al 2010; Butler, D.M. et al 2009) by incorporating additional organic carbon sources such as poultry litter and molasses to reduce leaching and maintain anaerobic conditions on sandy, low-saturation soils. The practice results in a reduction or elimination of pests of concern, but not complete elimination of all soil microorganisms. ASD differs from soil solarization in that reliance on thermal effects isn’t the driver for pathogen suppression. Rather, the process relies on anaerobic microorganism populations to create unfavorable conditions for certain soil-borne pests. Anaerobic conditions and toxin build-up are then reversed when tarps are pulled or soils are dried. ASD showed good efficacy on fusarium, rhizoctonia, and verticillium after 15 weeks of tarping (Blok et al, 2000). Overall, suppression of plant pathogenic nematodes, weeds and phytopthora, as well as the subsequent yield response, are similar to results achieved by using methyl bromide in at least one southeastern U.S. study (Butler, D.M. et al, 2009).
-Ben Cantrell, Northern California Agronomist
References
Blok W.J., Lamers J.G., Termorshuizen A.J., Bollen G.J. 2000, Control of soilborne plant pathogens by incorporating fresh organic amendments followed by tarping. Phytopathology 90, 253-259.
Butler, D.M., Rosskopf, E.N., Kokalis-Burelle, N., Muramoto, J., Shennan, C. 2009 Field evaluation of anaerobic soil disinfestations in a bell pepper-eggplant double crop. Proc. Annual Int. Res. Conference on Methyl Bromide Alternatives and Emissions Redctions. MBAO, p. 43.1-43.4
Harr, M.J., Fennimons, S.A., Ajwa, H.A., Winterbottom, C.Q., 2002, Cloropricrin effect on weed seed viability, Crop Prot. 22, 109-115.
Kokalis-Burelle, N., Butler, D.M., Rosskopf,E.N. 2013, Evaluation of cover crops with potential for use in anaerobic soil disinfestation (ASD) for susceptibility to three species of meloidogyne. J. of Nematology 45, 272-278
McCarty, D.G. Anaerobic Soil Disinfestation: Evaluation of Anaerobic Soil Disinfestation (ASD) for Warm-Season Vegetable Production in Tennessee. 2012 Master's Thesis, University of Tennessee, http://trace.tennessee.edu/utk_gradthes/1393
Shinmura, A. 2000, Causal agent and control of root rot of welsh onion. PSJ Soilborne Disease Workshop Report, 20,133-143
Shinmura, A. 2004, Principle and effect of soil sterilization method by reducing redox potential of soil. PSJ Soilborne Disease Workshop Report, 22,2-12
Zasada,I.A., Halbrent, J.M., Kokalis-Burelle, N., LaMondia, J., McKenry, M.V., Noling, J.W. 2010, Managing nematodes without methyl bromide. Annual Review of Phytopathology 48, 311-328