Anaerobic soil disinfection (ASD) is a biological alternative to pre-plant fumigation, in which the processing of carbon inputs under flooded conditions creates anaerobic conditions and shifts the microbial community toward facultative and obligate anaerobes over several weeks. The addition of a labile carbon source stimulates microbial growth and respiration; irrigation fills soil pore spaces with water, and tarping with plastic or rolling the topsoil limits gas exchange. During this process, the decomposition by-products diffusing through the soil solution and rapid growth of aerobic microorganisms both reduce soil oxygen levels. Various forms of ASD are currently practiced primarily in Japan, The Netherlands and the US, providing effective control, in many cases, of a wide range of pathogens and nematodes. However, the effect of ASD on insect pests has never been assessed.
We buried cabbage root fly pupae (Diptera: Anthomyidae: Delia radicum) in lab and field trials with Brussels sprouts growers who have depended on fumigants since the 1950s to prevent the build-up of pest populations and allow continuous cropping of sprouts in the Central Coast region of California. In both cases, we found significant reductions in sentinel fly pupal survival in soil after ASD compared to control soils and comparable to or improving on the effects of fumigation. ASD methods manage and use microbial communities to provide biological control of pests and pathogens, which is a radical departure from prior practices that use toxins to sterilize the soil of all biota.