Compost Teas: Alternatives to Traditional Biological Control Agents

Authors: Mahaffee, Walter - Walt; SCHEUERELL, STEVE - OREGON STATE UNIVERSITY

Submitted to: Microbial Ecology of Aerial Plant Surfaces
Publication Type: Book / Chapter
Publication Acceptance Date: 11/23/2005
Publication Date: 10/31/2006
Citation: Mahaffee, W.F. and Scheuerell, S. 2006. Compost teas: Alternatives to traditional biological control agents. In: Baily, M.J., Lilley, A.K., Timms-Wilson, T.M., and Spencer-Phillips, P.T.N. editors. Microbial Ecology of Aerial Plant Surfaces. Oxford, England: CABI. p.165-179.

Interpretive Summary: In many areas of plant production, practitioners are looking for alternatives to synthetic pesticides and commercial biocontrol agents. Compost teas are being extensively used in urban, horticultural and agricultural settings for their fertility and disease control properties. There are two main methods of compost tea production, aerated (ACT) and nonaerated (NCT), both of which require that compost be mixed with or placed in water for a period of time. NCTs are generally incubated undisturbed for 1-14 days prior to filtering and application. ACTs are either recirculated or injected with air and incubated for 24-36 h prior to filtering and application. While the popular press is replete with anecdotal indications of the efficacy and claims of superiority of ACTs, there has been, until recently, little critical investigation of these claims. There were no differences in disease control afforded by ACTs and NCTs when using the same compost source. However, compost source was the most important factor in controlling several diseases. The addition of some nutrients (e.g., kelp and humic acid) enhanced disease control while the addtion of others (e.g., molasses) decreased disease control. The addition of adjuvants to enhance droplet dispersion and adherence also increased disease control. The control efficacy of compost teas is similar to that of commercial biocontrol agents. For some diseases, the level of control would be considered inadequate for conventional agriculture; however, organic producers with limited control options consider partial disease control to be an important improvement. Further refinement of compost and compost tea production will likely increase the potential for consistent disease suppression with compost tea applications.

Technical Abstract: In many areas of plant production, practitioners are looking for alternatives to synthetic pesticides and commercial biocontrol agents. Compost teas are being extensively used in urban, horticultural and agricultural settings for their fertility and disease control properties. The majority of the information available on their production and use is anecdotal since they have received only limited scientific investigation. There are two main methods of compost tea production set apart by whether the compost water mixture is aerated or not. Both methods require that compost be mixed with or placed in water for a period of time. Nonaerated compost teas are generally incubated undisturbed for 1-14 days prior to filtering and application. Weltsien and Trankner extensively investigated the use of nonaerated compost teas for the control of numerous foliar and soil borne diseases with mixed results. Aerated compost teas are either recirculated or injected with air and incubated for 24-36 h prior to filtering and application. While the popular press is replete with anecdotal indications of the efficacy and claims of superiority of aerated teas, there has been, until recently, little critical investigation of these claims. Over the past six years we have investigated the efficacy of nonaerated and aerated compost teas for the control of both foliar and soil-borne diseases of several hosts. There were no differences in disease control afforded by aerated and nonaerated compost teas when using the same compost source. However, compost source was the most important factor in controlling Botrytis cinerea, Podosphaera pannosa, and Diplocarpon rosae, but not important for suppressing Pythium damp-off. The addition of nutrients in some cases (e.g., kelp and humic acid) enhanced disease control while in some instances (e.g. molasses) decreased disease control. The addition of adjuvants to enhance droplet dispersion and adherence also increased disease control of foliar pathogens. The control efficacy of compost teas is similar to that of commercial biological control agents. For some diseases, the level of control would be considered inadequate for conventional agriculture; however, organic producers with limited control options consider partial disease control to be an important improvement. Further refinement of compost and compost tea production will likely increase the potential for consistent disease suppression with compost tea applications.