Compost has Disease Suppression Properties
"Composts, if they are prepared and handled properly, have the ability to suppress and control soil borne plant diseases."
This is at first a surprising statement to many of us, brought up as we are to believe that the presence of such a huge density and variety of micro organisms as are found in compost, would surely harbour some very unpleasant individuals amongst such a population. Fail to wash your hands on returning from the tending even the best quality compost, and who knows what disease-causing agent (pathogen) awaits you! And yet- this is not true.
Pathogen destruction, which is often considered to take place only due to the action of heat when temperature rises occur during the composting process itself, or by use of chemicals, also takes place within the microbial biomass. By referring to disease suppression we are referring to the ability of the compost's bacterial, viral, cellular and fungal organisms to suppress disease.
Mature compost has been found to control plant diseases in soil or potting media when the compost is mixed with media or soil containing pathogens. The incorporation of compost has been reported to suppress diseases caused by Phytophthora spp., Pythium spp., Fusarium spp., and Rhizoctonia solani (Hoitink et al., 1991). Yard waste compost produced in Florida has been shown to suppress plant death of papaya caused by Phytophthora palmivora (A.W. Barkdoll, D.J. Mitchell, and R.A. Nordstedt, unpublished).
The disease suppressive quality of compost does appear to be due to the microbial population of mature compost. Several bacterial and fungal species present in finished compost have been shown to be involved in disease control (Chung and Hoitink, 1990; Hardy and Sivasithamparam, 1991*). These biological control agents reportedly re-colonise compost during the second mesophilic stage which occurs after the thermophilic stage.
For compost to retain its biological control properties, it must be prepared properly and handled properly once it is mature. The alteration of the microbial population of the compost can destroy its ability to control disease. In research, when compost was micro-waved to alter its microbial population, disease suppression was lost and 100% of the plants died (A.W. Barkdoll, D.J. Mitchell and R.A. Nordstedt, unpublished*). Excessive heat alters the compost and there are indications that storing the material in plastic bags also destroys its ability to control plant disease.
We have also ourselves some experience in the use of liquid compost in the form of "Compost Teas", created by soaking and draining compost after a period of time for the successful enhancement of plant health and leaf vitality, and we believe an element of disease suppression is likely to be in part the cause of this.
We are keen to learn more about this little researched capability of compost, and wonder if this work could be developed into replacements for some of the chemical remedies, many of which are being progressively outlawed by our regulatory authorities due to their negative side effects. If you have an experience of composts suppressing disease we would like to hear from you. Email: sam.brown@enviros.com, or use our Contact Form here.
We are indebted to the Florida Co-operative Extension Service,11/91 Circular 1027. (*See http://edis.ifas.ufl.edu/HE027 ). Larry R. Arrington, Interim Dean, for the inspiration for this article.
Other links to article, papers, and sources on composts providing disease suppression are:
"Disease control from compost is suspected to occur through four pathways. These include competition for nutrients among pathogens and beneficial microorganisms, the production of antibiotics by compost microorganisms, and compost microorganisms consuming pathogens. Recent research has added a fourth pathway, turning on disease resistant genes in plants grown in compost enhanced soils or treated with compost tea." www.anr.state.vt.us/dec/wastediv/compost/ 97Summerpdf/GOLFCOURSE7.pdf
http://www.hort.uconn.edu/ipm/general/htms/composts.htm
MICROBIAL ECOLOGY OF COMPOST-INDUCED DISEASE SUPPRESSION, Nelson, E. B.1, Craft, C. M.2, and McKellar, M. E.1, Cornell University, 1Department of Plant Pathology, Ithaca, NY 14853 USA and 2Cornell SeedPotato Certification Program, Lake Placid, NY 12946 USA
Innovative Uses of Compost: Disease Control for Plants and Animals US EPA.
http://www.oardc.ohio-state.edu/michel/diseasesuppression.htm
http://ohioline.osu.edu/cd-fact/0160.html
http://www.dpw.wau.nl/biob/research/proj15.htm
Compost tea: principles and prospects for disease control, By Craig Coker, Council President
Chasing consistent disease suppression in potting media By Dr Peter Fahy
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