An increasing number of greenhouses are reusing nutrient solutions in their operations to protect the environment and save water and fertilizer (Richard et al., 2006). One major concern of this practice is the risk of dispersal of soil- and water-borne plant pathogens within the recirculation system (Richard et al., 2006). Various water disinfection technologies have been used in controlled environment plant production systems including greenhouse and nursery operations. However, these technologies are usually ineffective in controlling pathogens in potting substrates, especially when the substrates contain organic materials. For example, the frequently used oxidants (e.g., ozone, chlorine, and chlorine dioxides) may react with organic potting substrates before they reach residual levels that are lethal to plant pathogens. Similarly, control of plant pathogens with copper ion is also challenging because organic potting substrates can bind copper ions, preventing them from reaching critical levels for pathogen control (Zheng et al., 2004).
An alternative to nutrient solution disinfestation technologies in controlled environment plant production systems to reduce pathogen pressure in reused nutrient solution is the use of pathogen-suppressing growing substrates and the addition of beneficial microorganisms.
Compost teas (water extracts from the fermentation of compost materials) have been reported to act as natural pesticides and may contain various biopesticidal microbes and organic chelators (Scheuerell and Mahaffee, 2002). Using composted organic materials such as municipal wastes, hardwood bark, and vermicompost as soil amendments have been shown to reduce root rot diseases (Dissanayake and Hoy, 1999; Hoitink et al., 1991; Szczech, 1999; Trillas-Gay et al., 1986).
More than 10 yeast genera were used to control soilborne plant diseases (El-Tarabily and Sivasithamparam, 2006). Yeasts are required for beer brewing and are often removed, in conjunction with other unwanted solids, at the end of the brewing process by filtration through powdered DE. We are not aware of any work designed to investigate the potential of using liquid from DE slurry to control plant pathogens.
During a survey of the status of greenhouse nutrient solution recirculation in Ontario, Canada (Richard et al., 2006), it was found that some greenhouses had been reusing their nutrient solutions for more than 20 years without increased disease incidence. Microbiological analysis of some of these nutrient solutions did not detect any plant pathogens (data not shown).
The objective of this study was to evaluate the inhibitory potential of three compost teas (pine bark, manure, and vermicasting), Root Rescue Landscape Powder® (a mix of mycorrhizae and other beneficial microbes), waste DE from beer brewing, and a greenhouse nutrient solution that had been reused for more than 20 years on six water- or soil-borne plant pathogens commonly found in Ontario greenhouses.
AdamG.DuncanH.2001Development of a sensitive and rapid method for the measurement of total microbial activity using fluorescein diacetate (FDA) in a range of soilsSoil Biol. Biochem.33943951
BoehmM.J.HoitinkH.A.J.1992Sustenance of microbial activity in potting mixes and its impact on severity of Pythium root rot of poinsettiaPhytopathology82259264
Boyd-WilsonK.S.H.WalterM.2002Suppression of fusarium seedling blight by composted and uncomposted radiata pine barkAustralas. Plant Pathol.315761
ChetI.1987Trichoderma-application mode of action and potential as a biocontrol agent of soilborne plant pathogenic fungi p. 137–160. In: Chet I. (ed.). Innovative approaches to plant disease control. Wiley New York NY
DissanayakeN.HoyJ.W.1999Organic material soil amendment effects on root rot and sugarcane growth and characterization of the materialsPlant Dis.8310391046
El-MehalawyA.A.2004The rhizosphere yeast fungi as biocontrol agents for wilt disease of kidney bean caused by Fusarium oxysporumIntl. J. Agr. Biol.6310316
El-TarabilyK.A.2004Suppression of Rhizoctonia solani diseases of sugar beet by antagonistic and plant growth-promoting yeastsJ. Appl. Microbiol.966975
El-TarabilyK.A.SivasithamparamK.2006Potential of yeasts as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promotersMycoscience472535
GerdemannJ.W.1975Vesicular–arbuscular mycorrhizae p. 575–591. In: Torrey J.G. and D.T. Clarkson (eds.). The development and function of roots. Academic Press London UK
HanD.Y.CoplinD.L.BauerW.D.HoitinkH.A.J.2000A rapid bioassay for screening rhizosphere microorganisms for their ability to induce systemic resistancePhytopathology90327332
HoitinkH.A.J.InbarY.BoehmM.J.1991Status of compost-amended potting mixes naturally suppressive to soil borne diseases of floricultural cropsPlant Dis.75869873
KayeJ.W.PflegerF.L.StewartE.L.1984Interaction of Glomus fasciculatum and Pythium ultimum on greenhouse-grown poinsettiaCan. J. Bot.6215751579
KettererN.1990Studies on the effect of compost extracts on the leaf infestation of potato and tomato by Phytophthora infestans and on infection of grapevine by Plasmopara viticolaPseudopeziza tracheiphila and Uncinula necator. Doctoral Dissertation. University of Bonn Germany
KrauseM.S.MusselmanC.A.HoitinkH.A.J.1997Impact of sphagnum peat decomposition level on biological control of rhizoctonia damping-off of radish induced by Flavobacterium balustinum 299 and Trichoderma hamatum 328Phytopathology87S55
Margolles-ClarkE.HayesC.K.HarmanG.E.PenttilaM.1996Improved production of Trichoderma harzianum endochitinase by expression in Trichoderma reeseiAppl. Environ. Microbiol.6221452151
RichardS.ZhengY.DixonM.2006To recycle or not to recycle? Greenhouse Canada December:20–25
SchnürerJ.RosswallT.1982Fluorescein diacetate hydrolysis as a measure of total microbial activity in soil and litterAppl. Environ. Microbiol.4312561261
Trillas-GayM.I.HoitinkH.A.J.MaddenL.V.1986Nature of suppression of fusarium wilt of radish in a container medium amended with composted hardwood barkPlant Dis.7010231027