Integrating Compost Teas in the Management of Fruit and Foliar Diseases for Sustainable Crop Yield and Quality - Composting for Sustainable Agriculture - page 172

aerobic microorganisms (Ingham 2005 ; Palmer et al. 2010b ). Filtration is achieved
through use of a porous bag or screen. Practitioners often amend ACT with nutrients
or adjuvants during or after preparation (Scheuerell and Mahaffee 2004 ). The per-
ceived benefits, efficacy and safety of these practices are explored in later sections.
NCT takes anywhere between 3 and 14 days to produce and may be filtered
after the extraction period (Koné et al. 2010 ; Scheuerell and Mahaffee 2002 ). NCT
is associated with lower production costs and energy input, and is more likely to
be used in regions where there is no electricity or the cost of energy is prohibitive.
The generally faster production times for ACT have seen a plethora of commercial
businesses establish to provide specialised equipment and services to high-input
agriculture and horticulture in the USA, Europe and Australia (Anonymous 2006 ;
Diver 2002 ).

9.3 Compost Teas as a Form of Biological Control

In order to understand potential levels of disease suppression with compost teas,
it is worth considering the effectiveness of biological control more generally. A
number of single species tested for biological control have been reported to be as
effective as programs that use synthetic chemicals when applied in controlled en-
vironments such as greenhouses (Dik and Elad 1999 ; Elad et al. 1993 ; Guetsky
et al. 2001 ). Indeed, compost is sometimes used as a substrate to propagate fungal
biocontrol agents (Metcalf 2002 ; Ramona and Line 2002 ). In contrast, results under
variable field conditions have been inconsistent and associated with disease sever-
ity observed in non-treated areas (Bisiach et al. 1985 ; Gullino and Garibaldi 1988 ).
Single species may be constrained by mechanism of action (see Sect. 9.5), and/or
environmental conditions such as temperature and surface-wetness duration that
can affect spore germination and growth rates relative to the plant pathogen. One
strategy has been to incorporate two or more biological agents to increase disease
suppression (Guetsky et al. 2001 ; Stewart 2001 ).
In what appears to be the first scientific report about compost teas, Hunt et al.
( 1973 ) described how watery extracts of composted municipal refuse induced im-
mobility in sting nematodes. Another foundational study used NCTs to suppress
grapevine downy mildew, caused by the biotroph Plasmopara viticola , whereby
NCT was applied to detached leaves from glasshouse-grown grapevines prior to
inoculation (Weltzien and Ketterer 1986 ). Since then, disease suppression by ACTs
and NCTs has been reviewed by several authors (Litterick et al. 2004 ; Scheuerell
and Mahaffee 2002 ; Weltzien 1990 ). There are also a number of reports that con-
clude some teas are ineffective in terms of disease control (Al-Mughrabi 2006 ;
Scheuerell and Mahaffee 2004 ; Sturz et al. 2006 ; Welke 2004 ). Where disease sup-
pression has been demonstrated, the fungal pathogens causing disease were either
biotrophic or necrotrophic in mode of nutrition (Elad and Shtienberg 1994 ), or, less
frequently, bacterial plant pathogens (Al-Dahmani et al. 2003 ; Zhang et al. 1998 ).
In systematic comparisons of NCTs and ACTs, aerating compost tea did not
significantly increase disease suppression when compared with results for NCTs