Agriculture Reference
In-Depth Information
whole plants include grey mould (
Botrytis cinerea;
Weltzien, 1989; Elad & Shtienberg,
1994, Scheuerell & Mahaffee, 2006), powdery mildews (including
Sphaerotheca
and
Uncinula
spp.; Weltzien, 1989; Elad & Shtienberg, 1994, Scheuerell, 2002), downy
mildew (
Plasmopara viticola
; Ketterer, 1990), fungal and bacterial blights/leaf spots
(caused by a range of pathogens including
Pseudopeziza tracheiphila, Sphaeropsis sap-
inea, Pseudomonas
spp. and
Xanthomonas
spp.; Weltzien, 1989; Yohalem
et al
., 1994;
Al-Dahmani
et al
., 2003) and apple scab (
Venturia inaequalis;
Yohalem
et al
., 1996).
Crops that have been studied in this context include mainly edible cereal, vegetable and
fruit crops such as maize, barley, sugar beet, potato, bean, lettuce, pepper, tomato, grape,
apple and strawberry. The feedstocks used to prepare composts from which the stud-
ied teas were prepared, varied, although most included some form of animal manure.
The compost production methods used, the type of extract/tea used and the experimental
conditions varied greatly and it was diffi cult to compare results of work carried out on
single diseases by different workers. Disease suppression in the work listed above was
extremely variable and was not recorded with all pathogens in all tests. Effi cacy depended
on the crop, the feedstocks used to make the compost, the compost production system, the
extract/tea preparation method and the experimental system used to test the extract/tea.
Defi nitions of the type of extract used in experimental work varied depending on the
authors. However, almost all of the studies involved NCTs under the defi nition adopted
in this review and that of Scheuerell & Mahaffee (2002). Several commercial companies
in the United States and Europe now promote and sell machinery to make ACTs (www.
soilfoodweb.com; www.attra.ncat.org). However, limited work has been published to date
to demonstrate the effi cacy of ACTs and there is little scientifi c evidence to show that they
are any more effective in controlling disease than NCTs.
Compost teas are also being widely advertised and used on both organic and con-
ventional farms (mainly in the United States) as an inoculant to restore or enhance soil
microfl ora (www.attra.ncat.org). However, very little work has been done to confi rm or
quantify the benefi ts from using compost teas in this way. Tränkner (1992) investigated
the effect of NCTs on seedling damping-off caused by
Pythium ultimum
. He found that
NCTs prepared from either grape marc or cattle manure suppressed mycelial growth of
P. ultimum in vitro
. He also found that application of NCTs signifi cantly increased seed
germination, root length and root dry weight when seeds were soaked in NCT and dried
prior to being sown in soil inoculated with
P. ultimum
. There has also been work done
to show that NCT suppressed the growth of
Rhizoctonia solani in vitro
(Weltzein, 1991),
but it is well known that successful disease control
in vitro
does not always translate to
fi eld conditions. Recent work has shown that Fusarium wilt of pepper (
F. oxysporum
f. sp.
vasinfectum
) and cucumber (
F. oxysporum
f. sp.
cucumerinum
) was controlled by drench-
ing NCT on to soil under greenhouse conditions (Ma
et al
., 2001). More comprehensive
accounts of diseases which have been fully or partially controlled through the application
of compost teas or extracts under experimental conditions are given in Litterick
et al.
(2004) and Scheuerell & Mahaffee (2002).
5.8.1
Factors affecting disease suppression
There is suffi cient information to show that in some cases, plant pathogen control has
been at least as good with compost extracts or teas as with conventional fungicides
