Agriculture Reference
In-Depth Information
household wastes (Schueler
et al
., 1989), green waste (or yard trimmings, Scheuerell
et al
., 2005) or hardwood bark (e.g. Nelson
et al.
, 1983; Stephens & Stebbins, 1985).
The most notable commercial use of composts to suppress plant disease concerns the
use of composted bark in the United States container-produced ornamentals sector. The
concept of using composted hardwood bark as a peat substitute to control soil-borne
pathogens on ornamental crops was fi rst suggested by Hoitink (1980). Growing media
based on composted bark was shown to suppress several soil-borne plant pathogens
including
Phytophthora, Pythium
and
Rhizoctonia
spp. which cause damage to plants
grown in container media (Spring
et al
., 1980; Nelson
et al
., 1983).
A considerable amount of work has since been done in the United States to develop
reliable suppressive container media containing composted bark for different crops and
production systems (Hoitink, 1980; Kuter
et al
., 1983; Nelson
et al
., 1983; Hoitink &
Fahy, 1986; Mandelbaum
et al
., 1988; Hoitink
et al
., 1997). It is now recognized that the
control of root rots caused by some plant pathogens (e.g.
Phytophthora
and
Pythium
) on
plants grown in compost-amended substrates can be as effective as if they were treated
with modern synthetic fungicides (Ownley & Benson, 1991). These media are now widely
used either exclusively or as part of an integrated strategy to prevent and control root
and soil-borne pathogens of container produced ornamental plants in the United States.
However, such practices are little understood and rarely used by European growers.
Most reports of disease suppression following application of composts to fi eld soils
have been carried out in containers under controlled laboratory or glasshouse conditions.
For example, Serra-Wittling
et al
. (1996) studied the effect of municipal solid waste
(MSW) compost on the half life time of fl ax seedlings grown in soil inoculated with
Fusarium oxysporum
f. sp.
lini
. It was found that the addition of 10, 20 and 30% (by
volume) of MSW to soil increased the half-life time (HLT) of fl ax seedlings to 67, 87 and
103 days respectively in comparison to that of fl ax seedlings grown in inoculated soil with
no added compost (HLT 41 days). Lumsden
et al
. (1983) added composted sewage sludge
to pots of fi eld soils naturally or artifi cially infested with one or more crown or root-rot
pathogens. They found that the addition of composted sewage sludge to soil (10% by
volume) signifi cantly reduced incidence and severity of diseases including:
Aphanomyces
eutiches
on pea,
Rhizoctonia solani
on bean and cotton,
Phytophthora capsici
on pepper,
Sclerotinia minor
on lettuce and
Fusarium oxysporum
f. sp.
melonis
on melons.
It is recognized that the suppressiveness of individual composts used as components
of container media may not be replicated in commercial crops grown in fi eld soils. There
are many examples where workers have found no disease suppression in fi eld soils when
using composts that had previously been shown to suppress disease under laboratory or
glasshouse bioassays. This may be partly because the environment in which host, patho-
gens and benefi cial organisms live is more variable and more diffi cult to control in the
fi eld. However, the large body of information that has built up from container media trials
is already providing useful indications of which composts may help confer suppressive-
ness to fi eld soils.
5.7.2
Field crops
Pathogen suppression in fi eld-grown crops following application of composts is consider-
ably less predictable than that in container media when plants have been produced under
