Agriculture Reference
In-Depth Information
controlled conditions. There are examples of disease suppression following application of
composts to fi eld soils, but our understanding of the factors affecting suppression in fi eld
soils is less well developed than that in container production systems. The inconsistency
in the level of disease suppression reported in fi eld soils is probably due to differences in
experimental conditions and in compost types used. Most research in this area focuses on
the three root and soil-borne pathogens
Rhizoctonia, Pythium
and
Phytophthora
spp., but
work also covers other pathogens, including
Colletotrichum, Fusarium, Macrophomina,
Mycosphaerella,
Sclerotinia, Thielaviopsis
and
Verticillium
spp.
A limited number of studies have been carried out in fi eld plots. For example, Bulluck &
Ristaino (2002) examined the effects of composted cotton-gin trash on the incidence of
southern blight of tomatoes (
Sclerotium rolfsii
). Disease incidence was between 3 and
23% in infested plots treated with compost and was between 61 and 67% in infested plots
with no compost. Coventry
et al
. (2006) found that application of onion waste compost
in fi eld studies, reduced the viability of the onion white rot pathogen,
Sclerotium cepivo-
rum
and was as effective in reducing onion white rot as a standard fungicide treatment
(tebuconazole). In a study of the effect of cattle manure composts on the incidence and
severity of black scurf (
Rhizoctonia solani
) on organically grown potatoes, Tsror [Lakhim]
et al
. (2001) found that application of compost at 60 m
3
ha
1
reduced disease incidence
by between 18.6 and 62.3% in comparison to controls with no compost added. Tilston
et al.
(2005) reported that greenwaste compost applied at 100 or 150 t ha
1
ameliorated
the effects of take-all (caused by
Gaeumannomyces graminis
) during a cropping period
with high disease pressure. Finally, Lewis
et al
. (1992) found that amendment of fi eld
plots with composted sewage sludge (7-10 t ha
1
) signifi cantly reduced the incidence of
damping-off of smooth skinned and wrinkled pea cultivars caused mainly by
Rhizoctonia
solani
and
Pythium ultimum
.
It has been shown that composts applied to fi eld soils can also reduce the incidence
and severity of foliar diseases. For example, Weltzein (1990) found that the addition of
composts based on horse manure and straw bedding to soils in pots reduced the incidence
of
Erysiphe graminis
on wheat and barley and
Sphaerotheca fuliginea
on cucumber.
The studies discussed here report differences between disease incidence and/or severity
on untreated soil-grown crops and crops grown in soil which has been treated with
compost. Few comparisons have been made between the level of disease suppression
achieved through the use of composts and that achieved following standard fungicide
treatments. These studies are valid due to the decreasing number of pesticide active
ingredients and to the increasing number of farmers and growers who choose their crops
without pesticides. It is diffi cult to compare different studies, since there is rarely more
than one report of disease suppression using composts for any given crop. The studies
also differ in terms of the feedstocks used, climate, soil type and experimental protocol.
Work to date has, however, covered a range of economically important pathogens and
cropping systems and the results of this work will form a useful platform on which to base
future studies. The variable and often low to moderate levels of disease suppression and
control typically obtained through the use of composts in fi eld soils suggest that the most
important applications for composts would lie in sustainable and organic agriculture and
horticulture, where pesticide use is minimal or absent.
There are considerably more reports of disease suppression following application of
true composts as opposed to stacked or fresh manures (stacked manures are sometimes
