Agriculture Reference
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soil moisture conditions. However, Sanogo (2006) could fi nd no evidence that soil water
saturation predisposed pepper to infection by P. capsici.
Appropriate treatment of irrigation water can be used to reduce pathogen inoculum,
thereby reducing spread of the pathogen. Phytophthora root rot is a problem in container-
grown hardy nursery stock and the pathogen can be spread by irrigation water. In some
recent work, Pettitt et al. (2007) examined the effi cacy of a non-woven capillary matting
fabric (Tex-R ® Pro), coated with a latex polymer-based formulation of cupric hydroxide
(Spin Out ® ), in controlling Phytophthora root rot in container-grown Chamaecyparis
lawsoniana. The fabric was used as bed covers and was also cut into discs which were
used to cover the tops of the plant containers or were inserted to cover the holes at the
bottoms of the containers. Bed covers and disc inserts were found to signifi cantly reduce
disease spread, while pot toppers were not effective. In addition to reducing spread of the
pathogen in irrigation water, survival of zoospores and zoospore cysts was also signifi -
cantly reduced by this fabric (Pettitt et al., 2007).
2.4.5
Flooding
Flooding can be used in crop protection, since it reduces weeds as well as numbers
of fungal propagules, nematodes and insects in the soil. However, fl ooding can also
spread pathogens and indeed, its success in disease management is variable, depend-
ing on the pathogens present in the soil. Thus, Teo et al. (1989) found that 65% of
sclerotia of S. sclerotiorum were destroyed after two years in the fi eld at high moisture
(5.9-26.2%) compared with 45% at low soil moisture (0.0-1.7%). As a result, they
concluded that incorporating an appropriate irrigation schedule into the crop rotation
system might reduce inoculum of S. sclerotiorum (Teo et al., 1989). Unfortunately,
frequent irrigation could increase alternaria blackspot and root rot (Teo et al., 1988;
Saharan, 1992). Interestingly, in a study of the population dynamics of M. cannonbal-
lus, Beltran et al. (2005) found that although ascospore numbers declined in fi elds
that were in fallow and fl ooded for three years, soil-borne inoculum was viable and
capable of infecting muskmelon. Clearly, M. cannonballus is well adapted to sur-
vive in soils which maintain a high water table or under fl ooding (Beltran et al.,
2005). Eradication of some pathogens can be achieved effectively with fl ooding, but
it is expensive, adversely affects soil structure and its effect in controlling disease is
temporary (Kharbanda & Tewari, 1996).
2.5
A range of root-inhabiting pathogens, for example, Pythium spp., some Phytophthora spp.
and some Fusarium spp., survive saprophytically on soil organic matter or exist for long
periods in the soil in the absence of the host plant, making them diffi cult to control.
Interestingly, some soils have the capacity to suppress such pathogens, with the result
that crops grown in such soils exhibit less disease, even if other environmental conditions
are favourable (van Bruggen, 1995). Baker & Cook (1974) described suppressive soils as
those in which disease severity or incidence remains low, despite the presence of a patho-
gen, a susceptible host plant, and environmental conditions favouring pathogen infection
and subsequent disease development. Soil suppressiveness can be the result of different
Suppressive soils
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