Agriculture Reference
In-Depth Information
10.5.3
Combining solarization with biocontrol agents
Combining biological control agents, as mentioned above (Stevens
et al.,
2003), or other
benefi cial organisms with solarization is an especially attractive approach. Its effective-
ness has been studied with
T.
harzianum
combined with solarization for the control of
Fusarium crown and root rot of tomato (Sivan & Chet, 1993) and of
Rhizoctonia
(Elad
et al.,
1980; Chet
et al.,
1982), and with
Gliocladium
virens
combined with solarization
for controlling
S. rolfsii
(Ristaino
et al.,
1991). Solarization controlled
Armillaria
borne
in coarse plant material and improved control was obtained when it was combined with
application of
T. harzianum
(Otieno
et al.,
2003).
Recently, solarization has been reported as a promising alternative for fi eld-grown cut
fl owers in the US (McSorley
et al
., 2006), when integrated with other measures such as
biorational fungicides and biocontrol agents; for strawberries in Spain when combined
with
Trichoderma
(Porras
et al.,
2007), and for peppers in the US when combined with
cover crops (Wang
et al.,
2006). Combining SH with the biocontrol agent
Streptomyces
griseovirides
was highly effective in controlling soil-borne pathogens in tomatoes (Minuto
et al.,
2006).
10.6
Modelling of soil solarization and
decision-making tools
Modelling
10.6.1
A main diffi culty with SH is its dependence on climate. Thus, there is a need to be able to
predict the effectiveness of solarization in various climatic regions and seasons. This can
be achieved experimentally, by following soil temperatures and pathogen mortality in the
solarized soil, and by modeling.
A variety of models for predicting temperatures of solarized soils under various climatic
conditions have been developed and validated. The fi rst models were developed for arid
conditions (Mahrer, 1979, 1991; Mahrer & Katan, 1981). Simplifi ed models (Cenis,
1989) and a model which is also suitable for more humid areas (Wu
et al.,
1996) were
also developed. However, information on soil temperature in the solarized soil, although
necessary and very helpful, is not suffi cient for predicting the effectiveness of SH for
pathogen control, since it does not take into consideration pathogen mortality that is not
due to heat, as detailed in the section on mechanisms of pest control. Modelling pathogen
control by solarization is usually based on studies of thermal inactivation of pathogens,
utilizing data collected under constant elevated temperatures. Based on chemical reaction
kinetics at constant temperatures, an exponential inactivation relationship is typically
expected (Toledo, 1999). Traditionally, thermal inactivation of microorganisms is con-
sidered a fi rst-order reaction, characterized by a logarithmic change in the organism's
population with time. A logarithmic relationship was indeed found between time and
temperature (at constant temperatures) for the thermal inactivation of four soil-borne
plant pathogens (Pullman
et al.,
1981). Studies on thermal inactivation under fl uctuating
temperatures, such as those naturally prevailing in the fi eld, are much more complicated
to perform, because the partial effects of varying temperatures on pathogens are diffi cult
to weigh, and they require numerical integration to account for their complexity (Shlevin
et al.,
2003). There are other approaches to simulating and modelling pathogen control
