Diseases and Management of Crops under Protected Cultivation

(Diseases and Management of Crops under Protected Cultivation)
PGPR, and other beneficial microorganisms. The effect of soil solarization on earthworms
population has not received much attention but it is thought that they retreat to lower depths to
escape the effect of soil heating. The increased growth response of plants in solarized soil is a well
documented phenomenon and has been verified both in green house experiments and under field
conditions (Broadbent et al, 1977; Katan, 1987; Chen et al., 1991; Singh, 2008).
Combining solarization with other methods
Despite the successes achieved with solarization when used singly this method may be
usefully aided by combination with other methods of disinfestation. As soil solarization is
dependent upon local climatic conditions, sometimes even during conducive periods of the year,
local weather conditions will not permit an effective solarization treatment. Therefore, we must
come up with integrated uses of solarization in order to increase the predictability of the treatment
and thus make it more acceptable to growers. Combining solarization with pesticides, organic
amendments, or biocontrol agents improves disease control. Whenever a pathogen is weakened
by heating, even reduced dosages might suffice for improved control combining with biocontrol
agents, organic amendments, etc.
Low application rates of fungicides, fumigants or herbicides have been successfully
combined with soil solarization to achieve better pest control (Hartz et al, 1993).Simultaneous
application of chemicals and tarping the soil for solarization has been shown to increase the
effectiveness of both the methods because of synergism (Ben –Yephet et al. 1988; Tjamos, 1984).
Reduced doses of metham-sodium (12.5 or 25 ml/m 2 ) applied singly or in combination with soil
solarization synergistically destroyed V. dahliae and F. oxysporum f.sp. vasinfectum in a naturally
infected cotton field. The synergism was attributed to the weakening effect induced by increased
soil temperatures along with the toxicity of the chemical. The combination also reduced to one
week the time needed to kill sclerotia of Sclerotinia sclerotiorum in the top 10 cm of soil in a lettuce
field and reduced apothecia production. Carbendazim has shown slower degradation rates after
solarization, possibly because of changes in the populations of soil microorganisms after
solarization.
Solarization may also be combined with application of crop residues, green and farm yard
manures. There is increasing evidence that these materials release volatile compounds in the soil
that kill pests and help stimulate the growth of beneficial soil organisms (Deadman et al, 2006;
Gamliel and Stapleton, 1993).
Soil solarization has also been successfully combined with biological control. The use of
Trichoderma harzianum with solarization in fields infested with Rhizoctonia solani has been shown
to improve disease control while delaying the buildup of inoculum (Chet et al, 1982). Greenberger
et al, 1987 concluded that solarized soils are frequently more suppressive and less conducive to
certain soil borne pathogens than non-solarized soils. An increase in population of green
fluorescent pseudomonads along with an increase of Penicillium and Aspergillus spp. following
- 40 -