- OOMYCETE DISEASES OF CUCURBITS 303
(Gubler and Davis 1996b). Infection of lateral roots and the taproot are
generally observed following irrigations after fruit set.
In greenhouse tests,P. ultimumandP. aphanidermatumcaused plant
collapse when plants that had set fruit were subjected to a brief period
of water stress followed by flooding for a period of 24 or 48 hr. When
plants were maintained fruitless or were not subjected to water stress,
symptoms of sudden wilt did not occur (Gubler and Davis 1996b). In
contrast,P. myriotylumcaused rapid root rot and wilting prior to fruit
set and without water deficit stress.
- Disease Management.Incidence of Pythium damping-off and root
rot can be minimized by planting on raised beds to allow for maxi-
mum water drainage. Planting into raised beds can help avoid water-
logging and promote more rapid germination of seed. Soil temperatures
of 18â21âŚC are favorable for rapid seed germination and seedling emer-
gence and are less favorable for Pythium infection (Gubler and Davis
1996b). Crop rotation with nonhosts (e.g., small grains) may provide
some reduction in damping-off and root rot, butPythiumspecies have
broad host ranges, thus effects of crop rotation may not be significant.
Effects of biocontrol agents on managing Pythium species have
been investigated.Trichoderma harzianum(Lumsden and Locke 1989;
Manoranjitham and Prakasam 2000) andT. hamatum,T. reesei,T. viride,
andPseudomonas fluorescens (Manoranjitham and Prakasam 2000;
Sharma et al. 2014) have been reported effective against Pythium
species, especiallyP. aphanidermatum. Biocontrol agents work best
when pathogen pressure is low to moderate, and are not typically effec-
tive at high pathogen levels. Biocontrol agents are generally most effec-
tive prior to infection (Bardin et al. 2004).
Soil solarization has been used for managing diseases caused by
Pythiumspecies. Soil solarization is a hydrothermal process that occurs
in moist soil when the soil is covered by a plastic film and heated
by exposing to sunlight during the sunny, warm months. The process
changes the physical, chemical, and biological properties of soil and
thereby helps to improve soil health. Under some conditions, it is an
alternative to soil fumigation that may have significant environmental
risks and negative impacts on beneficial soil microorganisms (Pokharel
2010). Efficacy of soil solarization againstPythiumspecies has been
reported by many workers from many vegetable-growing areas (Katan
2000; Mathur et al. 2002; Deadman et al. 2006).
Various organic matters have also been used to manage diseases
caused byPythiumspecies (Kao and Ko 1986; Paulitz and Baker 1987;
Shuler et al. 1989). Organic matter may actuate a chain reaction of