Integrated pest management, i.e., the combined use of multiple control methods to maintain pest damage below an economic threshold, is one of the fundaments of sustainable agriculture, as choice of pest management tactics specifically addressed to cropping systems and technical conditions optimizes performances of existing tactics and eliminates unnecessary pesticide applications (Mullen et al. 1997; Perrin 1997; Martin 2003). Soil solarization demonstrated a large suitability for integrated pest management strategies, as adaptable to most cropping systems and compatible or synergistic with a large number of chemical, biological, and cultural control methods (Stapleton and DeVay 1995; Katan 2000; Stapleton 2000). General achievement of integrated pest management and need for large spectrum control strategies led a number of researchers to investigate effects and mechanisms of the combination of solarization with almost all the available alternative tactics for the control of soilborne pathogens, nematodes, and weeds.
Integration of solarization with reduced rates of fumigants provided additional suppressive effects on many fungal pathogens, though this improved control was not evident in soils with a long previous fumigation history (Albregts et al. 1996) (see Fig. 9.7). Synergistic application of solarization and methyl bromide, metham sodium, 1,3-dichloropropene + chloropicrin, or dazomet was positively verified for reducing incidence viability and symptoms of V. dahliae, F. oxysporum, and S. rolfsii (Frank et al. 1986; Ben-Yephet et al. 1988; Eshel et al. 2000; Yucel et al. 2007); Rhizoctonia spp., P. cactorum, and P. capsici (Yucel 1995; Benlioglu et al. 2005); P. nicotianae, F. oxysporum, and S. rolfsii (Chellemi et al. 1994, 1997; Stevens et al. 2003; Chellemi and Mirusso 2006); P. lycopersici and P. terrestris (Tjamos 1984; Porter et al. 1989); and P. brassicae (Porter et al. 1991). Sequence of treatments was shown to play an important role in the final result, as Eshel et al.
(2000) found application of field sublethal heating followed by fumigation treatment significantly more effective than the opposite sequence. Moreover, additional soilborne disease agents were found to be controlled by pre-wetting soil with metham sodium before solarization (Frank et al. 1986; Tjosvold 2000). Nematicidal effect of soil solarizing treatment was also found to be enhanced by combination with low doses of fumigant nematicides, such as 1,3-dichloropropene (Stapleton and Devay 1983), ethylene dibromide (Barbercheck and Von Broembsen 1986), methyl bromide (Cartia et al. 1989), metham sodium, or dazomet (Yucel et al. 2007). Combination of soil solarization with reduced dosages of 1,3-dichloropro-pene further reduced populations of root-knot nematodes on tomato and pepper (Capsicum annuum L.) and of G. rostochiensis on potato in USA (LaMondia et al. 1986; Chellemi and Mirusso 2006) and densities of H. carotae on carrot and D. dipsaci on onion in Italy (Greco et al. 1990; Greco et al. 1992). Association of solar heating with granular nematicides also demonstrated to be effective for reducing root galling by M. incognita on lettuce and melon (Lamberti et al. 2000). However, other field experiments in California showed no improved control of M. incognita and C. xenoplax by nematicide-combined solarization (Stapleton et al. 1987). Finally, Peachey et al. (2001) documented an improved solarization suppressive-ness on weeds by the integration with low rates of metham sodium.
Biocidal activity of organic amendments was hypothesized to be originated by a shift of soil microflora toward antagonistic populations and/or by toxic compounds released during organic matter breakdown (Stirling 1988). Synergism of solariza-tion with amendments may be due to the enhancement of these mechanisms, as Gamliel and Stapleton (1997) found a significantly higher concentration of many volatile compounds released from decomposing organic materials into the solarized soil atmosphere.
An effective integration of solarization treatment with a variety of organic amendments, such as composts, crop residues, green manures, and animal manures, was reported for the control of soilborne pathogens (Kodama and Fukui 1982; Freeman and Katan 1988; Gamliel and Stapleton 1993a,b; Chellemi et al. 1997). High-nitrogen organic materials were effective in reducing inoculum densities of various soilborne pathogens, including heat-resistant species like M. phaseolina, and nematodes (Chun and Lockwood 1985; Lodha 1995; Rodriguez-Kabana 1986). Combination of solarization with these materials may be highly effective, as ammonia and/or nitrous acid generated during the decomposition process are retained for longer periods and more effectively diffused in plastic covered soil (DeVay and Katan 1991; Lazarovits et al. 2001; Lodha et al. 2003). Chicken litter amendments were found to improve solarization effect on P. ultimum in lettuce (Gamliel and Stapleton 1993), Rhizoctonia spp. and P. cactorum on strawberry (Benlioglu et al. 2005), and S. rolfsii on tomato (Stevens et al. 2003), and integration with urea or farmyard manure was highly effective in reducing F. oxysporum f. sp. cumini and M. phaseolina (Lodha 1995). Ndiaye et al. (2007) reported a strong reduction of inoculum density of M. phaseolina and charcoal rot symptoms severity on cowpea, Vigna unguiculata (L.) Walpers, by combining solarization with nitrogen-enriched millet residues, whereas no effectiveness was derived from the integration of solar-ization and butchering residues (Kurt and Emir 2004). Combination of soil solariza-tion with various organic amendments (broiler litter, cottonseed meal, feather meal, soybean oilcake, and urban plant debris) also demonstrated to improve root-knot nematode suppression, compared to single treatments alone, under different conditions (Gamliel and Stapleton 1993b; Stevens et al. 2003; Chellemi 2006; Oka et al. 2007). Moreover, Greco et al. (1992) reported an improved suppression of bulb nematode D. dipsaci on onion (A. cepa L.) by solarization of soil previously amended with wheat straw, though combination was ineffective on carrot cyst nematode H. carotae on carrot. Field studies in Lebanon also reported the syner-gism of solarization with chicken manure for weed control, as seed germination of O. crenata and Cuscuta campestris Yunck. was strongly suppressed in amended and then solarized soil (Haidar et al. 1999; Haidar and Sidahmed 2000). Mallek et al. (2007) suggested that amendments with dried crop residues of onion and garlic (Allium sativum L.) may improve weed control of solar heating in unfavorable climate or shorter treatment conditions.
Toxic volatiles, mainly isothiocyanates and aldehydes, released during the degradation of crucifer residues into the soil, were found responsible for the inhibition or reduction of many soilborne pathogens and pests (Angus et al. 1994; Keinath 1996; Mayton et al. 1996; Matthiessen and Kirkegaard 2006). Gamliel et al. (2000) reported that concentration of volatiles was directly related to soil temperature and partial anaerobic conditions occurring under a plastic mulch. The improvement of solarization performances by the combination with brassica-ceous green manure was reported since the early 1980s (Horiuchi et al. 1982), and largely investigated under various experimental conditions throughout the following decades. Association of sublethal heating with crucifer amendments reduced germination of P. ultimum and S. rolfsii under laboratory conditions (Stapleton et al. 1995), and effectively controlled M. phaseolina in field trials (Lodha et al. 2003). Field integration of solarization with brassicaceous amendments was highly effective for the control of F. oxysporum f. sp. conglutinans and M. phaseolina (Ramirez-Villapudua and Munnecke 1987; Ramirez-Villapudua and Munnecke 1988; Souza 1994; Lodha 1995), but also improved suppression of various other soilborne pathogens (Gamliel and Stapleton, 1993a, vb; Gamliel et al. 2000). Incorporation of oil-cakes or green residues of mustard, Brassica juncea (L.) Czern., prior to solarization drastically reduced inocula of F oxysporum f. sp. cucumis and M. phaseolina (Lodha et al. 1997; Lodha and Mawar 2000; Israel et al. 2005), whereas cabbage residues did not enhance solarization effect on soil population of Phytophthora spp. (Coelho et al. 1999). Under greenhouse conditions, solarization integrated with cruciferous biofumigation provided an effective reduction of Pyrenochaeta corky root disease on tomato (Díaz Hernández et al. 2005), and effectively controlled infestation of root-knot nematodes and weeds on melon and pepper (Ploeg and Stapleton 2001; Guerrero et al. 2005). Additive effects could also be obtained from the integrated application of solar-ization and noncruciferous amendments, as Pinkerton et al. (2000) recorded an improved suppression of P. cinnamomi and V. dahliae when solarization was combined with green manures of sudangrass, Sorghum bicolor (L.) Moench subsp. drummondii, and barley (Hordeum vulgare L.), and Flores-Moctezuma et al. (2006) reduced damage of S. rolfsii in onion seedlings by integrating solar heating with green manures of parthenium weed, Parthenium hysterophorus L. Moreover, Lira-Saldivar et al. (2004) documented that leaf resin extract of Larrea tridentata (DC) Coville effectively reduced soilborne pathogens incidence and provided a partial protection against nematodes when combined with solari-zation. Blok et al. (2000) hypothesized the release of toxic compounds as a main mechanism also for the synergistic effect of these noncruciferous green manures in solarized soil.
Inorganic amendments were also reported for an improvement of soil solariza-tion effects (Stapleton et al. 1990). Solarization integrated with calcium cyanamide strongly suppressed or almost completely eliminated population of F. oxysporum and F. solani f. sp. cucurbitae Snyd. and Hans. on a cactus species, Hylocereus trigonus (Haw.) Saff., and cucumber, respectively (Bourbos et al. 1997; Choi et al. 2007). Lower soil densities of phytonematode B. longicaudatus were observed by McSorley and McGovern (2000) by combining solarization with ammonium bicarbonate or ammonium sulfate application.
Integration of solarization with biocontrol agents may represent a further alternative for an improved management of soil pests (Katan 2000). Populations of the antagonistic fungus T. harzianum were found to be not reduced and increase gradually in plant rhizosphere following the heat treatment (Porras et al. 2007a; Jayaraj and Radhakrishnan 2008). Chet et al. (1982) stated that coating iris bulbs with a preparation of T. harzianum was highly effective in reducing incidence of diseases caused by R. solani and S. rolfsii under greenhouse conditions, and integration of solarization with T. harzianum provided a significant control of Fusarium crown and root rot of tomato under field and greenhouse conditions (Yücel and Qinar 1989; Sivan and Chet 1993). Application of T. harzianum strains after soil solariza-tion caused a total loss of inoculum viability of Armillaria spp. (Otieno et al. 2003), or strongly reduced incidence of Pythium damping-off on tomato (Jayaraj and Radhakrishnan 2008). Adversely, combination of soil solarization with T. harzianum did not provide any additive control of R. solani on bean, Phaseolus vulgaris L., P. ultimum on cucumber, and F. oxysporum f. sp. basilici on basil, Ocimum basilicum L. (Minuto et al. 1995). Other biocontrol agents were also demonstrated to improve suppressiveness of solarized soil. Combination of soil solarization with Gliocladium virens Miller, Giddens et Foster proved to be a potential control strategy against S. rolfsii southern blight on tomato and pepper (Ristaino et al. 1991, 1996). Application of fluorescent Pseudomonas strains to solarized soils reduced incidence of R. solani and Pythium spp. diseases in tomato and impatiens (McGovern et al. 2002; Jayaraj and Radhakrishnan 2008), and decreased bacterial wilt caused by R. solanacearum in ginger, Zingiber officinale Roscoe (Anith et al. 2000). Treatments with commercial formulations of Streptomyces spp. improved solarization effectiveness against Pythium spp., R. solani, and Fusarium and Verticillium wilts, whereas variable effects were found on P. lycopersici tomato corky root rot in greenhouse (McGovern et al. 2002; Minuto et al. 2006). Integration of soil solarization with a soil drench of Bacillus subtilis (Ehrenberg) Cohn reduced crown galls caused by A. tumefaciens on cherry rootstock in nurseries (Gupta and Khosla 2007), and use of mixed antagonistic strains of B. subtilis, T. harzianum, and/or Fusarium spp. as seed inoculants reduced the symptoms of R. solani on beet in solarized soil (Gasoni et al. 2007). Biocontrol agents also improved the effect of solar heating on root-knot nematodes, as solarization combined with commercial formulations of plant growth-promoting rhizobacteria or B. firmus Bredemann and Werner was as effective as a chemical treatment for the control of Meloidogyne spp. on tomato and pepper (Kokalis-Burelle et al. 2002; Giannakou et al. 2007). Treatments with a formulation of Pasteuria penetrans after solarization resulted in an additive suppression of M. javanica and M. incognita on cucumber (Tzortzakakis and Gowen 1994), whereas no further nematicidal effect was derived by combining the heat treatment with a commercial formulation of fungus Paecilomyces lilacinus (Thom) Samson (Anastasiadis et al. 2008). Hatcher and Melander (2003) also suggested an integrated use of soil solarization with biocontrol agents for the control of heat-resistant weeds normally escaping heat treatment alone.
Adoption of suitable agronomical practices or a proper soil management may also represent valuable options for an enhancement of solarization effects. Ioannou (2001) reported that use of eggplant seedlings grafted on resistant tomato root-stocks provided a complete protection from Verticillium wilt, corky root rot, and root-knot nematodes in solarized soil. Johnson et al. (2007) documented an effective suppression of C. esculentus to manageable levels by combining a prolonged summer soil solarization with a fallow tillage, and Sotomayor et al. (1999) obtained a successful control of M. arenaria Neal by combination of solarization and soil flooding. Finally, Perrin et al. (1998) suggested that a proper management of myc-
orrhizal symbiosis in solarized soil may provide a valid alternative to soil fumigation, as also demonstrated by the enhanced suppression of pink root disease in chive resulting from AMF symbiosis in solarized soil (Gamliel et al. 2004).
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