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4. Effect of soil solarization on fungi and bacteria
Use of soil solarization for control of fungal
and bacterial plant pathogens including biocontrol
Control of verticillium wilt and fusarium wilt
diseases by soil solarization in Southern Spain
Control of fusarium solani broad
bean by solar heating of the soil in Northern Iraq
The use of solar energy for controlling white
rot disease of garlic
Use of soil solarization for control of fungal and bacterial plant pathogens including biocontrol
James E. DeVay, Department of Plant Pathology, University of California, Davis, CA 95616 USA
Disinfestation of soil of soilborne pathogens and pests has been mainly based on methods of soil fumigation and soil steaming (3, 13), although soil flooding for various periods also has been effective (41). However, the report of Katan et al. (28) in 1976 on the use of solar heating for disinfesting soil of pathogens and pests, now known as soil solarization, attracted the attention of many agriculturalists and is now widely used (29). In contrast to soil steaming or chemical fumigation of soil, which are broad spectrum in their killing action of soilborne organisms (3, 13), soil solarization is non-chemical, is selective in its action, and improves the filth and nutrient status of soil (26, 51). Temperatures associated with soil steaming usually exceed the maximum temperatures (60° to 61.5°C) that can be tolerated by eucaryotic organisms and some non-spore-forming bacteria, although for some bacteria, life-limiting temperatures are over 100°C. (9).
The application of chemical fumigants to soil for plant disease control has a long history dating back to 1869, and for soil steaming, back to 1893 (3). However, the near-sterilization of agricultural soils by soil steaming or fumigation is now viewed with concern since these procedures destroy many of the beneficial and essential biotic and abiotic elements of soil, including biological control of plant pathogens, which are necessary for plant health (3, 13). In this sense, soil solarization is an important advance because it targets mesophylic organisms, which include most plant pathogens and pests, without destroying the beneficial mycorrhizal fungi and the growth-promoting Bacillus spp. (51, 43, 50); it contributes significantly to the principles of sustainable agriculture (36). Moreover, the increasing constraints of public opinion and regulations regarding chemical pollution of the environment by pesticides and the danger associated with their use, have focused attention on alternative methods for pest control, such as soil solarization and biological controls.
Technology of Soil Solarization
Soil solarization is a mulching process and is an extension of current mulching practices of using plastic films to warm soils to increase seed germination and seedling growth during cool weather or in the early spring months. The distinction, however, between soil solarization and the use of plastic films for warming soils, is that soil solarization reaches killing temperatures for many soilborne organisms, including pathogens, seeds, and weed seedlings. Soil solarization has been especially useful in regions with high solar radiation and where daily temperatures reach 32°C or higher, it is non-chemical, easily applied and is of no danger to workers; it encompasses the objectives of integrated pest management (IPM) (36) and reduces the use of toxic chemicals for plant disease and pest control.
Soil Preparation. The soil in field or glasshouse areas to be solarized should be prepared to provide a smooth surface so that the plastic film will lie flat. The presence of large clods of soil or plant debris that raise the plastic film from the soil will cause air pockets which insulate the soil and reduce the rise in temperature needed for effective solarization. Also, laying the plastic film across deep furrows will reduce the effectiveness of soil solarization, especially in the furrows.
Soil can be prepared for solarization with or without raised planting beds. For raised beds, the plastic film is laid over the length of the bed and the edges are buried in the furrows. For crops grown without beds or on-the-flat, the edges of the plastic are anchored or buried in the soil about 20 cm deep. For large scale use of solarization on-the-flat, the plastic sheets can be glued together or folded together and buried in soil in such a way as to connect the plastic sheets in a continuous layer of film.
Soil Moisture. Soil solarization is a hydrothermal process and its success depends on moisture for maximum heat transfer to soilborne organisms. It has been shown that the temperature maxima of soils increase with increasing moisture content (32). Soil should be at least 70 percent of field capacity in the upper zones and moist to depths of at least 60 cm. If the field or soil area is level, irrigation under the plastic film can be accomplished by running water down shallow furrows made by tractor wheels. However, pre-irrigation of soil may be more practical, especially for uneven areas or fields; the plastic film should be laid within a few days or as soon as the soil will support machinery without compaction. When soil is bedded-up before solarization, the plastic film is laid over the bed and anchored on each side in the furrows. Irrigation water is then run in the furrows and the moisture will be absorbed into the raised beds.
Postplant solarization in newly planted or established orchards or vineyards has shown that soil under the canopy of perennial or woody plants can be effectively solarized without heat injury to the plants (2, 48, 58). Plastic polyethylene (PE) film up to 4 metres square is cut to the centre in order to place the film around the base of the tree. Plastic tape is then used to seal the PE around the trunk of the trees or vines and also to seal the cut edges together. The outside edges of the PE are anchored in the soil. In postplant solarization it is convenient to irrigate the soil before applying the PE film. After an initial pre-irrigation or irrigation under the PE film, no further irrigation is necessary since the soil will remain moist for several months. In semi-arid regions, postplant solarization of soil around fruit trees has greatly reduced the amount of water needed for irrigation (48, 52).
Plastic Films. Polyethylene, polyvinylchloride, and ethlyene vinyl acetate are plastic films most frequently used for soil solarization. Among these, transparent polyethylene (PE) is ideal for soil solarization because it is transparent to solar radiation (280 to 2 500 nm) except for two narrow bands in the far infra-red; it is much less transparent to terrestrial radiation (5 000 to 35 000 nary), reducing the escape of heat from the soil. Additionally, PE films are flexible and have high tensile strength and resist puncturing and tearing. Without ultra-violet stablizers in the plastic, PE films may deteriorate within four to six weeks, although fresh film (1 or 2 mil in thickness) has lasted as long as nine weeks under field conditions without major deterioration (43). In several studies, the thinner transparent PE films (I to 1.5 mil) have been more effective in solar heating of soil than thicker films (2 to 6 mil) or black PE film (26, 43, 51). Using a double layer of plastic creates an inner layer of air which acts as an insulator and the soil heats several degrees higher than soil being solarized with a single layer of plastic film (6, 10). A similar principle is evident when glasshouse soils are solarized (17, 21).
Soil Temperature. The heating of soil during solarization is dependent on several factors, such as soil moisture content, the duration and intensity of sunlight, air temperature, the thickness and transparency of plastic to solar radiation and to terrestrial radiation. The colour of soil is also important; dark soils reach higher temperatures during solar radiation than lighter coloured soils due to their greater absorption of solar radiation. Of major importance for effective soil solarization is the preparation of the soil surface so that the plastic film lies flat against the soil and is not raised up by clods and plant debris, following the line of deep furrows. Depending on soil depth, maximum temperatures of solarized soil in field areas are commonly between 42° to 55°C at the 5 cm depth and range from 32° to 36°C at the 45 cm depth. Solarized soil under glasshouse conditions or under double layers of transparent PE film, reaches higher temperatures than soil under a single layer of film in the field (10, 21).
Effects of Soil Solarization on Soilborne Organisms
The decline in the viability of soilborne micro-organisms and weed seeds during solarization depends on both the soil temperature and exposure time, which are inversely related. For example, the ED90 of Verticillium dahliae at 37°C in soil with moisture at field capacity was about 14 hours whereas at 50°C it was approximately 9 minutes (42). Similar time/temperature relationships hold for most plant pathogenic micro-organisms which are grouped as mesophiles. However, some plant pathogenic fungi, such as Macrophomina phaseolina and Pythium aphanidermatum are less heat sensitive than most other soilborne plant pathogens (8); their control requires optimal conditions of temperature and moisture during solarization (33, 46, 52).
Sensitivity to High Soil Temperatures. Various lines of evidence have been reported regarding the ability of micro-organisms to withstand high temperatures (54); however, the older concept that a high turnover of macromolecules is the basis for thermos/ability is no longer accepted (54). All macromolecules of thermophilic organisms that survive at temperatures up to 60 C appear to be stable at these high temperatures (54).
Direct Effects of Soil Solarization. The inability of organisms to tolerate high temperatures is related to an upper limit in the degree of fluidity of membranes, beyond which breakdown of membrane function may be associated with membrane instability (54). Additional causes for the thermal decline of microorganisms at high temperatures involve the sustained inactivation of respiratory enzymes (9, 54). These are direct affects of high soil temperatures and account for a major share of the reduction in populations of soilborne micro-organisms and weed seeds.
Indirect Effects of Soil Solarization. Some effects of soil solarization are indirect. For example, cells of plant pathogens weakened by heat stress are more vulnerable by several orders of magnitude to soil fumigants, to antagonistic micro-organisms which are more able to tolerate high soil temperatures, and to changes in the gas environment which may develop during soil solarization.
During solarization of soil, changes occur in the structure or filth of soil, in soluble mineral substances available for plant and microbial growth, and in the populations of soilborne micro-organisms (11, 50, 53). These changes effect the inoculum density of plant pathogens, and also their aggressiveness and survival. Changes in the populations of other soilborne micro-oganisms occur during and after solarization which may influence the disease suppressiveness of soil and also the increased plant growth response associated with solarized soils (26, 50, 53).
Effects of Solarization on Soilborne Bacteria
During solarization of soil, populations of oxidaze negative fluorescent pseudomonads and gram positive bacteria, including Bacillus species, may be reduced by 78 to 86 percent compared with non-solarized soil (50); whereas, populations of Actinomycetes may be reduced from 45 to 58 percent in solarized soil (50). Surprisingly, after solarization, Pseudomonas species quickly recolonize the soil and their populations reach high levels (16). Of great significance is the change in populations of Bacillus species during solarization; the percentage of colonies in solarized soil which exhibited antibiosis to Geotrichum candidum increased nearly 20-fold when compared with non-solarized soil (50). These bacteria are among those which are rhizosphere competent and are believed to contribute to the increased growth response of plants grown in solarized soil (26, 50). Although initial populations of Bacillus species are greatly reduced, they are spore formers and are a major component of the soil microflora.
In contrast to the studies in California (50) and Israel (16), studies in Western Australia (22) showed that solarization increased the total numbers of bacteria and actinomycetes in soil. However, as in the California study (50) where there was an increase in the proportion of antagonistic gram positive bacteria in solarized soil, the Western Australia study (22) showed that the proportion of bacteria (actinomycetes) antagonistic to Fusarium oxysporum, F. solani, and Rhizoctonia solani was increased compared with non-solarized soil. In other studies (12), Actinomyces scabies was controlled by soil solarization.
Only limited studies have been made on the survival of plant pathogenic bacteria in solarized soil; however, Agrobacterium species are highly sensitive to solarization and populations are reduced up to 72 percent (50). Similarly, species of Rhizobium are heat sensitive and their populations are greatly reduced during soil solarization(1, 26). Since none of the plant pathogenic bacteria form spores, their decline in solarized soil is expected to parallel that of green fluorescent pseudomonads (50). However, pseudomonads are among the bacteria that quickly recolonize solarized soil and reach high populations (16, 26, 49, 51); some are rhizosphere competent and can provide a degree of protection against fungal root pathogens and stimulate plant growth (15, 18, 24, 25, 26, 30, 50). Like the pseudomonads, some strains of Bacillus species are rhizosphere competent and either through aggressive growth or the production of antibiotics, they appear to be major contributors to the disease suppressiveness of soils following solarization (26, 50). Bacillus species are the predominant Gram-positive bacteria that survive soil solarization (49). Recolonization of solarized soils includes saprophytic bacteria which have less stringent nutritional requirements than plant pathogens (34).
Effects of Solarization on Soilborne Fungi
Plant pathogenic fungi are among the most sensitive soilborne organisms to soil solarization, especially species that are unable to grow at temperatures higher than 30° to 33°C; they are categorized as mesophiles. Immediately after soil solarization, the population densities of "total" fungi were reduced by 85 to 90 percent in different experimental plots. However, population densities of thermotolerant and thermophilic fungi remained relatively high following solarization, and increased to levels higher than present in non-solarized soil (49). The fungi most frequently isolated were thermotolerant Aspergillus and Penicillium species (49).
In regard to the effect of soil solarization on beneficial soilborne microorganisms, the mycorrhizal fungus Glomus fasiculatus survives solar heating of soil to the extent that there does not appear to be a reduction in its colonization of host roots in solarized soil (43, 53).
Many plant pathogenic fungi, with the exception of Macrophomina phasseolina, Pythium aphanidermatum, and species of Aspergillus, Penicillum and Glomus. are differentially sensitive to moist heat and have been controlled by soil solarization. Depending on numerous variables in climate, soil conditions, populations and distribution of fungal propagules in soil, and technological differences in the use of soil solarization, different workers have been more or less successful in controlling plant pathogens and pests. A partial list of the fungal pathogens controlled by soil solarization is given in Table 1.
Weakening of Fungal Propagules and Biological Control
Soilborne propagules of fungi that are subjected to sublethal heat effects during solarization appear to have an increased sensitivity to antagonistic fungi and to bacteria which are less affected by soil solarization; the weakened propagules are also more sensitive to soil fumigants and other pesticides (15, 18, 24, 25, 30, 42). Sublethal temperatures also may cause delays in germination of propagules and reduced virulence in host plants, that vary with temperature and the duration of exposure. Working with Pythium ultimum, Rhizoctonia solanai, V. dahliae, and Thielaviopsis basicola, Pullman et al. (42) found that these effects of sublethal temperatures were most pronounced when the fungi were exposed to temperatures of 37° to 39°C. The longer a propagule was exposed to sublethal heating, the longer was the time required for germination. They (42) suggested that this relationship indicates that heat damage accumulates gradually to a point beyond which the propagule cannot recover.
During sublethal heating, all living cells produce heat shock proteins (14, 31, 38, 39). Heat shock proteins are associated with the acquistion of thermotolerance or thermos/ability; however, fungi have a transient heat shock response that is shortlived, even if they are maintained at high temperature (38). The overall effect of heat shock proteins on the survival of fungi during soil solarization is unknown.
Other effects of sublethal heating are well documented, especially in the case of Sclerotium rolfsii where the rind of sclerotia becomes cracked resulting in increased leakage of various substances (30). Weakened sclerotia are intensely colonized by Trichoderma harzianum and other micro-organisms (18, 30). Another example where soil solarization may affect the germinability and aggressiveness of fungal propagules concerns Rosellinia necratrix. Postplant solarization of an apple orchard for the control of this pathogen provided evidence that the fungal propagules became highly vulnerable to colonization by Trichoderma species (56).
Suppressiveness of Soil after Solarization
The benefits of soil solarization involving pathogen and pest control and an increased growth response of crop plants commonly last for about two growing seasons (19, 26, 27, 51, 58, 59). Among micro-organisms which survive the solarization process and contribute to the suppressiveness of soil, the predominant bacteria are Bacillus species (50) whereas Trichoderma species and Talaromyces flavus are representative of the main fungal antagonists which inhibit the development of pathogenic fungi (58, 22, 26). Long-term effects of soil solarization have been observed for control of Verticillium and Fusarium wilts of cotton in Israel and in California (27,33), and for corky root of tomatoes and pink root and white rot of onion (1).
The development of disease suppressiveness in solarized soil reflects the recolonization of the soil by aggressive mycoparasites, which are also rhizosphere competent. Microbial antagonists, such as Bacillus species, are also associated with the increased growth response of plants growing in solarized soil (50).
Enhancing the Effectiveness of Soil Solarization
Using soil solarization in combination with soil fumigants or with certain crop residues (5, 44) greatly shortens the lime needed to control pathogens and pests and extends the use of solarization to regions which are considered marginal because of air temperatures, length of day, and intensity of sunlight. For example, the combined action of metham-sodium (methylisothioc-yanate) and soil solarization was much more effective than either soil treatment used singly for control of V. dahliae and Fusarium oxysporum f. sp. vasinfectum (5). Whereas metham-sodium reduced the viability of propagules of V. dahliae to 30 percent of the control in one week and soil solarization alone reduced the count to 18 percent after six weeks, the combination of the two treatments begun in July, reduced the number of detectable propagules to 0 within one week (5). Additionally, when the comparisons were begun in August (lower air temperatures and shorter days), solarization or metham-sodium alone had little or no effect on the viability of propagules of V. dahliae after six weeks: however, solarization combined with metham-sodium reduced the viability of the propagules to 26 percent of the control after two weeks and to I percent after 6 weeks (5).
In other studies, amending field soils with dry cabbage (Brassica oleracea) leaves before soil solarization, resulted in a significantly larger decrease in both cabbage yellows and delectable propagules of F. oxysporum f. sp. conglutinans when compared with either solarization or cabbage leaves alone (44).
Conclusions
Soil solarization is a useful alternative in many places for the disinfestation of soil for the control of numerous and diverse fungi and bacteria and various crop pests. Depending on several variables, soil solarization has met with great success in some situations and failure in others for managing plant diseases and pests. With greater understanding of the components of soil solarization and their interaction, the uses of this alternative for chemical or steam treatments for disinfesting soil should increase.
References
1. Abdel-Rahim, M. F., M. M. Satour, K. Y. Mickail, S. A. El-Eraki, A. Grinstein, Y. Chen, and J. Katan. 1988. Effectiveness of soil solarization in furrow-irrigated soils. Plant Dis. 72:143-146.
2. Ashworth, L. l. and S. A. Gaona. 1982. Evaluation of clear polyethylene mulch for controlling Verticillium wilt in established pistachio nut groves. Phytopathol. 72:243-246.
3. Baker, K. F. and R. J. Cook. 1974. Biological Control of Plant Pathogens. Freeman, San Francisco. 433 pp.
4. Barbercheck, M. E. and S. L. von Broembsen. 1986. Effects of soil solarization on plant parasitic nematodes and Phytophthora cinnamomi. Plant Dis. 70:945-950.
5. Ben-Yephet, Y., J. M. Melero-Vara, and J. E. DeVay. 1988. Interaction of soil solarization and metham-sodium in the destruction of Verticillium dahliae and Fusarium oxysporum f. sp. vasinfectum. Crop Protect. 7:327331.
6. Ben-Yephet, Y., J. J. Stapleton, R. J. Wakeman, and J. E. DeVay. 1987. Comparative effects of soil solarization with single and double layers of polyethylene film on survival of Fusarium oxysporum f. sp. vasinfectum. Phytoparasitica 15:181-185.
7. Besri, M. 1983. Solar heating (solarization) of tomato supports for control of Didimella Iycopersici stem canker. Phytopath. Z. 108:333-340.
8. Bollen, G. J. 1985. Lethal temperatures of soil fungi. p. 191 In: Ecology and Management of Soilborne Plant Pathogens. Proc. Fourth Inter. Congress of Plant Pathol. Parker, C. A., Rovira, A. D., Moore, K. J., and Wong, P. T. W., Eds. The American Phytopathological Society, St. Paul.
9. Brock, T. D. 1978. ThermophyIic Microorganisms and Life at High Temperatures. Springer-Verlag, New York. 465 pp.
10. Cenis, J. L. 1987. Double plastic sheet for improving soil solarization efficiency. In: Proc.7th Congress of the Mediterranean Phytopathological Union (Spain). p. 73.
11. Chen, Y. and 1. Katan. 1980. Effect of solar heating of soils by transparent polyethylene mulching on their chemical properties. Soil Sci. 130:271-277.
12. Davis, J. R. and L. H. Sorensen. 19X6. Influence of soil solarization at moderate temperatures on potato genotypes with differing resistance to Verticillium dahliae. Phytopathol. 76:1021-1026.
13. Dawson, J. R., R. A. Johnson, P. Adams, and F. T. Last 1965. Influence of steam/air mixtures, when used for heating soil, on biological and chemical properties that affect seedling growth. Ann. Appl. Biol. 56:24351.
14. Freeman, S., C. Ginzburg, and J. Katan. 1989. Heat shock protein synthesis in propagules of Fusarium oxysporum f. sp. niveum. Phytopathol. 79: 1054- 1059.
15. Freeman, S. and J. Katan. 1988. Weakening effect on propagules of Fusarium by sublethal heating. Phytopathol. 78:1656-1661.
16. Gamliel, A., E. Hadar, and J. Katan. 1987. Microbial phenomena related to increased growth response in solarized soils and to monoculture systems. p. 72. In: Proc. 7th Congress of the Mediter. Phytopathol. Union (Spain).
17. Garibaldi, A. and G. Tamietti. 1984. Attempts to use soil solarization in closed glasshouses in northern Italy for controlling corky root of tomato. Acta Hort. 152:237-243.
18. Greenberger, A., A. Yogev, and J. Katan. 1984. Biological control in solarized soils. Proc. Sixth Congress of the Mediter. Phytopathol. Union (Cairo), p. 112-114. (Abstract).
19. Greenberger, A., A. Yogev, and J. Katan. 1987. Induced suppressiveness in solarized soils. Phytopathol. 77:1663-1667.
20. Grinstein, A., J. Katan, A. Abdul-Razik, O. Zeidan, and Y. Elad. 1979. Control of Sclerotium rolfsii and weeds in peanuts by solar heating of soil. Plant Dis. Reptr. 63:1056-1059.
21. Horiuchi, S. 1984. Soil solarization for suppressing soilborne diseases in Japan. p. 11-23. In: The Ecology and Treatment of Soilborne Diseases in Asia. Food and Fertilizer Technology Center Tech. Bull. 78. Taiwan,R.O.C.
22. Kaewruang, W., K. Sivasithamparam, and G. E. Hardy. 1989. Use of soil solarization to control root rots in gerberas (Gerbera jamesonii). Biol. Fert. Soils 8:38-47.
23. Kassaby, F. Y. 1985. Solar-heating soil for control of damping-off diseases. Soil Biol. Biochem. 17:429-434.
24. Katan, J. 1984. Soil solarization. Acta Hort. 152:227-236.
25. Katan, J. 1985. Solar disinfestation of soils, Proc. Fourth Inter. Congress of Plant Pathol. p. 274. Parker, C. A., A. D. Rovira, K. J. Moore, and P. T. W. Wong, Eds. The Amer. Phytopathol. Soc., St. Paul.
26. Katan, J. 1987. Soil solarization. p. 77-105. In: Innovative Approaches to Plant Disease Control. 1. Chet, Ed. John Wiley & Sons, New York.
27. Katan, J., G. Fishler, and A. Grinstein. 1983. Short- and long-term effects of soil solarization and crop sequence on Fusarium wilt and yield of cotton in Israel. Phytopathol. 73:1215-1219.
28. Katan, J., A. Greenberger, H. Alon, and A. Grinstein. 1976. Solar heating by polyethylene mulching for the control of diseases cuased by soilborne pathogens. Phytopathol. 66:683-688.
29. Katan, J., A. Grinstein, A. Greenberger, O. Yarden, and J. E. DeVay. 1987. The first decade (1976-1986) of soil solarization (solar heating): a chronological bibliography. Phytoparasitica 15:229-255.
30. Lifshitz, R., M. Tabachnik, J. Katan, and I. Chet. 1983. The effect of sublethal heating on sclerotia of Sclerotium rolfsii. Can. J. Microbiol. 29:1607-1610.
31. Lindquist, S. 1986. The heat shock response. Annual Review of Biochem. 55:1151-1191.
32. Mahrer, Y., O. Naot, E. Rawitz, and J. Katan. 1984. Temperature and moisture regimes in soils mulched with transparent polyethylene. Soil Sci. Soc. Amer. 1. 48:362-367.
33. Mihail, J. D. and S. M. Alcorn. 1984. Effects of soil solarization on Macrophomina phaseolina and Sclerotium rolfsii. Plant Dis. 68:156159.
34. Misaghi, I. and R. G. Grogan. Nutritional and biochemical comparisons of plant-pathogenic and saprophytic fluorescent pseudomonads. Phytopathol. 59:1436-1450.
35. Myers, D. F., R. N. Campbell, and A. S. Greathead. 1983. Thermal inactivation of Plasmodiophora brassicae Woron. and its attempted control by solarization in the Salinas Valley of California. Crop Protect. 2:325-333.
36. Paul, E. A. and G. P. Robertson. 1989. Ecology and the Agricultural Sciences: A false dichotomy? Ecology 70:1594-1597.
37. Pinkas, Y., A. Kariv, and J. Katan. 1984. Soil solarization for the control of Phytophthora cinnamomi thermal and biological effects. Phytopathol. 74:796 (Abstract).
38. Plesofsky-vig, N. and R. Brambl. 1985. Heat shock response of Neurospora crassa: protein synthesis and induced thermotolerance. J. Bacteriol. 162:1083-1091.
39. Plesofsky-vig, N. and R. Brambl. 1985. The heat shock response of fungi. Exper. Mycol. 9:187-194.
40. Porter, I. J. and P. R. Merriman. 1985. Evaluation of soil solarization. for control of root diseases of row crops in Victoria. Plant Pathol. 34:108118.
41. Pullman, G. S. and J. E. DeVay. 1982. Effect of soil flooding and paddy rice culture on the survival of Verticillium dahliae and incidence of Verticillium wilt in cotton. Phytopathol. 72:1285-1289.
42. Pullman, G. S., J. E. DeVay, and R. H. Garber. 1981. Soil solarization. and thermal death: a logarithmic relationship between time and temperature for four soilborne plant pathogens. Phytopathol. 71:959-964.
43. Pullman, G. S., I. E. DeVay, R. H. Garber, and A. R. Weinhold. 1981. Effects on Verticillium wilt of cotton and soilborne populations of Verticillium dahliae, Pythium spp., Rhizoctonia solani, and Thielaviopsis basicola. Phytopathol. 71:954-959.
44. Ramirez-Villapudua, J. and D. E. Munnecke. 1987. Control of cabbage yellows (Fusarium oxysporum f. sp. conglutinans) by solar heating of field soils amended with dry cabbage residues. Plant Dis. 71:217-221.
45. St. J. Hardy, G. E. and K. Sivasithamparam. 1985. Soil solarization: Effects on Fusarium wilt of carnation and Verticillium wilt of eggplant. p. 279 Proc. Fourth International Congress of Plant Pathology. C. A. Parker, A. D. Rovira, K. J. Moore, and P. T. W. Wong, Eds., The American Phytopathological Society, St. Paul, MN.
46. Sheikh, A. H. and A. Ghaffar. 1987. Time-temperature relationships for the inactivation of sclerotia of Macrophomina phaseolina. Soil Biol. and Biochem. 19:313-315.
47. Smith, E. M., F. C. Wehner, and J. M. Katze. 1984. Effect of soil solarization and fungicide soil drenches on crater disease of wheat. Plant Dis. 68:582-584.
48. Stapleton, J. J., W. K. Asai, and J. E. DeVay. 1989. Use of polymer mulches in integrated pest management programs for establishment of perennial fruit crops. Acta Hort. 255:161-1267.
49. Stapleton, J. J. and J. E. DeVay. 1982. Effect of soil solarization on populations of selected soilborne microorganisms and growth of deciduous fruit tree seedlings. Phytopathol. 72:323-326.
50. Stapleton, J. J. and J. E. DeVay. 1984. Thermal components of soil solarization as related to changes in soil and root microflora and increased growth response. Phytopathol. 74:255-259.
51. Stapleton, J. J. and J. E. DeVay. 1986. Soil solarization: a non-chemical approach for management of plant pathogens and pests. Crop Protection 5: 190-198.
52. Stapleton, J. J. and J. G. Garcia-Lopez. 1988. Mulching of soils with transparent solarization. and black polyethylene films to increase growth of annual and perennial crops in southwestern Mexico. Trop. Agric. 65:29-33.
53. Stapleton, J. J., J. Quick, and J. E. DeVay. 1985. Soil solarization: effect on soil properties, crop fertilizers and plant growth. Soil Biol. and Biochem. 17:369-373.
54. Sundarum, T. K. 1986. Physiology and growth of thermophylic bacteria. p. 75. In: Thermophiles: General. Molecular, and Applied: Microbiology. T. D. Brock, ed. John Wiley and Sons, New York. 316 pp.
55. Suslow, T. V. and M. N. Schroth. 1982. Rhizobacteria of sugar beets: Effects of seed application and root colonization on yield. Phytopathol. 72:199-206.
56. Sztejnberg, A., S. Freeman, l. Chet, and J. Katan. 1987. Control of Rosellinia necatrix in soil and in apple orchard by solarization and Trichoderma harzianum. Plant Dis. 71:365-369.
57. Tjamos, E. C. 1984. Control of Pyrenochaeta Iycopersici by combined soil solarization and low dose of methyl bromide in Greece. Acta. Hort. 152:253-258.
58. Tjamos, E. C. and F. J. Paplomatas. 1988. Long-term effect of soil solarization in controlling verticillium wilt of globe artichokes in Greece. Plant Path. 37:507-515.
59. Usmani, S. M. H. and A. Ghaffar. 1982. Polyethylene mulching of soil to reduce viability off sclerotia of Sclerotium oryzae. Soil Biol. Biochem. 14:203-206.
60. White, G. J. and S. T. Buczacki. 1979. Observations on suppression on clubroot by artificial or natural heating of soil. Trans. Br. Mycol. Soc. 73:271-275.