7. Applications of soil solarization

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Solarization of agricultural materials for sanitation and control of plant pathogens
Achievements of soil solarization in Egypt
Control of soilborne pathogens with soil solarization in the southern region of Libyan Jamahiriya
Soil solarization in tropical agriculture for pre- and post-plant applications
Use of black plastic for soil solarization and post-plant mulching.
Post-plant application of soil solarization for tree crops
Use of solarization in marginally suitable climates
Soil solarization in a plastic house

Solarization of agricultural materials for sanitation and control of plant pathogens

Mohamed Besri
Professor, Institut Agronomique et Veterinaire, Hassan II, B.P. 6202 Rabat-lnstituts, Morocco

Introduction

About 8000 BC, man learned how to cultivate grain crops and also how to protect them. Through trials and errors of the centuries, many cultural and physical practices evolved for protecting crops from plant pests. Such measures as burning or ploughing under crop refuse, rotating crops, planting in the most favourable season, using healthy seeds, isolating crops, pruning and managing water and fertilizers, have been used for hundreds of years to improve the chances of making a good crop (11). The discovery in 1882 of the Bordeaux mixture encouraged many scientists to look for other chemicals that could kill pests (14). Other control methods such as biological control and solarization were later developed to protect various crops (7, 9).

The solarization technique which was developed in Israel (8) is used as a soil disinfestation method to control various soilborne fungi, nematodes and weeds (9). In Morocco, solar heating of the soil proved to be efficient in controlling some pathogens such as Fusarium oxysporum f. sp. lycopersici and Verticillium dahliae on tomato (4). Solarization was also successfully used to sterilize tomato supports for the control of Didymella Iycopersici (2, 3, 6).

Solarization of tomato supports for control of Didymella Iycopersici

Disease prevention and sanitation are important especially in intensive cultivation. In Morocco, tomato is one of the most economically important crops and ranks second in position of exported crops after citrus. This plant is grown all over the country, both in the open fields and in plastic houses. Tomato is attacked by many soil and airborne pathogens (1). Various methods are used to control these pathogens (i.e. plant resistance, cultural practices, and chemical control). Some tomato pathogens, such as Alternaria solani, Phytophthora infestans, Botrytis cinerea, are efficiently controlled by these control methods, but the control of other pathogens such as D. Iycopersici is very difficult to obtain by the same techniques.

Survival of Didymella Iycopersici - Didymella stem canker is one of the most destructive diseases of autumn-grown tomatoes in Morocco, particularly in the open fields. This disease is prevalent in all the tomato producing areas of the country, mainly during the wet and cold season, between October and January, which corresponds to the period of autumn tomato production.

Although farmers have been using various fungicides to control this pathogen, the incidence of the fungus remains very high.

For many years, the source of D. Iycopersici inoculum was unknown in Morocco. Various sources of inoculum such as crop residues (13), seeds and bamboo canes (10) were reported. In Morocco, crop residues are always removed at the end of the crop and the Geld is cleaned. The tomato seeds used are certified and are therefore pathogen-free. It has been shown that the pathogen survives mainly in the reed canes (Arundo donax) and in the Eucalyptus sp. stakes used to trellis the tomato plants. Besri (2, 3) reported that the incidence of the pathogen is higher in the plots where the plants are staked with supports regularly used in the tomato farms than in the plots where the tomato plants are supported with new stakes. With the stakes which have been frequently used, it was also observed that 90 percent of the Didymella stem cankers are located at the contact point between the tomato stem and the stakes and that the remaining cankers are located at soil level or at any other point of the stem. With the new tomato supports, more than 90 percent of the infected plants have cankers at levels where there is no contact between the support and the plant. It was also observed that in all the experimental plots, the percentage of the plants with cankers at soil level was very low. These results show that the soil plays a minor role in the fungus survival.

The pathogen was isolated from the stakes and its pathogenicity confirmed by tomato plant inoculation (2, 3). A good stake disinfection was obtained by different chemicals (unpublished dale). However, the chemical stake disinfested could not be applied at the farm level because of the huge quantity of stakes to be disinfested. Therefore, solarization was used for the disinfestation of stake (2, 3, 5, 6; Besri and Diop, 1985).

Solarization of the tomato supports - Infested tomato supports are displayed in June on wet soil and then covered with a white transparent polyethylene sheet (180 m ) which has been in use for three years as a cover to a plastic house. The maximum temperatures recorded under the polyethylene sheet were always higher than 50° 20°C, the maximum air temperature varying between 26°C and 34°C (5). The tomato stakes were solarized for three months June August), then used to support the tomato plants. IL was observed that solarization of the tomato stakes considerably decreases the incidence of D. Iycopersici and delays the disease occurrence (5). The high temperatures obtained under the polyethylene mulch killed the fungus and suppressed the primary inoculum.

However, at the farm level, the quantity of the tomato supports to be solarized is so high that the described solarization technique (5) could not be used and must therefore be adapted to the conditions for individual farms.

In Morocco, tomatoes for export are grown both in plastic houses (November - May) and in the open air (September - January). From June to October, the plastic houses are empty and the temperatures in these houses are higher than 50°C. Therefore, these houses could be used to solarize the stakes (from June to August) before their use as tomato supports. Besri (5) reported that the incidence of Didymella stem canker is considerably reduced when the tomato stakes are stored in the plastic houses instead of their storage in the open air. This new procedure of exposing the tomato stakes to high temperatures during summer months is simple and cheap. It presents excellent prospects for controlling D. Iycopersici and maybe other pathogens which survive in the stakes, in Morocco and in other countries with similar climates.

Conclusion

Sanitation includes all the practices that could be used to reduce the amount of plant pathogens in the field or in the greenhouse. D. Iycopersici survives mainly in the tomato stakes. The reduction of the available inoculum was obtained by solarization of sakes. Various other agricultural materials such as compost, manures, plastic foils used for mulching or covering crops, wires used for trellising tomatoes, have been found to carry pathogens (12). These agricultural materials could be disinfested by solarization. Therefore, collaborative research projects must be developed to make a complete inventory of the pathogens which are transmitted by these agricultural materials and find the best solarization procedures to be used for each kind of material.

References

1. Besri, M. 1975. Les principales maladies des solanacées observées au Maroc. Hommes, Terre et Eaux 16: 73-78.

2. Besri, M. 1982. Solar heating (solarization) of tomato supports for control of Didymella lycopersici stem canker. (Abstr.). Phytopathogy 72: 939.

3. Besri, M. 1982. Conservation et dissemination de Didymella lycopersici dans les cultures de tomate par les tuteurs. Phytopath. Z. 105: 1-10.

4. Besri, M. and A. Drame. 1982. Control of Fusarium oxysporum f.sp. lycopersici and Verticillium dahliae by soil solarization. Proceedings of the first meeting of the Arab Society for Plant Protection, Amman, 113.

5. Besri, M. 1983. Lutte contre le chancre Didymella Iycopersici de la tomate par chauffage solaire (solarisation) des tuteurs. Phytopath. Z. 108: 333340.

6. Besri, M. and Marguerite Diop. 1985. Lutte contre Didymella Iycopersici de la tom ate par stockage des tuteurs dans des tunnels plastiques : nouvelle application du chauffage solaire ou solarisation. Revue Horticole Suisse 58: 99-102.

7. Horsfall, J.G. and E.B. Cowling (eds.) 1977. Plant Diseases. An Advanced Treatise. Vol 1: How disease is managed. Academic Press, New York, 465 pp.

8. Katan, J., A. Greenberger, A. Alon and A. Grinstein. 1976. Solar heating by polyethylene mulching for the control of diseases caused by soil borne pathogens. Phytopathology 66: 683-688.

9. Katan, J. 1981. Solar heating (solarization) of soil for control of soilborne pests. Ann. Rev. Phytopathol. 19: 211-236.

10. Knight, D.E. and W.G. Keyworth. 1960. Didymella stem rot of outdoor tomatoes. Studies on sources of infection and their elimination. Ann. Appl Biol. 48:245-258.

11. Lucas, G.B., C.L. Campbell and L.T. Lucas. 1985. Introduction to Plant Diseases. Identification and Management. AVI Publishing Company, Inc., Wesport, Connecticut, 313 pp.

12. Palti, J. 1981. Cultural Practices and Infectious Crop Diseases. Springer. Berlin, Heidelberg, New York. 243 pp.

13. Phillips, D.H. 1956. Soil borne infection of tomatoes by Didymella Iycopersici. Trans. Brit. Mycol. Soc. 39: 330-340.

14. Torgeson, D.C. (ed.). Fungicides, An Advanced Treatise. Vol. 1(1967), Vol. 2 (1969). Academic Press, New York.

Achievements of soil solarization in Egypt

M.M. Satour, Ebtisam M. El-Sherif, L. El-Ghareeb, S.A. El-Hadad, and H.R. El-Wakil

Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt

Abstract

Results obtained so far indicate that soil solarization is very effective against several soilborne fungi, including the onion white rot fungus, Sclerotium Cepivorum, tomato crown rot fungi: Phytophthora parasitica, Pyrenochaeta lycopersecii, Pythium spp. and Rhizoctonia solani. Several nematodes were completely controlled as well as most of the common weed species, except Cyperus, and knot weed, which were partially controlled. Mulching soil, containing a high percentage of salt, resulted in reducing salinity by 30-50 percent due to the inability of water evaporation through the plastic sheets.

Solarization had a long-term effect (two or three seasons) for both disease control and increased crop yields.

Introduction

Soil solarization, the covering of moist soil with transparent polyethylene sheets during the hot months of June - August, is a relatively new method for controlling soilborne pathogens, fungi, nematodes, weeds and mites. This method was initially developed and improved in Israel (9, 21, 39). Currently, it is investigated in more than 25 countries including USA, Greece, Morocco, Iraq, Australia, Jordan and others (2, 22, 37). It was found to be effective against several fungal pathogens, nematodes, broom rape and a wide range of weeds (6, 7, 10, 11, 13, 14, 15, 17, 18, 23, 25, 32, 36, 40). Since most of these studies were carried out under sprinkler or drip irrigation, these do not insure similar success in furrow-irrigated soil, where pathogen spread is enhanced, leading to possible recontamination of disinfested soils. In Egypt, furrow-irrigation is very common, many soils have a long history of cropping, and the agricultural regimes for certain crops differ from those in countries where solarization was tested (27, 31, 34). This method has the advantage of being simple, relatively cheap, safe, and does not involve the use of toxic materials (3, 18, 19, 29). Results obtained by various workers from different countries have repeatedly shown that in many cases plant growth and yield were improved beyond disease control (IGR - phenomen) (7, 8, 12, 18, 21, 24, 29, 30, 33, 35, 38). Thus yield was increased even in soil without known pathogen(s).

This joint research programme has been carried out since 1984. The results are encouraging since soil solarization is effective under Egyptian conditions where furrow-irrigation is applied. A long-term effect was obtained and a better understanding of biological, chemical and physical changes occurring in the solarized soil was achieved (4, 5, 26). Some of the findings, e.g. effectiveness of solarization under furrow-irrigation and decreased soil salinity in solarized soils, are new to soil solarization and were first discovered in Egypt (1).

Various experiments carried out by the Egyptian team during the last five years, 1984-1989, were aimed to further study soil solarization, to improve its performance under local conditions, and to explore the potential positive and minimize its negative side-effects.

Materials and Methods

Field experiments were set up during 1984-1989, in various furrow-irrigated sites in Egypt, with a variety of crops: broad bean, onion, strawberry, tomato, corn, and Egyptian clover. The experiments were at Giza, Ismailia, Beni-Sweef, El-Fayoum and Qualyobia Governorates. The selected fields had a long history of cropping. Soil types were clay at Fayoum and Beni-Sweef, clay loam at Giza and Qualybia, and loamy sand and sand in Ismailia and some other field sites.

Experimental design - All experiments were carried out in four to five replicates, and were based on a basic unit (replicate) consisting of a bed 7 m wide and 14 to 54 m long, divided by eight irrigation furrows. Irrigation water was directed either separately to each plot or from solarized to non-solarized plots to reduce the chances of contamination, the supply canals were also solarized.

Soil solarization. - Solarized and non-solarized plots were pre-irrigated by flooding, irrigation furrows were opened manually one day later in the sandy soils and 4-8 days later in the other soils. Solarized plots were covered continuously using two transparent polyethylene sheets (7) (450 cm wide and 0.05 or 0.10 mm thick, Israeli and Egyptian products) containing ultra-violet absorbent (UVA). Solarization started usually in mid-July and lasted four to seven weeks. Soil temperatures were measured by a distance thermograph (Lambrecht, W. Germany). Typical maximal temperature in the open field of non-solarized soil, recorded at depth of 20 cm, was 35°C at Ismailia and Giza, while temperatures of the solarized soil were 8-15°C higher at Giza and Ismailia, respectively. Parameters used to evaluate the effectiveness of solarization included populations of soilborne pathogens and weed counts, disease rating, assessment of plant development at various stages and measurement of yield components. In one experiment, Rhizobium preparation was mixed with the seeds at a rate of 3 g per kg seeds. In the case of combining solarization with Ebtam, a herbide specially for Cyperus, 3 litres per fed were used; it was applied into the soil and mixed prior to mulching.

Salinity measurements - For loamy, sandy soil, a water-saturated paste was prepared and extracted and then electrical conductivity (EC) and concentrations of anions and cations were determined (17). Sulfate (S0₄2-) was calculated from the difference between the sums of concentrations of cations (Ca²⁺ Mg²⁺ + Na⁺ + K⁺) and that of the anions (HC0₃- + C1). For sandy soil, a 1:1 paste with water was prepared and EC was determined in the extract. Data were then corrected for saturation (26% ww) by multiplication. Soil was sampled according to the following procedure: the non-solarized and solarized plots were divided into three strips of 15 x 60 m each. Soil samples of about I kg were taken from 10 sites along the strip, then mixed into one composite sample, forming three composite replicates for each of the two treatments.

Soils of mulching plastic houses - Cucumber, pepper, and tomato, grown in plastic houses suffer from soilborne diseases. Currently, soil fumigation with methyl bromide and Dazomet are effective against most of the soilborne pathogens, Rhizoctonia solani, Fusarium spp., Phytophthora spp., and Pythium spp.

However, due to the increasing cost of both fumigants, as well as their impact on the environment, soil solarization is a possible replacement. Wet soil was treated with organic manure and mulched for six weeks and then prepared for transplanting of seedlings of the crop (28). Plastic houses were located at Ismailia and Giza Governorates. The temperature of the untreated soil reached 43°C at the depth of 20 cm, whereas in the solarized soil it reached 53°C.

Results

Data obtained so far indicate that soil solarization is an effective method for controlling various pests. Experimental results are summarized as follows:

A. Pathogenic fungi

1. White rot fungus: Sclerotium cepivorum

Various experiments carried out al Fayoum and Beni-Sweef indicated that solarization was effective against this pathogen. In Beni-Sweef, particularly, in the first year after solarization, growth of onions in the solarized plots was significantly improved and the white rot disease was completely controlled (Table 1). Disease progressed further in the non-solarized plots reaching 50 percent by the end of the season, as compared to zero in the solarized plots. A long-term effect of solarization in the second and third year was evident. The build-up of the disease in the non-treated plots was rapid, leading to a complete destruction of the plants.

2. Fusarium basal rot:

Solarization treatments at Fayoum, improved growth of onions and reduced basal rot incidence by 84-96 percent and increased the yield by 151-207 percent.

3. Seedborne pathogens:

Solarization increased onion seed yield by 218 percent (Table 2), when bulbs, previously grown in a solarized soil at Fayoum, were planted again in the second year for seed production. In addition, seeds harvested from solarized plots were less contaminated with Fusarium.

4. Broad bean root rot

This crop is a very important winter crop in Egypt. It is suffering mostly from broomrape, root rot and leaf spot fungi, especially in the wet winters. Experimentation with this crop indicated that root rot pathogens, especially Rhizoctonia solani, could be controlled to at least 86 percent by solarization compared with non-solarized plots.

5. Tomato root and crown rot:

Tomato plants are infected by one or more of various soilborne fungi in Egypt including R. solani, Phytophthora parasitica, Pythium spp., and Pyrenochaeta lycopersici.

B. Weed control

Weed contamination of various agricultural lands in Egypt is mainly due to the furrow system of irrigation adapted in the old land, and in the adjacent new land. Weed seeds and plant parts may move from one site to another through the irrigated canals.

Soil solarization has proved to be very effective in controlling several genera of weeds, except Cyperus (50-93 percent). However, the level of killing of this weed depends on soil moisture: the higher the moisture content prior to mulching, the higher the level of killing.

Broomrape was controlled by solarization. It could be controlled for two successive years, in broad bean or in tomato fields, by one treatment.

In general, various weeds were also controlled, completely or partially (75-100 percent), by soil solarization, these included Amaranthus sp., Portulaca spp., Plantago spp., Chenopodium murale, Vicia sp., Lactuca scariola, Beta vulgaris, Rumex dentatus, Cynodon dactylon, Coronopus squamatus, and Sisymbrium irio.

In contrast, Malva spp., Melilotus indica and Convolvulus arvensis were less affected by solarization with less than 75 percent killing.

C. Salinity

During an early experiment at Fayed, Ismailia in 1981, where the soil is saline, mulching improved the growth and stand of bean plants. The surface of the soil of the treated plots did not show any accumulation of the salt when compared with non-solarized plots. The electrical conductivity of the upper layer, 0-10 cm, of both treatments was determined; it was 11 000 and 19 000 ppm for solarized and non-solarized soils, respectively.

Experiments carried out at Sinai, Ismailia and Fayoum were checked by local scientists and Dr Y. Chen from Israel to ensure this finding.

The results of these tests showed a strong reduction in the concentration of Na⁺, Cl^- and an increase in NO₃^- concentration.

It is assumed that the higher salinity of the untreated soil results from the upward movement of salt from a source in a deeper soil layer, probably a ground water table close to the surface. In the solarized soil, evaporation is almost completely eliminated, thus the transport of solution, and the consequent salt accumulation, is reduced.

Discussion and Conclusion

Soil solarization is effective in controlling soilborne pests and improving plant growth and yield in a variety of Egyptian soil sand crops under furrow-irrigation in fields with a long history of cropping. In addition, a long-term effect was found in this study despite the fact that, because of furrow-irrigation and the continuous cultivation of successive crops, certain levels of recontamination could be avoided. The two pre-requisites for a long-term effect by solarization are a drastic reduction of pathogen inocula and the induction of soil suppressiveness to retard reinfestation from various sources.

Soil solarization is not effective in all cases. Thus, in this study, Cyperus was not satisfactorily controlled. Combining solarization with other methods, chemical or biological means of control, could improve the results. For that reason, solarization was combined with Ebtam, a selective weed killer for Cyperus, at a half dose 3 1/acre, prior to mulching; the combination completely (100 percent) controlled this weed (Sarabyoum - Ismailia, 1988/89).

Plant growth and yield improvement, in the absence of known pests, could be attributed to a variety of chemical, physical, and biological factors. In this study, salt concentration reduction by mulching is reported. The latest report (41), indicated that solarization controlled potassium potassium syndrome in cotton in California, through the control of unknown pathogen(s) which interfere with translocation of this element into the upper parts of the plants.

Soil solarization in plastic houses was satisfactory when compared with other methods of soil sterilization, methyl bromide and Basamid. Several hundred plastic houses, 500 m2 each, were solarized during the last three years in Egypt, and the results were similar to other treatments in controlling various soilborne pathogens and weeds; in addition no pesticide residues were present.

Literature Cited

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, Egyptian soils. Pl. Dis. 72: 143-146.

2. Avidov, E., N. Aharonson, J. Katan, B. Rubin, and O. Yarden. 1985. Persistence of terlutryn and atrazine in soil as affected by soil disinfestation and fungicides. Weed Science 33:457-461.

3. Avissar, R., Y. Mahrer, L. Margulies, and J. Katan. 1986. Field ageing of transparent polyethylene mulches: I - Photo-metric properties. Soil Sci. 50: 202-205.

4. Blaker, N.S. and J.D. MacDonald. 1985. Effect of soil salinity on the formation of sporangia and zoospores by three isolates of Phytophthora Phytopathology 75: 270-274.

5. Chen, Y. and J. Katan. 1980. Effect of solar heating on soils by transparent polyethylene mulching on their chemical properties. Soil Sci. 130:271 277.

6. Davis, J.R. and L.H. Sorensen. 1986. Influence of soil solarization at moderate temperatures on potato genotypes with differing resistance to Verticillium dahlias. Phytopathology 76: 1021-1026.

7. Elad, Y., J. Katan, and I. Chet. 1980. Physical, biological and chemical control integrated for soil-borne diseases in potatoes. Phytopathology 70: 418422.

8. Frank, Z.R., Y. Ben-Yephet, and J. Katan. 1986. Synergistic effect of metham and soil solarization in controlling delimited shell spots of peanut pods. Crop Prot. 5: 199-202.

9. Genis, J.L. 1989. Temperature evaluation in solarized soils by fourier analysis. Phytopathology 79: 506-510.

10. Gerson, U., S. Yathom, and J. Katan. 1981. A demonstration of bulb mite control by solar heating of the soil. Phytoparasitica 9: 153-155.

11. Giblin-Davis, R.M., and V.D. Stephen. 1988. Solarization for nematode disinfestation of small volumes of soil. Annals of Applied Nematology 2:4145.

12. Greenberger, A., Anat Yogev, and 1. Katan. 1987. Induced suppressiveness in solarized soils. Phytopathology 77: 1663-1667.

13. Grinstein, A., D. Orion, A. Greenberger and J. Katan. 1979. Solar heating of the soil for the control of Verticillium dahlias and Pratylenchus thornei in potatoes. pp. 431-438. In: Soil-borne plant pathogens. B. Schippers, and W. Gams, (Eds.) Academic Press, London.

14. Grinstein, A., 1. Katan, A. Abdul-Razik, O. Zeidan and Y. Elad. 1979. Control of Sclerotium rolfsii and weeds in peanuts by solarheating of soil. Pl. Dis. Reptr. 63: 1056-1059.

15. Hough, A., N.J. Mulder, and J.M. La Grange. 1979. Heat treatment for the control of Phytophthora gummosis incitrus. Pl. Dis. Reptr. 63: 40-43.

16. Hussein, A.M., N.F. Somer, and R.J. Fortlage. 1986. Suppression of Aspergillus flavus in raisins by solar heating during sun drying. Phytopathology 76: 335-338.

17. Jacobsohn, R., A. Greenberger, J. Katan, M. Levi, and H. Alon. 1980. Control of Egyptian broomrape (Orobanche aegyptica) and other weeds by means of solar heating of the soil by polyethylene mulching. Weed Science 28: 312-316.

18. Katan, J. 1979. Solar heating of soil and other economically safe methods of controlling soil-borne pests for increasing food production. In: Proceedings of Symposia IX International Congress of Plant Protection 1: 26-30.

19. Katan, J. 1980. Solar pasteurization of soils for disease and control: Status and prospects. Pl. Dis. 64: 450-454.

20. Katan, J. 1981. Solar heating solarization of soil for control of soilborne pests. Ann. Rev. Phytopath. 19: 211-236.

21. Katan, J., A. Greenberger, H. Alon, and A. Grinstein. 1976. Solar heating by polyethylene mulching for the control of diseases caused by soilborne pathogens. Phytopathology 76:683-688.

22. 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(3): 229-255.

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24. Kalan, J., G. Fishler, and A. Grinstein. 1983. Short and long term effects of soil solarization and crop sequence on Fusarium will and yield of cotton in Israel. Phytopathology 73: 1215-1219.

25. Katan, J., I. Rotem, Y. Finkel and J. Daniel. 1980. Solar heating of the soil for the control of pink root and other soil-borne diseases in onions. Phytoparasitica 8: 39-50.

26. Mahrer, Y. and J. Katan. 1981. Spatial soil temperatures regime under transparent polyethylene mulch, numerical and experimental studies. Soil Sci. 131: 82-87.

27. Mahrer, Y., O. Naot, E. Rawitz, and J. Katan. 1984. Temperature and moisture regimes in soils mulched with transparent polyethylene. Soil Sci. 48: 362-367.

28. Mahrer, Y., R. Avissor, O. Naot, and J. Katan. 1987. Intensified soil solarization with closed greenhouses: numerical and experimental studies. Agricultural and Forest Meteorology 41: 325-334.

29. Martyn, R.D. and T.K. Hartz. 1986. Use of soil solarization to control Fusarium wilt of watermelon. Pl. Dis. 70: 762-766.

30. Materazzi, A., E. Triolo, G. Vannacci, and G. Scaramuzzi. 1987. Soil solarization of Sclerotinia minor infected soil in a greenhouse. Colture Protette 10: 51-54.

31. Naot, O., Y. Mahrer, E. Ravitz, R. Avissor, and J. Katan. 1987. The effect of reirrigation on the thermal regime of polyethylene-mulched soils: experimental and numerical. Soil Science 144: 101-106.

32. Pullman, G.S. J.E. DeVay, R.H. Garber, and A.R. Weinhold. 1981. Soil solarization effects on Verticillium wilt of cotton and soil-borne populations of Verticillium dahliae, Pythium spp., Rhizoctonia solani and Thielaviopsis basicola. Phytopathology 71: 954-959.

33. Pullman, G.S., J.E. DeVay, and R.H. Garber. 1981. Soil solarization and thermal death logarithmic relationship between time and temperature for four soilborne plant pathogens. Phytopathology 71: 959-964.

34. Ramirez-Villapudua, J. and D.E. Munnecke. 1988. Effect of solar heating and soil amendments of cruciferous residues on Fusarium oxysporum, f. sp. conglutinans and other organisms. Phytopathology 78: 289-295.

35. Stapleton, J.J., B. Lear, and J.E. DeVay. 1987. Effect of combining soil solarization with certain nematicides on target and nontarget organisms and plant growth. Annals of Applied Nematology 1: 107-112.

36. Stapleton, JJ. and J.E. DeVay. 1986. Soil solarization: a nonchemical approach for management of plant pathogens and pests. Crop. Prot. 5: 190-198.

37. Stapleton, J.J. and J.G. Garza-Lopez. 1988. Mulching of soils with transparent (solarization) and black polyethylene films IO increase growth of annual and perennial crops in south western Mexico. Trop. Agric. (Trinidad) 65: 29-33.

38. Sztejnberg, A., S. Freeman, I. Chet, and J. Katan. 1987. Control of Rosellinia necatrix in soil and in apple orchards by solarization and Trichoderma harzianum. Pl. Dis. 71:365-369.

39. Michailides, T. J. and J. M. Ogawa. 1989. Effect of high temperatures on the survival and pathogenicity of propagules of Mucor piriformis. Phytopathology 79:547-554.

40. Vannacci, G. E. Triolo and A. Materazzi. 1988. Survival of Sclerotinia minor Jagger sclerotia in solarized soil. Plant and Soil 109: 49-55.

41. Weir, W.L., R.H. Garber, J.J. Stapleton, R. Felix-Gastelum, RJ. Wakeman, and J.E. DeVay. 1989. Control of potassium deficiency syndrome in cotton by soil solarization California Agriculture 43(3): 26-28.

Table 1. Effect of soil solarization on Sclerotium cepivorum, the causal organism of white rot disease of onion. Kafr-Naser Beni-Sweef. 1986/1987- 198811989

Table 2. Onion seed production when soils were solarized by sun heating through polyethylene sheets. Fayoum - 1985/1986

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