Soil solarization as a substitute for methyl bromide fumigation in greenhouse tomato production in Cyprus

Preplant soil fumigation with methyl bromide (MB) is presently standard practice in greenhouse tomato production. Since this compound is scheduled to be phased out by 2005, the possibility of using solarization as an alternative soil disinfestation method was examined in four greenhouse tomato trials. Solarization was applied for 8 weeks in July-August, using transparent polyethylene sheets for soil mulching, and compared with MB fumigation applied in September, before planting, at 80 g/m². Solarization raised the maximum soil temperature by 9°C and reduced the population density ofFusarium spp. in soil by 91–98%. Similar reductions of soil inoculum (95–99%) were obtained with MB fumigation. Both methods provided effective control of Fusarium wilt, Verticillium wilt and corky root rot on tomato plants. MB fumigation was in addition highly effective against root-knot nematodes, whereas nematode control with solarization did not exceed 50%. Both treatments resulted in similar fruit yield increases, ranging within 90–140% compared with plants grown in untreated soil. During the second cropping season following soil treatment, solarization exhibited two times higher residual effectiveness against vascular wilt diseases compared with MB fumigation. The latter treatment, however, was superior to solarization in its residual effectiveness against root-knot nematodes and to a lesser extent against corky root rot. Fruit yields from solarized and MB-fumigated soil during the second cropping season were higher than those obtained from untreated soil by approximately 35% and 60%, respectively. In Cyprus, solarization appears to be an effective alternative to MB fumigation in greenhouse tomato production, especially if integrated with other approaches enabling more effective nematode control.     

Solarization of soil in piles for the control of Meloidogyne incognita in olive nurseries in southern Spain

The potential of solarization to control Meloidogyne incognita in piles of soil used at olive nurseries in southern Spain was studied in 1999 and 2000. Kaolin and soil infested with free eggs and egg masses of the nematode in nylon bags were buried 20 and 40 cm deep inside conical piles of soil 80 cm high and with a base diameter of 1 m. Soil piles were solarized for 3 weeks in July and August. The effect of various periods of solarization was assessed by egg hatch bioassays in sterile water, and by infectivity to tomato plants. Maximum soil temperature at 20 cm depth in solarized piles was 47·4°C in 1999 and 48·2°C in 2000, compared with 32·9°C and 31·7°C in nonsolarized piles. Solarization reduced egg hatch by > 95% compared with nonsolarized samples, irrespective of type, burial depth and location of inocula in a soil pile. Egg hatch of egg mass-infested samples buried at 20 cm depth was higher than that of free eggs buried at the same depth. The differential effect associated with burial depth and type of inoculum was not found in solarized piles. In nonsolarized piles, hatch of free eggs from samples buried at 40 cm depth was higher than that from samples buried at 20 cm depth. Egg hatch in samples from solarized piles was lower than that from nonsolarized piles. A bioassay of tomato plants in 2000 confirmed the reduction in infectivity of free eggs buried in solarized soil piles. Under the conditions in southern Spain, solarization of 40 cm-high piles of soil for 3 weeks can therefore be used for the control of root-knot nematodes in potting soil for olive nursery production.     

The effect of solar heating of soil on natural and inoculated agrobacteria

Solarization trials were carried out over 3 years and in two countries to control crown gall disease on fruit trees and eliminate Agrobacterium . In 1992, agrobacteria in naturally infested soils of two Italian nurseries were monitored before and after solarization. Agrobacteria populations decreased by 99% and 92% after the treatment; however, crown gall incidence did not decrease. In 1993 and 1994 solarization was tested in Oregon in fields artificially infested with two marked strains of A. tumefaciens . In sandy loam soil, the target bacteria were eliminated in 4 weeks, while in silty clay soil the populations were markedly reduced after 2 months of treatment. Crown gall incidence on cherry rootstocks transplanted to the field at the end of 1993 was 3.7% in the sandy loam soil control plots, while no tumours were observed on plants from solarized plots. The use of solarization in combination with reduced doses of metham-sodium was also evaluated.     

Fusarium wilt of watermelon in Cyprus and its management with soil solarization combined with fumigation or ammonium fertilizers

Fusarium wilt is a limiting factor to watermelon production in Cyprus. In previous studies, soil solarization applied in 1-m-wide strips provided only partial disease control. In order to improve the effectiveness of solarization, three field experiments were carried out in heavily infested soils, using various solarization techniques, alone or in combination with methyl bromide fumigation or soil amendments with ammonium-based fertilizers. Increasing the width of the solarization strip from 1 to 2 m had no significant influence on its effectiveness. Solarization with a double rather than single polyethylene sheet, in either 1- or 2-m-wide strips, improved slightly the level of wilt control but had no significant effect on yield. Combined solarization–methyl bromide treatments, however, improved significantly the level of wilt control and increased marketable yield by up to 100% over that obtained with either method alone. The low rate of methyl bromide (50gm⁻²) was as effective as the normal rate used by growers (100 g m⁻). Soil amendment with ammonium-based fertilizers improved even more the effectiveness of solarization and increased yield by up to 200% over that obtained with solarization alone. Best results were obtained with ammonium sulphate or monoammonium phosphate at a rate equivalent to 180 kg N ha⁻¹.     

Adaptation of soil solarization to the integrated management of soilborne pests of tomato under humid conditions

ABSTRACT Soil solarization was shown to be cost effective, compatible with other pest management tactics, readily integrated into standard production systems, and a valid alternative to preplant fumigation with methyl bromide under the tested conditions. Solarization using clear, photoselective, or gas-impermeable plastic was evaluated in combination with metham sodium, 1,3-dichloropropene + chloropicrin, methyl bromide + chloropicrin, pebulate, or cabbage residue. Strip solarization, applied to 20-cm-high, 0.9-m-wide beds, was conducted to achieve compatibility with standard production practices and resulted in soil temperatures 2 to 4 degrees C above those temperatures resulting when using conventional flatbed solarization. Soil temperatures were 1 to 2 degrees C higher at the edges of the raised beds, eliminating any border effects associated with solarization. Following a 40- to 55-day solarization period, the plastic was painted white and used as a production mulch for a subsequent tomato crop. The incidence of Southern blight and the density of Paratrichodorus minor and Criconemella spp. were lower (P < 0.05) in solarized plots. No differences (P < 0.05) in the incidence of Fusarium wilt and the density of nutsedge and Helicotylenchus spp. were observed between plots receiving solarization and plots fumigated with a mixture of methyl bromide + chloropicrin. The severity of root galling was lower (P < 0.05) when soil solarization was combined with 1,3-dichloropropene + chloropicrin (16.2 + 3.4 g/m(2)) and a gas-impermeable film. The incidence of bacterial wilt was not affected by soil treatments. Marketable yields in plots using various combinations of soil solarization and other tactics were similar (P < 0.05) to yields obtained in plots fumigated with methyl bromide + chloropicrin. The results were validated in several large scale field experiments conducted by commercial growers.     

Long-term effect of soil solarization in controlling verticillium wilt of globe artichokes in Greece

Soil solarization, either singly or in combination with a reduced dosage (34 g/m²) of methyl bromide, was effective in controlling verticillium wilt of globe artichokes for three successive cropping seasons. Both treatments resulted in greatly reduced natural populations of Verticillium dahliae microsclerotia, which were positively correlated with significant reductions in diseased plants as well as with the early formation of primary artichoke heads and increased yield. Propagules of Talaromyces flavus increased and survived better in solarized than in solarized and fumigated soils and could be partially involved in the effectiveness of solarization. Propagules of Aspergillus terreus invariably increased in treated plots but their involvement in the longevity of the treatment is questionable.     

Long term effect of soil solarization on soil properties and cauliflower vigor

The effect of soil solarization on physical, chemical and biological properties of soil was studied, along with the response of cauliflower seedlings following solarization. Nursery beds were covered with transparent polyethylene sheet and soil temperature and moisture were recorded. Soil samples were collected five times for analysis. Three cauliflower nurseries were raised at 30-day intervals; germination was recorded 10 days after sowing and seedling length 30 days after sowing. The maximum temperature in solarized soil ranged from 40.2–47.2°C, with an increase of 5.2° to 9.9°C over non-solarized soil. There was a conservation of 5.48% moisture in solarized soil as compared with non-solarized. Solarization significantly increased electrical conductivity, organic carbon, nitrogen and potassium over pre-solarized soil. The mean pH, EC, Ca, Mg, N, P, K and C recorded in solarized soil was higher than in non-solarized. Soil solarization reduced the population of fungi from 25.68 x 10⁴ to 4.8 x 10⁴, bacteria from 20.28 x 10⁶ to 5.66 x 10⁶, actinomycetes from 31.60 x 10⁵ to 4.40 x 10⁵, and reduction in population was recorded even after 90 days, when compared with non-solarized soil. Solarization effectively reduced (>97%) population of plant parasitic and free living nematodes. Cauliflower seedlings in solarized soil had a better vigor index than non-solarized soil. Present findings reveal that soil solarization could be exploited for nutrient management and soilborne pests control, with a better vigor index of vegetable nursery.     

The effects of soil solarization on sclerotial populations of Sclerotinia sclerotiorum

Solarization reduced the populations of sclerotia of Sclerotinia sclerotiorum in soil and reduced the ability of the surviving sclerotia to form apothecia. The greatest reductions occurred in the top 5 cm layer of soil but significant effects were seen at 10 and 15 cm depths. These reductions were due mainly to microbial colonization and degradation of sclerotia weakened by the sublethal temperatures produced by solarization. A beneficial side-effect was a significant reduction in the population of weeds in solarized plots.     

Assessment of the differential response of weeds to soil solarization by two methods

The efficacy of solarization in weed control under field conditions of the United Arab Emirates was evaluated by two methods: on-farm weed assessment and a seed germination test. In the on-farm weed assessment method, the weed frequency, density, and dry weight were compared in the solarized and non-solarized plots that were cultivated with cabbage. Prior to solarization, the soil was artificially infested with the seeds of 10 weeds. Generally, the densities of seven species and dry weights of five species were significantly lower in the solarized plots as compared to the control. Launea mucronata , Capsella bursa-pastoris , and Echinochloa colona were very sensitive to solarization, as they did not appear in the solarized plots. However, Portulaca oleracea and Melilotus indica were not significantly affected by soil solarization. In the second method, the germination was assessed for the seeds of four weedy species buried at three depths for different durations of solarization. The results confirmed the great sensitivity of L. mucronata and C. bursa-pastoris seeds to solarization, as all had not germinated after 15 days of solarization, even at the 15 cm depth. The seeds of E. colona , however, were less sensitive after 15 days of solarization, especially at 7.5 cm and 15 cm, respectively. The seed germination method confirmed the resistance of the P. oleracea seeds to solarization. The results emphasized the importance of the germination test to provide accurate predictions about the spatial and temporal changes of the soil seed bank in solarized farms. This would help to determine the optimal duration of solarization in each farm, depending on the kind of weeds infesting the farm.     

Soil solarization for the control of verticillium wilt of greenhouse tomato

Verticillium dahliae, the causal agent of Verticillium wilt of tomato, causes serious damage to crops grown in unheated greenhouses. To control this disease, growers are obliged to employ strong soil disinfestants. The possibility of controllingV. dahliae by using soil solarization during the months of June — August was examined. The soil was covered with transparent polyethylene sheets for 10 weeks. The pathogen could not be isolated from the solarized soil, whereas the inoculum level in the nonsolarized soil remained high (1379–1806 propagules/g soil). The yield from the solarized soil was increased by 112.4% in comparison with the control, and no infected plants were observed. The percentage of infected roots was very low (0.3–0.4%) in relation to the nonsolarized soil (66.7–67.1%). From these results it was concluded that solarization can effectively control Verticillium wilt of greenhouse-grown tomato under the summer conditions in Crete.     

Effect of soil solarization on the control of Phytophthora root rot in avocado

Phytophthora root rot is of paramount importance in avocado orchards of southern Spain. Soil solarization has been demonstrated to control the pathogen in infested areas from which infected trees had been removed. We aimed to determine whether soil solarization in established avocado orchards controls the disease. Soil solarization increased average maximum hourly soil temperatures by 6.5–6.9°C in unshaded areas of avocado orchards in coastal areas of southern Spain, depending on depth and year. The corresponding temperatures in shaded areas were c. 2–3°C lower. P. cinnamomi in soil, on infected avocado rootlets, and in a nutrient substrate buried at 30–60 cm depth was reduced to negligible amounts after 6–8 weeks of solarization in both unshaded and shaded locations of avocado orchards. P. cinnamomi could not be detected in avocado rootlets up to 14 months later, suggesting a long-term effect. Soil solarization did not affect growth of the trees, and fruit yields were increased as compared with control plots. Following soil solarization for 3 weeks from mid-July 1994, when maximum hourly temperatures reached 33–36°C, P. cinnamomi could not be recovered from a depth of up to 45 cm in unshaded areas or from a depth of up to 30 cm in shaded areas after the initial 10-day period. The viability of inoculum of the pathogen buried at depths between 15 and 60 cm in bare soil was determined by sequential sampling in two solarization experiments starting 12 June and 4 July 1995, respectively. In the first experiment, P. cinnamomi could not be detected at any depth after 4–8 weeks of solarization in unshaded areas but could be recovered at all depths except 15 cm in shaded areas. In the second experiment, where temperatures were higher and the soil surface not shaded, P. cinnamomi could not be recovered after 2 weeks at 15 and 30 cm.     

Establishment of apricot and almond trees using soil mulching with transparent (solarization) and black polyethylene film: effects on Verticillium wilt and tree health

Apricot ( Prunus armeniaca ) and almond ( P. dulcis ) trees at the first leaf stage were planted in soil infested with Verticillium dahliae and mulched with transparent or black polyethylene film, or not mulched, in the San Joaquin Valley of California, March-August 1990. During the 19-week mulching treatment, summer soil temperatures reached as high as 46, 41, and 33°C at 18 cm depth; and 41, 37, and 32°C at 30 cm depth under clear film, black film, and no film, respectively. Trees mulched from the time of planting with transparent polyethylene (solarization) did not survive or grow as well as those mulched with black film or not mulched. Incidence of foliar symptoms due to Verticillium wilt was reduced by 86–100% in both apricot and almond trees by black, as well as transparent film mulch the following season. Incidence of vascular discoloration symptoms of trunks and primary scaffolds due to Verticillium wilt was similarly reduced by both mulches. Mulching with black polyethylene film gave better overall results than solarization with transparent film. The intermediate soil temperatures produced did not chronically harm trees, as judged by tree survival and annual growth of trunk diameter, yet the prolonged period of soil heating provided control of Verticillium wilt equivalent to that of solarization with transparent polyethylene. These studies provided further evidence that in-season mulching can be used to conserve water during establishment of new orchards or replant trees in warm, arid climates.     

Use of soil solarization for controlling bacterial canker of tomato in plastic houses in Greece

Soil solarization provided effective control of bacterial canker of tomato in plastic houses. Trials in plastic houses in Preveza County, Greece, during the period 1990–1992 showed that soil solarization (approximately 6 weeks of soil mulching with transparent polyethylene sheets) drastically reduced disease incidence throughout the cropping season. In contrast, soil fumigation with a recommended rate of methyl bromide (70 g/m²) was ineffective. Both wild-type and antibiotic-resistant strains of Clavibacter michiganensis subsp. michiganensis , growing on Nutrient Agar Glycerol (NAG) medium within covered and screwed vials and embedded at various soil depths (5, 15 or 25 cm) before soil solarization, were studied. Weekly sampling of bacteria during treatment showed a sharp decline of populations in the solarized soil compared to the non-treated control plots 4–6 weeks after soil tarping. Populations of marked strains infiltrated into tomato stem segments and buried in the soil decreased significantly after 5–6 weeks of solarization compared to non-treated control plots. The data presented here suggest that soil solarization is useful for the control of bacterial canker of tomato in plastic houses in Greece.     

Physiological races and soil population level of fusarium wilt of watermelon

Results of a comparative test oflocal isolates ofFusarium oxysporum f. sp.niveum with isolates from abroad indicate the existence of a highly virulent race of this fungus in Israel. All these isolates were found also pathogenic to resistant cultivars from the U.S.A. When inoculum density was tested, a one-hundredfold higher fungus population was required for extensive wilt of watermelon seedlings in freshly infested sterilized soil compared with the same soil kept dry for three months. In naturally infested soil, where almost 100% of the plants were infected toward the end of the season, the lowest count of the fungus population (400 propagules/g soil) was comparable to the inoculum density required for total wilt of watermelon seedlings in infested sterilized soil.     

Combined soil treatments and sequence of application in improving the control of soilborne pathogens

ABSTRACT The effects of reduced doses of methyl bromide (MB) or metham sodium, heating, short solarization, and soil microbial activity, alone or in combination, on survival of soilborne fungal pathogens were tested in a controlled-environment system and field plots. Sublethal doses of heating or MB delayed germination of Sclerotium rolfsii sclerotia. Combining MB and heating treatments was more effective than either treatment alone in controlling S. rolfsii and Fusarium oxysporum f. sp. basilici. The application heating followed by fumigation with MB, was significantly more effective in delaying and reducing germination of S. rolfsii sclerotia and in controlling F. oxysporum f. sp. basilici than the opposite sequence. Further, incubation in soil and exposure to microbial activity of previously heated or MB-treated sclerotia increased the mortality rate, indicating a weakening effect. Similarly, incubation of chlamydospores of F. oxysporum f. sp. melonis and F. oxysporum f. sp. radicis-lycopersici in soil in the field after fumigation further reduced their survival, confirming the laboratory results. In field tests, combining MB or metham sodium at reduced doses with short solarization was more effective in controlling fungal pathogens than either treatment alone. Treatment sequence significantly affected pathogen control in the field, similar to its effect under controlled conditions. This study demonstrates a frequent synergistic effect of combining soil treatments and its potential for improving pathogen control and reducing pesticide dose, especially when an appropriate sequence was followed.     

Weed control in squash and tomato fields by soil solarization in the Jordan Valley

Black (BPE) and clear polyethylene mulches (CPE), 0.08 and 0.06 mm thick, respectively, were compared for their effectiveness for soil solarization over three seasons during 1986–1989 in weedy fields. Solarization for 6 weeks reduced weed growth and enhanced crop yields. However, further mulching with BPE after solarization with either BPE or CPE gave the best results. Not all weeds were sensitive to solarization. Some weed species were completely controlled; others were reduced to varying degrees; yet other weed species seemed to be enhanced by solarization. Solarization without further mulching was no better than farmer-practice in reducing weed growth or in increasing crop yield. Weeds required further removal after the middle of the growing season. Any soil disturbance after solarization reduced the weed control effect of solarization. Crops grew best in plots after solarization with BPE if they were planted in the same mulch after it was perforated.     

Solarization; a physical control method for weeds and parasitic plants (Orobanche spp.) in Mediterranean agriculture

Summary. Experiments were conducted between 1985 and 1988 to evaluate the effect of duration and time of solarization on the control of two broom rapes ( Orobanche aegyptiaca Pers., O. crenata Forsk.) and other weeds common in the fields of faba bean ( Vicia faba L.) and lentil ( Lens culinaris Medik.) in West Asia. Solarization was performed by applying clear polyethylene sheet to the soil for 0, 10, 20, or 40 days in 1985/86, 0, 30, or 40 days in 1986/87 and 0, 20, 30, 40 or 50 days in 1987/88 during the hot season (July and August) and for 50 days immediately before sowing during milder weather (September and October) in 1986/87. Best control was obtained with solarization for 30–50 days in the hot season. Maximum soil temperature under polyethylene at 5 cm was 55°C in 1985, 48°C in 1986 and 57°C in 1987. Broomrape dry weight decreased in the first experiment by more than 90% in both faba bean and lentil fields. Solarization controlled broom-rape and other weeds in the following two seasons when the soil was left undisturbed during the season of the treatment.     

Evaluation of soil solarization for control of root diseases of row crops in Victoria

The effect of soil solarization on the viability of plant pathogens and disease was evaluated in Victoria. The treatment was tested in NW and S Victoria with natural soil inoculated with high inoculum levels of Eusarium oxysporum, Plasmodiophora brassicae, Sclerotium cepivorum, Sclerotinia minor, Sclerotinia sclerotiorum, Verticillium dahliae and the nematodes Meloidogyne javanica and Pratylenchus penetrans. Other experiments were established at sites with a previous history of disease.
Solarization of artificially inoculated soils reduced inoculum levels to at least a depth of 10 cm and effectively controlled diseases caused by P. brassicae on broccoli, and S. minor and S. sclerotiorum on lettuce. The treatment reduced inoculum levels but not disease of carnations and watermelons affected by E. oxysporum , tomatoes affected by M. javanica , celery affected by P. penetrans , and onions affected by S. cepivorum. Results were inconclusive for tomatoes affected by V. dahliae.
Experiments in naturally infested soils established that solarization reduced disease and increased yields of Chinese cabbage affected by P. brassicae , celery affected by P. penetrans , lettuce affected by S. minor and watermelon affected by root rot.
Solarization reduced disease of onions affected by S. cepivorum but did not significantly increase yield. At all sites the treatment reduced the number of viable propagules of the pathogens to at least a depth of 10 cm.     

Comparative effects of soil solarization with single and double layers of polyethylene film on survival ofFusarium oxysporum F. SP.Vasinfectum

Soil solarization (SoSol) with a single layer of transparent polyethylene (PE) film, traps considerable heat and moisture in soil. Solarization of field soil with two layers of 1 mil (25 μm thick) PE film, separated by a 6-cm air layer, caused soil temperatures at 15 cm depth to rise by 12.7°C and 3.6°C over those in noncovered soil or soil covered by one layer of film, respectively; at 30 cm depth the respective differences in temperature were 11.2°C and 2.7°C. Viability of propagules (mainly chlamydospores) ofFusarium oxysporum f. sp.vasinfectum that had been buried at 30 cm depth, was reduced after 31 days of solarization by 97.5%, 58%, and 0% under a double film layer, a single layer, and in non-covered soil, respectively. The insulating effect of a double layer of PE film improved heat retention in soil and the solarization effect.     

In planta and soil quantification of Fusarium oxysporum f. sp. ciceris and evaluation of Fusarium wilt resistance in chickpea with a newly developed quantitative polymerase chain reaction assay

Fusarium wilt of chickpea caused by Fusarium oxysporum f. sp. ciceris can be managed by risk assessment and use of resistant cultivars. A reliable method for the detection and quantification of F. oxysporum f. sp. ciceris in soil and chickpea tissues would contribute much to implementation of those disease management strategies. In this study, we developed a real-time quantitative polymerase chain reaction (q-PCR) protocol that allows quantifying F. oxysporum f. sp. ciceris DNA down to 1 pg in soil, as well as in the plant root and stem. Use of the q-PCR protocol allowed quantifying as low as 45 colony forming units of F. oxysporum f. sp. ciceris per gram of dry soil from a field plot infested with several races of the pathogen. Moreover, the q-PCR protocol clearly differentiated susceptible from resistant chickpea reactions to the pathogen at 15 days after sowing in artificially infested soil, as well as the degree of virulence between two F. oxysporum f. sp. ciceris races. Also, the protocol detected early asymptomatic root infections and distinguished significant differences in the level of resistance of 12 chickpea cultivars that grew in that same field plot infested with several races of the pathogen. Use of this protocol for fast, reliable, and cost-effective quantification of F. oxysporum f. sp. ciceris in asymptomatic chickpea tissues at early stages of the infection process can be of great value for chickpea breeders and for epidemiological studies in growth chambers, greenhouses and field-scale plots.