The effect of fumigants on soil recolonization in the glasshouse by organisms colonizing the spermosphere

Germinating turnip seeds were used as baits to measure changes in colonizing floras of the spermosphere in glasshouse soil boxes following fumigation. The spermosphere mycoflora of the untreated soil was always dominated by Fusarium, Pythium, and Gliocladium spp. Methyl bromide, chloropicrin, and MBC₃₃ (a 67:33 mixture of methyl bromide and chloropicrin), applied in polyethylene bags at a rate of 2·5 ml/cubic foot of soil, greatly reduced colonization by Fusarium and Pythium spp. for 120 days. Fungi and actinomycetes recolonizing treated soils were more active than in untreated soils, and each fumigant induced a characteristic recolonization pattern. The spermosphere of methyl bromide-treated soil was initially dominated by actinomycetes and later by Penicillium spp. In chloropicrin-treated soil, Trichoderma and later Penicillium spp. dominated, and in soil treated with MBC ₃₃, Penicillium and Trichoderma spp. were co-dominant. Dilution plates, made at the same time from the same soil, indicated a close correlation between inoculum density of different fungi in the soil and their inoculum potentials towards the spermosphere.     

Cost-effectiveness of five burrow fumigants for managing black-tailed prairie dogs

We evaluated the cost-effectiveness of two solid form burrow fumigants (aluminum phosphide and gas cartridges) and three pressurized gas–liquid burrow fumigants (methyl bromide, chloropicrin, and a methyl bromide–chloropicrin mixture) for managing black-tailed prairie dogs (Cynomys ludovicianus). Fifty-two variable-sized plots, including 25 treatment and 25 control burrows, were established within 13 prairie dog colonies in central Nebraska during spring 1989. Each group of 25 treatment burrows was fumigated with one of the five fumigants according to label directions or manufacturer recommendations. All five fumigants reduced burrow activity 95–98%, as measured by a plugged burrow technique. No significant differences in efficacy (P=0.453) were detected among the five treatments. Total costs for materials and labor for the aluminum phosphide and gas cartridges, excluding application equipment, were twice ($75.00 to $96.88 ha⁻¹) the cost of the pressurized gas–liquid fumigants ($37.67 to $41.76 ha⁻¹). Costs for the application equipment were considerably higher for the pressurized materials. Each treatment required labor for burrow plugging, which accounted for 50–75% of the total cost. None of the products tested met all requirements of a proposed selection criteria for fumigants.     

Chemical Control of Nematodes and Soil-borne Plant-Pathogenic Fungi on Cabbage Tranplants

Six general-purpose fumigants and one fungicide were applied by different methods and evaluated for control of nematode-fungus complexes on cabbage grown for transplant production. All chemicals reduced populations of nematodes and soil-borne fungi but varied greatly in effectiveness. Methyl bromide + chloropicrin (98% methyl bromide + 2% chloropicrin) (MBR-CP gas), DD + methyl isothiocyanate (DD-MENCS), methyl bromide + chloropicrin (67% methyl bromide + 31.75% cbloropicrin) (MBR-CP gel), and chloropicrin were more effective than sodium methyl dithiocarbamate (metham), pentachloronitrobenzene (PCNB), and potassium N-hydroxy-methyl-N-methyldithiocarbamate (Bunema) against Meloidogyne incognita. Populations of Pythium spp. and Fusarium spp. were reduced markedly by all treatments except PCNB. Plant growth, uniformity, and yield were greater when nematodes and fungi were controlled.     

Impact of fumigants on soil microbial communities.

Agricultural soils are typically fumigated to provide effective control of nematodes, soilborne pathogens, and weeds in preparation for planting of high-value cash crops. The ability of soil microbial communities to recover after treatment with fumigants was examined using culture-dependent (Biolog) and culture-independent (phospholipid fatty acid [PLFA] analysis and denaturing gradient gel electrophoresis [DGGE] of 16S ribosomal DNA [rDNA] fragments amplified directly from soil DNA) approaches. Changes in soil microbial community structure were examined in a microcosm experiment following the application of methyl bromide (MeBr), methyl isothiocyanate, 1,3-dichloropropene (1,3-D), and chloropicrin. Variations among Biolog fingerprints showed that the effect of MeBr on heterotrophic microbial activities was most severe in the first week and that thereafter the effects of MeBr and the other fumigants were expressed at much lower levels. The results of PLFA analysis demonstrated a community shift in all treatments to a community dominated by gram-positive bacterial biomass. Different 16S rDNA profiles from fumigated soils were quantified by analyzing the DGGE band patterns. The Shannon-Weaver index of diversity, H, was calculated for each fumigated soil sample. High diversity indices were maintained between the control soil and the fumigant-treated soils, except for MeBr (H decreased from 1.14 to 0.13). After 12 weeks of incubation, H increased to 0.73 in the MeBr-treated samples. Sequence analysis of clones generated from unique bands showed the presence of taxonomically unique clones that had emerged from the MeBr-treated samples and were dominated by clones closely related to Bacillus spp. and Heliothrix oregonensis. Variations in the data were much higher in the Biolog assay than in the PLFA and DGGE assays, suggesting a high sensitivity of PLFA analysis and DGGE in monitoring the effects of fumigants on soil community composition and structure. Our results indicate that MeBr has the greatest impact on soil microbial communities and that 1,3-D has the least impact.     

Impact of Fumigants on Soil Microbial Communities

Agricultural soils are typically fumigated to provide effective control of nematodes, soilborne pathogens, and weeds in preparation for planting of high-value cash crops. The ability of soil microbial communities to recover after treatment with fumigants was examined using culture-dependent (Biolog) and culture-independent (phospholipid fatty acid [PLFA] analysis and denaturing gradient gel electrophoresis [DGGE] of 16S ribosomal DNA [rDNA] fragments amplified directly from soil DNA) approaches. Changes in soil microbial community structure were examined in a microcosm experiment following the application of methyl bromide (MeBr), methyl isothiocyanate, 1,3-dichloropropene (1,3-D), and chloropicrin. Variations among Biolog fingerprints showed that the effect of MeBr on heterotrophic microbial activities was most severe in the first week and that thereafter the effects of MeBr and the other fumigants were expressed at much lower levels. The results of PLFA analysis demonstrated a community shift in all treatments to a community dominated by gram-positive bacterial biomass. Different 16S rDNA profiles from fumigated soils were quantified by analyzing the DGGE band patterns. The Shannon-Weaver index of diversity, H, was calculated for each fumigated soil sample. High diversity indices were maintained between the control soil and the fumigant-treated soils, except for MeBr (H decreased from 1.14 to 0.13). After 12 weeks of incubation, H increased to 0.73 in the MeBr-treated samples. Sequence analysis of clones generated from unique bands showed the presence of taxonomically unique clones that had emerged from the MeBr-treated samples and were dominated by clones closely related to Bacillus spp. and Heliothrix oregonensis. Variations in the data were much higher in the Biolog assay than in the PLFA and DGGE assays, suggesting a high sensitivity of PLFA analysis and DGGE in monitoring the effects of fumigants on soil community composition and structure. Our results indicate that MeBr has the greatest impact on soil microbial communities and that 1,3-D has the least impact.     

INFLUENCE OF SUPPLEMENTAL INORGANIC NUTRIENTS ON GROWTH,SURVIVORSHIP, AND MYCORRHIZAL RELATIONSHIPS OF SCHIZACHYRIUM SCOPARIUM (POACEAE) GROWN IN FUMIGATED AND UNFUMIGATED SOIL

Little bluestem grass Schizachyrium scoparium ([Michx.] Nash) plants were grown under field conditions for 2 years in soils fumigated with methyl bromide and chloropicrin, or in unfumigated soil, and treated with supplemental inorganic nutrients (bases calcium and magnesium) phosphorus, nitrogen, and potassium. Most differences in measured plant responses were due to interactions between fumigation and nutrient treatments. These included biomass production, root mass per unit length (μg/cm), root lengths, flowering culm production, percent colonization, colonized root length, and spore production in rhizosphere soil. Plants generally responded to mycorrhizal fungal colonization by reducing total root length and producing thicker roots. Treatment of plants with bases appeared to profoundly affect the mycorrhizal association by reducing sporulation of vesicular-arbuscular mycorrhizal fungi and increasing colonization. When fumigated or unfumigated soils were considered separately, base-treated plants produced more biomass than other treatments. Base-treated plants grown on unfumigated soil had more flowering culms and longer colonized root lengths than all other plants. Percent colonization by mycorrhizal fungi and colonized root length were positively correlated with phosphorus/nitrogen ratios, but the ratio was not correlated with plant biomass production. This suggests that phosphorus is not a limiting nutrient in our soil and investment in a mycorrhizal association may not result in enhanced plant growth. The base-nutrient effects may indicate a need to reevaluate earlier studies of macro nutrient effects that did not take into account the role played by calcium and magnesium in assessing fungus-host plant interactions.     

Bacterial Oxidation of Methyl Bromide in Fumigated Agricultural Soils

The oxidation of [(sup14)C]methyl bromide ([(sup14)C]MeBr) to (sup14)CO(inf2) was measured in field experiments with soils collected from two strawberry plots fumigated with mixtures of MeBr and chloropicrin (CCl(inf3)NO(inf2)). Although these fumigants are considered potent biocides, we found that the highest rates of MeBr oxidation occurred 1 to 2 days after injection when the fields were tarped, rather than before or several days after injection. No oxidation of MeBr occurred in heat-killed soils, indicating that microbes were the causative agents of the oxidation. Degradation of MeBr by chemical and/or biological processes accounted for 20 to 50% of the loss of MeBr during fumigation, with evasion to the atmosphere inferred to comprise the remainder. In laboratory incubations, complete removal of [(sup14)C]MeBr occurred within a few days, with 47 to 67% of the added MeBr oxidized to (sup14)CO(inf2) and the remainder of counts associated with the solid phase. Chloropicrin inhibited the oxidation of MeBr, implying that use of this substance constrains the extent of microbial degradation of MeBr during fumigation. Oxidation was by direct bacterial attack of MeBr and not of methanol, a product of the chemical hydrolysis of MeBr. Neither nitrifying nor methane-oxidizing bacteria were sufficiently active in these soils to account for the observed oxidation of MeBr, nor could the microbial degradation of MeBr be linked to cooxidation with exogenously supplied electron donors. However, repeated addition of MeBr to live soils resulted in higher rates of its removal, suggesting that soil bacteria used MeBr as an electron donor for growth. To support this interpretation, we isolated a gram-negative, aerobic bacterium from these soils which grew with MeBr as a sole source of carbon and energy.     

Changes in microorganisms populations in the soil after fumigation

Soil fumigation with dazomet, metam sodium, chloropicrin and chloropicrin + 1.3 D resulted in significant decrease of fungi and increase of bacteria populations in trials carried out in four farms located in different areas. Depending on the farm and the active substance applied, the fungi population was decreased by 1.4- to 3500-fold in comparison to control. Metam sodium and chloropicrin showed the best efficacy, both of them almost totally eliminated the fungi from the soil environment.The total number of bacteria was increased by the chemical fumigation with all tested products. While the population of fluorescent Pseudomonads in all treated plots increased from 2- to 100-fold, depending on the farm, the number of Bacillus spp. was not changed or decreased compared with non fumigated soil.The nematology analysis of the soil indicated that any chemical fumigant significantly limited the population of plant parasitic nematodes, which number was, anyway, below the damage threshold. However, in most cases dazomet and metam sodium reduced the total number of all nematodes present in the soil.The fumigation with chloropicrin and 1,3 D at dose of 30 g/m2 resulted in an increase of the total number of all nematodes in soil.     

Soil fumigation with methyl bromide: bromide accumulation by lettuce plants

Lettuce plants grown in beds of soil previously fumigated with methyl bromide accumulated water-extractable bromide, the amount present in the tissues depending on the concentration of inorganic bromide produced in the soil by the breakdown of the fumigant. Samples of lettuce plants from commercial nursery soils fumigated with methyl bromide at rates of 1–2 lb/ 100 ft² (49–98 g/m²) gave rise to soil bromide levels of n-6i/μg/g. The corresponding bromide concentrations in the plants ranged from i-6 to io-1 mg/g of dry tissue. The bromide concentrations in whole lettuce plants grown in pots of soil supplemented with 0–5 mg/g inorganic bromide, as potassium bromide, ranged up to 100 mg/g of dry tissue. Bromide taken up from the soil by lettuce plants was located mainly in the outer leaves. Lettuce was relatively insensitive to the presence of bromide in the soil; no phytotoxic symptoms were observed in plants growing in soils containing 5 mg/g inorganic bromide. Implications in relation to possible tolerance limits for the bromide content of lettuce plants are discussed.     

Root-Knot Nematode Management in Double-Cropped Plasticulture Vegetables

Combination treatments of chisel-injected fumigants (methyl bromide, 1,3-D, metam sodium, and chloropicrin) on a first crop, followed by drip-applied fumigants (metam sodium and 1,3-D ± chloropicrin) on a second crop, with and without oxamyl drip applications were evaluated for control of Meloidogyne incognita in three different tests (2002 to 2004) in Tifton, GA. First crops were eggplant or tomato, and second crops were cantaloupe, squash, or jalapeno pepper. Double-cropped vegetables suffered much greater root-knot nematode (RKN) pressure than first crops, and almost-total yield loss occurred when second crops received no nematicide treatment. On a first crop of eggplant, all fumigants provided good nematode control and average yield increases of 10% to 15 %. On second crops, higher application rates and fumigant combinations (metam sodium and 1,3-D ± chloropicrin) improved RKN control and increased yields on average by 20% to 35 % compared to the nonfumigated control. Oxamyl increased yields of the first crop in 2003 on average by 10% to 15% but had no effect in 2004 when RKN failed to establish itself. On double-cropped squash in 2003, oxamyl following fumigation provided significant additional reduction in nematode infection and increased squash yields on average by 30% to 75%.     

Linking Soil Biotic and Abiotic Factors to Apple Replant Disease: a Greenhouse Approach

Apple replant disease (ARD) is a frequently occurring plant disease, which causes retarded growth and mortality of young apple trees in replanted orchards. The aetiology is not well understood, but soil‐borne micro‐organisms are often discussed as primary causal agents of the replant problem. A greenhouse study was conducted in Laimburg, Italy, with orchard soils from the region, with the aim of obtaining information about the influence of soil biotic and abiotic factors on the aetiology of the disease. Apple rootstocks (M9) were planted into soils cultivated with apple trees that were either fumigated with chloropicrin or not fumigated, as well as mixtures of fumigated and non‐fumigated soils. In addition, uncultivated soils (from the inter‐row, from a fallow plot and from a meadow) were taken as controls. Various parameters were measured after 62 days in a controlled pot assay. Soils fumigated with chloropicrin resulted in higher apple shoot growth and lower microbial biomass carbon than non‐fumigated soils. Uncultivated soils had generally the highest microbial biomass carbon and the highest ergosterol contents. No considerable differences between basal respiration, ergosterol content, pH, electrical conductivity, and most nutrient and metal contents were observed between fumigated and non‐fumigated soils. Denaturing gradient gel electrophoresis gels of DNA extracted from the soils revealed differences in the fungal, bacterial and actinobacterial communities of the different soils, indicating significant shifts in microbial community composition after chloropicrin treatment. This study indicates biotic factors in soil to be a causal agent of apple replant disease.     

有机物料厌氧发酵液中拮抗苹果再植障碍病原真菌的细菌筛选及其防治效果

有机物料厌氧发酵液(AFOF)能显著改善苹果再植障碍.本研究对AFOF中能拮抗苹果再植障碍主要病原菌(腐皮镰刀菌、层出镰刀菌、尖孢镰刀菌、串珠镰刀菌)的细菌进行了分离筛选,并对其作用效果进行了盆栽验证.结果表明: AFOF能显著抑制病原真菌的生长繁殖;对峙试验共得到4株具有较强拮抗作用的细菌(L11、L12、L13、L14),最高抑菌率达到57.3%,鉴定发现这4株细菌均属于芽孢杆菌属,相互之间没有明显的拮抗作用;在盆栽条件下,与连作土相比,溴甲烷熏蒸处理和拮抗菌菌液处理对平邑甜茶幼苗的生物量均有不同程度的促进作用;在幼苗的长势上,溴甲烷熏蒸处理效果要好于拮抗菌菌液处理;在根系活力上,拮抗菌菌液处理效果要好于溴甲烷熏蒸处理,根系长度、根尖数分别增加了25.1%、70.9%.与连作土处理相比,拮抗菌菌液和溴甲烷熏蒸均能显著降低土壤中的真菌数量,分别降低了71.2%和64.2%,拮抗菌菌液处理能显著增加土壤中的细菌和放线菌数量,分别增加了48.0%和140.2%,使土壤微生物结构向“细菌型”转化;而溴甲烷熏蒸处理显著降低了土壤中的细菌和放线菌数量,说明拮抗菌的确能够抑制土壤中病原真菌的生长.     

Effect of soil fumigants on Fusarium wilt and nodulation of peas (Pisum sativum L.)

Chloropicrin, dazomet, formaldehyde, and D-D soil treatments all decreased the incidence of Fusarium wilt in a wilt-susceptible variety of pea grown in wilt-infested soil, but only chloropicrin and dazomet gave satisfactory control of the disease. All four fumigants decreased root nodulation, but no adverse effects on plant growth were detected. With dazomet, formaldehyde, and D-D, decreased nodulation is largely attributed to the extra soil nitrogen mineralized, whereas with chloropicrin the almost complete suppression of nodulation probably reflects the lethal effect of this material on the Rhizobium bacteria.     

The effect of DD nematocide on soil micro-organisms

The application of DD, a 1∶1 mixture of 1,3-dichloropropene and 1,2-dichloropropane, at field rate, to soil had neither stimulatory nor suppressive effects on bacteria, actinomycetes, fungi and cellulose decomposing bacteria. The toxic effect of the nematocide onAzotobacter and nitrogen-fixing clostridia was slight, the organisms recovering in a very short time. In fumigated soils the counts ofNitrosomonas andNitrobacter were markedly reduced and remained lower than the counts in the untreated soils for the 30 days duration of the experiment. The inhibitory effects of DD were to some extent influenced by soil type, being most marked in sandy and loam and least in calcareous soils.     

Biodegradation of Halogenated Hydrocarbon Fumigants by Nitrifying Bacteria

Three species of nitrifying bacteria were tested for the ability to degrade the halocarbon fumigants methyl bromide, 1,2-dichloropropane, and 1,2-dibromo-3-chloropropane. The soil nitrifiers Nitrosomonas europaea and Nitrosolobus multiformis degraded all three fumigants, while the marine nitrifier Nitrosococcus oceanus degraded only methyl bromide under the conditions tested. Inhibition of biodegradation by allylthiourea and acetylene, specific inhibitors of ammonia monooxygenase, suggests that ammonia monooxygenase is the enzyme which catalyzes fumigant degradation.     

Chemical control of root disease of Douglas–fir seedlings in relation to fungus and nematode populations

Seed treatment with thiram reduced post–emergence damping–off, while fumigating forest nursery soils with methyl bromide or DD improved Douglas-fir seedling emergence, shoot and root growth, and decreased the incidence of root disease. At an old site, where corky root develops, the benefits from these fumigants were associated with fewer (a) Xiphinema bakeri and (b) isolates of Cylindrocarpon radicicola. At a new site, decrease in Fusarium root rot and increase in shoot growth were related to reduction of populations of Paratylenchus and Pratylenchus, respectively. In unfumigated soils, Fusarium oxysporum was isolated from diseased and healthy roots.     

Ectomycorrhizal fungi: A new source of atmospheric methyl halides?

Incomplete source budgets for methyl halides – compounds that release inorganic chlorine and bromine radicals which, in turn, catalyze atmospheric ozone depletion – limit our ability to predict the fate of the stratospheric ozone layer. We report here the first measured emissions of methyl chloride, methyl bromide, and methyl iodide from ectomycorrhizal fungi. We grew nine fungal isolates on growth media containing halide concentrations similar to those found in soils and plant tissues. The observed range of emissions was 0.003–65 μg methyl chloride, 0.001–3 μg methyl bromide, and 0.02–12 μg methyl iodide g^?1 dry weight fungi day^?1. Species varied in production rates of methyl chloride vs. methyl bromide vs. methyl iodide. Cenococcum geophilum, a widespread ectomycorrhizal fungus, was further tested to investigate the effects of halide substrate concentration in growth media. Emissions from this species increased linearly with increasing concentrations of both bromide and iodide. In addition, a subset of four fungi was studied with two media concentrations each of chloride, bromide, and iodide (0.2 or 20 mm ). These fungi had similar responses to halide concentration, despite 1000‐fold differences in baseline emission rates between isolates. Finally, high chloride concentrations (20 mm ) in media did not appear to inhibit emissions of methyl bromide or methyl iodide. Overall, ectomycorrhizal fungi might be an important source of methyl halides to the atmosphere, and substrate concentrations and community composition may influence production levels in ecosystems.     

Effects of zinc-smelter emissions on forest soil microflora.

Within 2 km of a zinc (Zn) smelter in Palmerton, Pennsylvania, near the Lehigh Water Gap, up to 13.5% Zn by weight has been measured in the O2 horizon of the soil, and up to 8% Zn in the A1 horizon. The total numbers of bacteria, actinomycetes, and fungi (measured by dilution plate counts) were greatly reduced in the most severely Zn-contaminated soils compared with control soils. The reduction of microbial populations may be a partial cause of the decreased rate of litter decomposition at Lehigh Gap. Growth of most bacteria from control sites was reduced by 100 to 200 muM Zn, most actinomycetes by 100 muM Zn, and most fungi by 100 to 1000 muM Zn in thin-Pablum extract agar (TPab). All the tested actinomycetes and non-spore-forming bacteria isolated from Zn-contaminated Lehigh Gap soils were Zn-tolerant, growing normally in media containing 600-2000 muM Zn. Most fungi, regardless of source, were capable of at least 50% of normal growth at 700 muM Zn. Zinc-tolerant bacteria, actinomycetes, and fungi were readily isolated from low-Zn soils, suggesting that selection for Zn tolerance may proceed rapidly. Acidophilic Mortierella species have been selectively eliminated near the smelter, apparently because of elevated soil pH. Peryronellaea glomerata (Corda) Goidanich and Coniothyrium spp. were found only in the high-Zn soils.     

Field Released Transgenic Papaya Affects Microbial Communities and Enzyme Activities in Soil

Soil properties, microbial communities, and enzyme activities were studied in soil planted with transgenic or nontransgenic papaya under field conditions. The transgenic papaya contained a replicase (RP) mutant gene of the papaya ringspot virus (PRSV), which conferred resistance to the virus, the neomycin phosphotransferase II (NPT II) marker gene, which conferred Km resistance, and a cauliflower mosaic virus 35S promoter (CaMV 35S). There were significant differences (P < 0.05) in the total number of colony forming units (CFUs) of bacteria, actinomycetes, and fungi between soils planted with RP-transgenic and nontransgenic plants; total CFUs of bacteria, actinomycetes, and fungi in soil planted with transgenic papaya were significantly higher by 0.43, 0.80, and 0.46 times, respectively. Significantly higher (P < 0.05) CFUs of bacteria, actinomycetes, and fungi resistant to kanamycin (Km) were present in soils planted with the transgenic papaya than in those planted with nontransgenic papaya. Resistance quotients (CFU in the presence of a chemical relative to that without) of Km-resistant bacteria, actinomycetes and fungi were higher in soil planted with transgenic papaya, and the resistance quotients of Km-resistant bacteria, actinomycetes, and fungi in soils planted with transgenic papaya increased statistically significantly (P<0.05) from 1.5 to 2.5, from 1.2 to 2.6, and from 0.9 to 2.8 times, respectively. Soils planted with transgenic papaya had significantly higher enzyme activities of arylsulfatases (+5.4 times), alkaline phosphatases (+0.5 time), invertase (+0.5 time) and phosphodiesterases (+0.2 time), but lower enzyme activities of proteases (−2.1 times), polyphenol oxidases (−1.4 times), urease (−0.2 time) than the soils planted with nontransgenic papaya. Our results suggest that transgenic papaya could alter chemical properties, enzyme activities, and microbial communities in soil.     

Survival of Escherichia coli O157:H7 in soil and on lettuce after soil fumigation

Long-term survival of Escherichia coli O157:H7 in soil and in the rhizosphere of many crops after fumigation is relatively unknown. One of the critical concerns with food safety is the transfer of pathogens from contaminated soil to the edible portion of the plants. Multiplex fluorogenic polymerase chain reaction was used in conjunction with plate counts to quantify the survival of E. coli O157:H7 in soil after fumigation with methyl bromide and methyl iodide in growth chamber and microcosm laboratory experiments. Plants were grown at 20 degrees C in growth chambers during the first experiment and soils were irrigated with water contaminated with E. coli O157:H7. For the second experiment, soil microcosms were used in the laboratory without plants and were inoculated with E. coli O157:H7 and spiked with the two fumigants. Primers and probes were designed to amplify and quantify the Shiga-like toxin 1 (stx1) and 2 (stx2) genes and the intimin (eae) gene of E. coli O157:H7. Both fumigants were effective in reducing pathogen concentrations in soil, and when fumigated soils were compared with nonfumigated soils, pathogen concentrations were significantly higher in the nonfumigated soils throughout the study. This resulted in a longer survival of the pathogen on the leaf surface especially in sandy soil than observed in fumigated soils. Therefore, application of fumigant may play some roles in reducing the transfer of E. coli O157:H7 from soil to leaf. Regression models showed that survival of the pathogen in the growth chamber study followed a linear model while that of the microcosm followed a curvilinear model, suggesting long-term survival of the pathogen in soil. Both experiments showed that E. coli O157:H7 can survive in the environment for a long period of time, even under harsh conditions, and the pathogen can survive in soil for more than 90 days. This provides a very significant pathway for pathogen recontamination in the environment.