1,3-dichloropropene distribution in soil when applied by drip irrigation or injection in pineapple culture

The fumigant nematicide, 1,3-dichloropropene (1,3-D VL; ‘Telone’ II) and a soluble liquid formulation, 1,3-D SL were tested in a pineapple field experiment to evaluate the vapor movement of the two formulations in soil gas as well as the movement and persistence of 1,3-D SL in soil profiles. Prior to planting, 1,3-D VL (407 kg ha^?1) was hand-injected into the soil in two parallel rows per planting bed to approximate the practice of chisel injection. 1,3-D SL (407 kg ha^?1) was applied with 6 mm of water by drip irrigation through a drip tube in the center of the bed. Post-plant applications of 1,3-D SL (113 kg ha^?1) were made at three-month intervals during a two-crop cycle. 1,3-D concentrations in soil gas were lower at the plant line in the drip treatment compared with the 1,3-D VL treatment, owing to differences in application method and fumigant placement. 1,3-D in the vapor phase reached peak concentrations 24 h after injection in the 1,3-D VL treatment compared with a peak at 48 h in the drip treatment. Post-plant applications of 1,3-D SL resulted in a three-fold difference in peak 1,3-D soil gas concentrations between replicate applications, the concentration being inversely related to soil moisture at the time of sampling. Drip application of 1,3-D SL resulted in a relatively uniform distribution of 1,3-D across the bed and to a depth of 45 cm. There was no effect of formulation on downward movement of 1,3-D and persistence in soil profiles sampled two weeks and one month after application. Rainfall which occurred 9 days after pre-plant 1,3-D fumigation resulted in leaching of 1,3-D to a depth of 150 cm in soil profiles. Due to the short half-life of 1,3-D, significant penetration of 1,3-D in the soil was observed only when irrigation or rainfall occurred soon after application.     

Effect of application timing and method on efficacy and phytotoxicity of 1,3-D, chloropicrin and metam-sodium combinations in squash plasticulture

BACKGROUND: Metam-sodium, 1,3-dichloropropene (1,3-D) and chloropicrin are widely used soil fumigants. Combined application of metam-sodium and 1,3-D + chloropicrin is intended to improve efficacy and broaden spectrum of control, but little is known about the effect on crop safety. This study aimed to evaluate the effects of application timing of fumigant combinations on soilborne pest and disease control (nematodes, soil fungi and weeds) and growth of squash. Two separate tests with chisel-injected and drip-applied fumigant combinations and plant-back times ranging from 1 to 4 weeks were conducted in Tifton, GA, USA, in spring and fall 2002. RESULTS: Fumigant combinations using 1,3-D, chloropicrin and metam-sodium were as effective as methyl bromide in controlling Meloidogyne incognita (Kofoid & White) Chitwood, Pythium irregulare Buis., Rhizoctonia solani Kühn and Cyperus esculentus L. Chisel-applied combinations were more effective in terms of root-knot nematode control than drip-applied combinations. Root-knot nematode reduced squash yields by up to 60%. Phytotoxicity problems and lower yields were observed during spring, especially following 1,3-D + chloropicrin and when plant-back periods were shorter. CONCLUSION: The main problem with fumigant alternatives to methyl bromide may not be reduced efficacy but, in particular for 1,3-D products, loss of flexibility in terms of longer plant-back periods.     

Fumigant combinations for Cyperus esculentum L control

The phase-out of methyl bromide as a soil fumigant has stimulated research into the use of other soil fumigants for weed control. Methyl bromide, methyl iodide, propargyl bromide, 1,3-dichloropropene (1,3-D) and metam-sodium were tested alone and in combination with chloropicrin in laboratory experiments to determine their efficacy against Cyperus esculentus L (yellow nutsedge) tubers. Propargyl bromide and metam-sodium were the most efficacious fumigants tested, with EC50 values of 3.7 and 6.5 microM, respectively. The relative potencies of methyl iodide and chloropicrin were not significantly different but were 2.6 and 2.9 times more potent than methyl bromide, respectively. The EC50 values for all fumigants other than 1,3-D were significantly lower than that of methyl bromide. Combining each fumigant with 17% chloropicrin resulted in a synergistic interaction. The greatest increase in potency between the expected result and the actual result was a relative potency of 3.8 with the methyl bromide/chloropicrin combination. The smallest increase in efficacy was with propargyl bromide and chloropicrin, with a relative potency of 1.5. There was no significant difference between the EC50 values of methyl bromide/chloropicrin and methyl iodide/chloropicrin combinations. Combining 1,3-D with 17% chloropicrin resulted in an EC50 value for C. esculentus control similar to that of methyl iodide applied alone.     

Spatial and temporal distributions of 1,3-dichloropropene in soil under drip and shank application and implications for pest control efficacy using concentration–time index

A field experiment was conducted to study the spatial and temporal distributions of (EZ)-1,3-dichloropropene (1,3-D) in the soil and effects on pest control efficacy. An emulsifiable concentrate formulation of 1,3-D (Telone EC) was applied with drip irrigation at 47 kg AI ha⁻¹ to two different depths (2.5 and 20.3 cm, respectively). Comparisons were made between the two drip treatments and a direct shank injection of 1,3-D (Telone II) at 112 kg AI ha⁻¹. Concentrations of 1,3-D in soil air were measured at several locations over time to determine the spatial and temporal characteristics, and to calculate the concentration–time index (CT). Citrus nematodes (Tylenchulus semipenetrans) were placed in the fumigated soil at 25 cm depth and their mortality rates were compared to the calculated CT. Distributions of 1,3-D were found to be relatively uniform in both the drip irrigation and the shank injection treatment. An application rate of 47 kg ha⁻¹ with drip irrigation was sufficient to achieve significant concentration levels in soil beds. Applying 1,3-D with direct shank injection at 112 kg ha⁻¹ extended the measurable concentration levels to the furrows between the soil beds and to a depth of 1 m below the soil surface. Effective control of T. semipenetrans was achieved with both the drip irrigation and the shank injection. A threshold soil 1,3-D CT value of 12 μg h cm⁻³ was needed to reach a 100% efficacy for T. semipenetrans. The study indicates that 1,3-D fumigation may be carried out with drip irrigation at very low rate, and a CT index may be derived to aid in the determination of a minimum effective dosage. © 1999 Society of Chemical Industry     

Incompatibility of metam sodium with halogenated fumigants

Metam sodium (metam) is a widely used soil fumigant. Combined application of metam and other available fumigants is intended to produce synergic pesticidal effects for a broad spectrum of pest control in soil fumigation. This study aimed to test the compatibility of metam with the halogenated fumigants 1,3-dichloropropene (1,3-D), chloropicrin, methyl bromide, methyl iodide and propargyl bromide. Halogenated fumigants and metam were spiked simultaneously into organic solvents, water and moist soils, and metam-induced degradation of these halogenated chemicals was evaluated. In all three media, the halogenated fumigants were incompatible with metam and degraded via rapid chemical reactions. The degradation rate varied with halogenated fumigant species and increased as the amount of metam present was increased. In moist soil, 15-95% of the halogenated fumigants were decomposed within 72 h by metam at a 1:1 molar ratio. Combined application of Telone C-35 (62.5% 1,3-D + 35% chloropicrin) at 265 mg kg(-1) and Vapam (42% metam) at 567 mg kg(-1) in soil resulted in complete disappearance of the applied chloropicrin and 20-38% of the 1,3-D within 8 h. The results suggest that simultaneous application of halogenated fumigants and metam at the same soil depth will not maximize pest control. In practice, sequential treatment of soil or application at different soil depths is recommended when these two types of fumigants are used in combination.     

Dye injection for predicting pesticide movement in micro-irrigated polyethylene film mulch beds

A new method is described for tracing water movement in polyethylene film covered soil beds. Dye was delivered via a drip tape micro-irrigation system which was placed in the bed as the soil beds were shaped and covered with polyethylene film. The dye was injected into the system and irrigated with water for 4-24 h at 0.41-1.38 bar (41-138 kPa) pressure depending on the experiment. The dye appeared as blue circles on the soil surface within 20 min of injection and produced a three-dimensional pattern in the soil profile. Injection-irrigation-pressure scenarios were evaluated by measuring dye movement directly below and between emitters by sliding fabricated blades vertically into the bed at the desired examination point and excavating the soil away from the blade. The dye typically produced a U shape on the face of the bed and the area was calculated for each of these exposed faces. The area increased as the length of irrigation and water pressure increased. Interrupted irrigation (pulsing) scenarios did not alter the calculated areas encompassed by the dye compared to uninterrupted irrigation scenarios. The blue dye provided a direct, inexpensive and easy method of visualizing water movement in soil beds. This information will be used to optimize application of emulsifiable plant-care products in polyethylene film mulch beds.     

Evaluation of chemical and integrated strategies as alternatives to methyl bromide for the control of root-knot nematodes in Greece

Current environmental awareness has led to a greater demand for alternative nematode control strategies. Three field experiments were established to compare management tactics on cucumber in commercial greenhouses naturally infested with root-knot nematodes (Meloidogyne spp). Cucumber rootstocks which have shown resistance to soil-borne diseases were tested to reveal any resistance/tolerance to root-knot nematodes, and integration of these rootstocks with nematicides was investigated. Metham-sodium and 1,3-dichloropropene (1,3-D) provided good control of nematode populations when their application was followed by the application of a non-fumigant nematicide such as cadusafos or oxamyl. Neither fumigant could provide season-long control of nematode populations, and a further application of cadusafos was required for satisfactory control. The efficacy of metham-sodium was significantly increased when injected into soil in comparison with its application through the drip irrigation system. The use of rootstocks resistant to soil-borne fungal pathogens used together with chemical means of nematode control provided promising results for their further use in integrated strategies as alternatives to methyl bromide. However, the latter was the superior treatment for the control of root-knot nematodes in soil infested with residues of galled roots. Dazomet, metham-sodium nor the non-fumigant nematicides oxamyl and fenamiphos could reduce nematode population as efficiently as methyl bromide. None of the chemicals tested except methyl bromide could enter galled roots and kill surviving nematodes.     

Subsurface drip application of alternative fumigants to methyl bromide for controlling nematodes in replanted grapevines

BACKGROUND: Many California grape growers use preplant fumigation to ensure uniform and healthy grapevine establishment in replant situations. A field study was conducted to evaluate the performance of subsurface drip‐applied chemical alternatives to methyl bromide on plant‐parasitic nematodes, plant vigor and fruit yield during the 6 year period following replanting. RESULTS: Subsurface drip fumigation with 1,3‐dichloropropene plus chloropicrin and with iodomethane plus chloropicrin had generally similar nematicide activity as methyl bromide in three grape types, while sodium azide was less effective. The combination of 1,3‐dichloropropene plus chloropicrin enhanced vine vigor similarly to methyl bromide. However, all plots treated with alternative fumigants produced less fruit yield than methyl bromide over the 4 years of evaluation. CONCLUSION: Subsurface drip fumigation with alternative chemicals to methyl bromide generally provided adequate management of plant‐parasitic nematodes during the vine establishment period. However, further research is required to increase the performance of alternative chemicals against other components of the replant problem, as grape yield in vines grown in the alternative treatments was lower than in methyl bromide. Copyright © 2011 Society of Chemical Industry     

Distribution and efficacy of drip-applied metam-sodium against the survival of Rhizoctonia solani and yellow nutsedge in plastic-mulched sandy soil beds

The effects of metam-sodium application rate on soil residence time, spatial and temporal distributions of methyl isothiocyanate and pest control efficacy were studied in a Georgia sandy soil. Metam-sodium 420 g L(-1) SL was drip applied at rates of 147 and 295 L ha(-1) in plastic-mulched raised beds. Methyl isothiocyanate concentrations in soil air space were monitored from four preselected sites: 10 and 20 cm below the emitter, and 20 and 30 cm laterally away from the emitter at 3, 12, 24, 48, 72, 120 and 240 h after chemigation. A higher rate of metam-sodium application resulted in higher methyl isothiocyanate concentrations in the soil. Highest methyl isothiocyanate concentrations were found at 20 cm below the emitter, and lowest at 30 cm laterally away from the emitter. Methyl isothiocyanate concentrations decreased with time and distance from the emitter. Lower methyl isothiocyanate concentration x time product values at 20 and 30 cm away from the emitter resulted in lower mortalities of Rhizoctonia solani Kühn and yellow nutsedge (Cyperus esculentus L.). The results demonstrated that methyl isothiocyanate can be delivered at lethal doses with drip-applied water downward within the beds. Lateral diffusion of methyl isothiocyanate from the point of application did not reach biologically active concentrations to affect the survival of R. solani or yellow nutsedge. Further studies on the lateral distribution of methyl isothiocyanate in sandy soils are needed to circumvent this limitation.     

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.     

完全不渗透膜对熏蒸剂大气散发的控制效果

为明确完全不透性膜(totally impermeable film,TIF)对熏蒸剂在田间应用时散发和残留的影响,采用静态散发箱技术测定了TIF与聚乙烯膜(polythene film,PE)对氯化苦、1,3-二氯丙烯(1,3-dichloropropene,1,3-D)和棉隆施用后所产生的异硫氰酸甲酯(methyl isothiocyanate,MITC)大气散发的控制效果,并应用气相色谱法检测了揭膜后3种熏蒸剂在土壤中的残留情况。结果表明,在20 g/m~2(棉隆为15 g/m~2)剂量下,氯化苦、1,3-D及MITC透过PE的累积散发率为施用量的6.42%、7.37%和22.27%,透过TIF的累积散发率为施用量的0、0.65%和2.05%,表明TIF极大地降低了熏蒸剂向大气的散发量,可有效控制熏蒸剂向大气扩散。揭膜后氯化苦及1,3-D在各处理土壤中的残留量均低于0.30 mg/kg,说明TIF没有增加土壤中氯化苦和1,3-D的残留量;但MITC(15 g/m~2)在TIF下10~20 cm土壤中的残留量在3.28~3.41 mg/kg之间,高于在PE下的残留量(0.46~0.47 mg/kg),表明TIF能提高MITC在土壤中的持效浓度。     

A monitoring programme for 1,3-dichloropropene and metabolites in groundwater in five EU countries

BACKGROUND: 1,3 Dichloropropene (1,3-D) is a preplanting soil fumigant for the control of cyst and free-living nematodes and is currently undergoing a resubmission under Annex 1 listing of Directive 91/414/EEC. The characteristics of 1,3-D are such that the risk of it or its soil metabolites leaching through the soil profile cannot be excluded. As such, groundwater monitoring programmes were established in five EU countries representing a wide range of agricultural, climatic and hydrogeological situations, covering a range of groundwater vulnerability scenarios. All monitoring was conducted in areas where there has been historical use of 1,3-D. RESULTS: Over 5000 groundwater samples were analysed for the presence of 1,3-D and its metabolites over a 2 year period. Almost all analyses (for parent and metabolites) yielded concentrations of <0.1 microg L(-1). There were just two detections of >0.1 microg L(-1) (0.12 microg L(-1) and 0.4 microg L(-1)) for the 3-chloroacrylic acid metabolite in shallow groundwater samples of the alluvial gravels of the River Tiétar in the Caceres region of Spain. CONCLUSION: Groundwater monitoring programmes have been conducted in the EU in five countries. These have demonstrated that there is negligible contamination of groundwater with 1,3-D or its metabolites across a range of agroclimatic regions where 1,3-D is known to have been used for a number of years. Local scientific knowledge of geological features, hydrology, agricultural practice and specific local issues was essential to the conduct of the study.     

Physical, chemical and environmental properties of selected chemical alternatives for the pre-plant use of methyl bromide as soil fumigant

Production and use of methyl bromide, a soil fumigant, are being restricted because of this chemical's deleterious effects on stratospheric ozone concentrations. Several products, some of which are currently used as soil fumigants, are being considered as possible replacements for methyl bromide, alone and in various combinations. Among these, 1,3-dichloropropene, methyl isothiocyanate generators such as metam-sodium, and chloropicrin are currently registered, while others such as methyl iodide and sodium azide are at different stages of the registration process. This review examines physicochemical properties, environmental fate, and metabolism of the various potential methyl bromide replacement products.     

Surface application of ammonium thiosulfate fertilizer to reduce volatilization of 1,3‐dichloropropene from soil

Atmospheric emission of the soil fumigant 1,3‐dichloropropene (1,3‐D) is of environmental concern because of its toxicity and carcinogenicity. Thiosulfate fertilizers have been found to rapidly transform 1,3‐D in soil to non‐volatile ions which are less toxic. We investigated the use of surface application of ammonium thiosulfate (ATS) for reducing 1,3‐D volatilization. In packed soil columns, emission of 1,3‐D applied by sub‐surface injection decreased with increasing ATS application rate and the amount of water used for delivering ATS. When ATS was applied in 9 mm water at 64 g m⁻², total 1,3‐D emission was reduced by 61%. The reduction was 89% when ATS was applied at 193 g m⁻². Bioassays showed that ATS application did not affect the effectiveness of 1,3‐D for controlling citrus nematodes. In field plots where a 1,3‐D emulsified formulation was applied via sub‐surface drip, surface spray of ATS reduced 1,3‐D emissions by 50%, and by 71% when the surface was also covered with polyethylene film. ATS application had no effect on the efficacy of root‐knot nematode control or tomato yields. These results suggest that surface application of thiosulfate fertilizers may be a feasible and effective strategy for minimizing 1,3‐D emissions. © 2000 Society of Chemical Industry     

Application of alternative fumigants through drip irrigation systems

ABSTRACT Strawberry fields in California (9,500 ha annually) are pre-plant fumigated with methyl bromide and chloropicrin to prevent serious soil pest and disease problems. Although soil fumigation with methyl bromide has ensured stability of strawberry production, its use is being discontinued because of its effect on stratospheric ozone. The likely short-term alternatives such as 1,3-dichloropropene, chloropicrin, and metham sodium, although not ozone depleters, are potentially hazardous to the environment and humans if applied improperly. Water-soluble formulations of alternative fumigants can be applied through drip irrigation systems established to irrigate crops. In comparison to conventional shank methods of injection, application of soluble formulations through drip irrigation systems would be economical and environmentally friendly, reduce worker exposure, and allow for simultaneous or sequential application of a combination of fumigants. This paper discusses techniques developed to apply alternative fumigants through drip irrigation systems, and reviews ongoing studies to determine optimum application rates, soil conditions, plastic mulches, and amount of irrigation water used to apply these alternative fumigants.     

Fumigation toxicity of volatile natural and synthetic cyanohydrins to stored-product pests and activity as soil fumigants

Insecticidal fumigation toxicity of natural and synthetic cyanohydrins was evaluated with four stored-product pests: the lesser grain borer, Rhyzopertha dominica (F), the red flour beetle, Tribolium castaneum Herbst, the saw-toothed grain beetle Oryzaephilus surinamensis L, the maize weevil, Sitophilus zeamais (Motsch) and the house fly, Musca domestica L. The fumigation LC50 values were calculated by probit analysis. For house flies, all but one of the cyanohydrins tested were more potent than 1,3-dichloropropene (Telone). Three were as efficacious as chloropicrin. For the lesser grain borer, all cyanohydrins tested were more insecticidal than dichloropropene, and all but one were more potent than chloropicrin. Four were as insecticidal as dichlorvos. The acetate of 1-cyano-1-hydroxy-2-propene (CHP-ace) was also tested in soil for antifungal and antibacterial activity, and inhibition of weed seed germination. CHP-ace reduced the total soil bacterial and fungal counts significantly, and was effective in inhibiting the germination of weed seeds in soil, indicating a broad spectrum of activity as a soil fumigant.     

Permeation of soil fumigants through agricultural plastic films

Plastic films are used in soil fumigation to control fumigant emission into the atmosphere. In previous studies it was shown that the plastic films are permeable to fumigant vapors. Virtually impermeable films (VIF) have been developed to reduce such emission and to increase the efficacy of pest control. A rapid, accurate, sensitive and simple method to measure the permeability of plastic films to soil fumigants that was developed in the present study is described in this paper. The method uses a static, closed system in which the tested film is fixed between two cells. The fumigant is sampled by a solid-phase microextraction method and measured quantitatively by gas chromatography. The method was used to assess the permeability of two plastic films — a low-density polyethylene film (LDPE) and a VIF — to commercial soil fumigants formulated individually or in mixtures. All the tested fumigants permeated through the commonly used LDPE film, in the following descending order of permeability: methyl isothiocyanate (MITC), methyl bromide (MBr), 1,3-dichloropropene (1,3-D; Telone), chloropicrin (CP). The VIF was impermeable to all the tested fumigants except MITC, the permeation of which was reduced by 40%. The permeation of some fumigants through LDPE films was influenced by the formulation used. The permeation of CP was increased when it was combined with MBr in Bromopic. With Telopic, a mixture of 1,3-D and CP, the permeation of 1,3-D through LDPE film was 62% greater than that of Telone, whereas that of CP was not affected. The permeation rates of both MBr and CP were 25–30% greater when they were formulated as a mixture in Bromopic than when they were formulated individually. The formulation of fumigants as mixtures of two components did not affect their permeability through VIF. This study showed that differences in the suitability of plastic films for soil fumigation can be measured easily in a laboratory. It also showed that the VIP was more effective than LDPE in reducing losses of fumigant to the atmosphere, thus allowing more efficient use of fumigants to manage soilborne pests. The presented method helps us to choose the most adequate film for optimizing fumigation efficacy, and reducing costs and environmental risks. http://www.phytoparasitica.org posting Sept. 17, 2006.     

Status of chemical alternatives to methyl bromide for pre-plant fumigation of soil

ABSTRACT None of the chemical alternatives currently registered and available has the full spectrum of activity and versatility of methyl bromide as a pre-plant soil fumigant. Chloropicrin and 1,3-dichloropropene (Telone) can provide significant control of many plant pathogens in soil and growth stimulation in annual crops. These compounds, however, provide limited control of weeds or other residual plant materials in soil of concern in nursery production systems, and some perennial replant diseases. Methyl isothiocyanate generators such as metam sodium have broad biocidal activity in soil, but are more difficult to apply effectively. In most soil applications, the available alternatives are likely to be used in combinations, either as mixtures (e.g., 1,3-dichloropropene and chloropicrin) or sequentially (e.g., chloropicrin followed by metam sodium). They may also be supplemented with other more specific pesticides and cultural controls. Among the alternatives currently under active development but not yet available, methyl iodide and propargyl bromide probably have activity that most closely parallels that of methyl bromide in soil. However, all of the chemical alternatives to methyl bromide will be subject to continuing review and more regulation. Furthermore, we do not know the actual prospects for registration of the new fumigants currently under development and there is a risk that registered fumigants will not be available for large-scale use in soil indefinitely.     

A simulation model for fate and transport of methyl bromide during fumigation in plastic‐mulched vegetable soil beds

A coupled water‐heat and chemical transport model was used to describe the fate and transport of methyl bromide fumigant in low‐density polyethylene plastic‐mulched soil beds used for vegetable production. Methyl bromide transport was described by convective‐dispersive processes including transformations through hydrolysis. Effects of non‐isothermal conditions on chemical transport were considered through inclusion of temperature effects on transport parameters. An energy‐balance approach was used to describe the plastic‐mulched boundary condition that controls the thermal regime within the soil bed. Simulations were made for variable water‐saturation regimes within the bed and for different depths of fumigant injection. Simulations for various scenarios revealed that large amounts (20–44% over a 7‐day period) of applied methyl bromide are lost from the un‐mulched furrows between the beds. Plastic mulching of the bed was found to be only partially effective (11–29% emission losses over a 7‐day period) in reducing atmospheric emissions. Deep injection of fumigant and saturating the soil with water both led to increased retention of methyl bromide within the soil and less emission to the atmosphere. However, deep injection was unfavorable for effective sterilization of the crop root zone. © 2000 Society of Chemical Industry     

气相色谱法测定蔬菜水果中的氯化苦残留

氯化苦土壤熏蒸是防治土传病害的有效措施。采用石油醚对蔬菜、水果样品进行超声波提取,以气相色谱电子捕获检测器测定氯化苦残留。结果表明,在浓度为0.008 ~2 mg/L范围内,线性相关系数r=0.999 4。氯化苦的添加浓度在0.02 ~1 mg/kg范围内,平均回收率为92.2% ~111%,相对标准偏差(RSD)为1.9% ~7.2%,均在农药残留测定允许范围内。该方法的最小检出量(LOD)为0.008 mg/kg,最低检测浓度(LOQ)为0.02 mg/kg。采用本方法对土壤熏蒸处理施用氯化苦后(PHI≥50 d)的甜瓜、草莓、大姜、茄子、菠菜收获期样品进行测定,均未检出氯化苦残留。