Application Of Fumigants Research Articles

Impact of repeated fumigant applications on soil properties, crop yield, and microbial communities in a plastic-mulched tomato production system

Pre-plant soil fumigation is widely applied to control nematodes, soil-borne fungal pathogens, and weeds in vegetable crops. However, most of the research evaluating the effect of fumigants on crop yield and soil microbial communities has been done on single compounds despite growers mainly applying fumigant combinations. We studied the effect of different fumigant combinations (chloropicrin, 1,3-dichloropropene, and metam potassium) on soil properties, crop yield, and the soil bacterial and fungal microbiome for two consecutive years in a plastic-mulched tomato production system in Florida (United States). While combinations of fumigants did not improve plant productivity more than the individual application of these products, application of fumigants with >60 % chloropicrin did significantly increase yield. Fumigant combinations had no significant effect on bacterial diversity, but fumigants with >35 % chloropicrin reduced soil fungal diversity and induced temporary changes in the soil bacterial and fungal community composition. These changes included short-term increases in the relative abundance of Firmicutes and Ascomycota, as well as decreases in other bacterial and fungal taxa. Repeated fumigation reduced network complexity and the relative abundance of several predicted bacterial functions and fungal guilds, particularly after fumigation and at end of harvest (3-months post fumigation). A structural equation model (SEM) showed fumigants not only directly impact crop yield, but they can also indirectly determine variations in plant productivity through effects on the soil microbiome. Overall, this study increases our understanding of the environmental and agricultural impacts of fumigants in a plastic-mulched tomato production system.

Residue behavior and efficacy of benzothiazole in grains under different fumigation conditions.

Benzothiazole was a potential grain fumigant for Tribolium castaneum. However, its safety profile and suitable fumigation conditions remain unknown. Therefore, we investigated the insecticidal efficacy, accumulation and dissipation of benzothiazole in grains (wheat, corn and rice) under different temperatures. WE ESTABLISHED A UNIVERSAL DETECTION METHOD (MODIFIED QUECHERS COUPLED WITH GC-MS/MS) OF BENZOTHIAZOLE RESIDUES IN THREE GRAINS, WHICH PROVIDING HIGH LINEARITY (R2 > 0.999), SENSITIVITY (LODS= 0.001 MG/KG, LOQS=0.002-0.005 MG/KG), ACCURACY (RECOVERIES = 88.18-118.75%) AND PRECISION (RSDS < 4.78%). THE INSECTICIDAL EFFICACY ORDER OF BENZOTHIAZOLE WAS 30 °C ≥ 10 °C > 20°C AND CORN > WHEAT > RICE. TEMPERATURE POSITIVELY AFFECTED THE ACCUMULATION/DISSIPATION RATE OF BENZOTHIAZOLE. RICE WAS THE MOST EASILY ACCUMULATED AND DISSIPATED GRAIN FOR BENZOTHIAZOLE RESIDUES, WHILE CORN ACCUMULATED BENZOTHIAZOLE MORE THAN WHEAT BUT LESS THAN RICE, WITH DISSIPATION SLOWER THAN WHEAT AND RICE.: CONCLUSION: Our results provide important references for the application of benzothiazole and even other fumigants. This article is protected by copyright. All rights reserved.

Efficacy of different chemical and non-chemical treatments for management of Galleria mellonella in stored combs

Bee keeping has also becoming popular as one of the components in mixed farming systems and source of income for small farmer or landless labourer and taken a shape of hopeful enterprise or business also. But due to attack of natural enemies especially Galleria mellonella on honey bees, the beekeeping industries suffers from huge losses. In present study to combat from the pest problems, microbial biopesticide, chemical and non-chemical methods have been tried widely against G. mellonella in stored combs. The research was carried out at Research farm, Apiary and Apiculture Laboratory of the Department of Entomology, Chaudhary Charan Singh Haryana Agricultural University, Hisar from June to December of both year 2016 and 2017. Among the different chemical and non-chemical measures tested for management of greater wax moth in stored combs; the most effective was storing stored comb at the low temperature treatment of -15 °C, -10 °C followed by at low temperature of -5 °C and 0 °C, Aluminum phosphide fumigation, Bt spray, separation of combs with newspapers, neem seed kernel extract (NSKE) spray, formic acid spray, acetic acid spray, hive chamber separation with newspaper, neem oil spray and broadcasting neem leaves powder. The study demonstrated the potentiality of low temperature treatment, Aluminum phosphide fumigation and Bt isolates against G. mellonella. Although, study also indicated that Aluminum phosphide fumigation in stored combs targets and destroy all life stages of the moth. Beside this, application of fumigants is economically convenient and requires little knowledge of the pest organism.

Alternative Management Strategies and Impact of the Northern Root-Knot Nematode in Daylily Production

Bare-root production of Hemerocallis spp., daylily, is of major economic importance to Michigan's ornamental industry, but production of clean nursery material is challenging due to plant-parasitic nematodes. The northern root-knot nematode, Meloidogyne hapla, is the most important perennial ornamental pathogen in northern North America; it causes over 20% yield loss in Hemerocallis spp. production and reduces marketability and distribution. A field trial was established in 2018 to 2020 at a Michigan commercial nursery to determine effective and long-term management strategies to reduce nematode population levels. Eleven treatments were tested: a control, four bio-nematicides, two nematicides, a nematicide root dip, and three compost blends. Soil samples were taken three times per year, along with annual root samples and plant height measurements. Results indicated that TerraClean 5.0 (hydrogen peroxide) and Majestene 304 ( Chromobacterium subtsugae) nematicides best controlled M. hapla populations by 49 and 37%, respectively, compared with the control, whereas Indemnify (fluopyram) significantly increased plant biomass and yields by 31%. A greenhouse study was conducted to determine the impact of M. hapla on Hemerocallis spp. production by inoculating daylily with varying nematode inoculation densities. Even at low population levels, plant biomass reductions were observed, and M. hapla was readily able to reproduce on Hemerocallis spp. These experiments highlight the importance of managing M. hapla and provide effective, alternative management methods that can reduce the application of fumigants and prevent yield losses to increase profitability for ornamentals.

Transcriptomic analysis of Sitophilus zeamais in response to limonene fumigation.

Frequent application of chemical fumigants has contributed to the development of resistance in stored-product pests. Essential oils provide a novel and environmentally friendly alternative to conventional chemical pesticides. In this work, the fumigant activity of Taxodium 'zhongshansha' essential oil (TZEO) and main active components against Sitophilus zeamais were evaluated. In addition, the molecular mechanisms mediating the fumigant activity of limonene were assessed. TZEO showed strong fumigant activity against Sitophilus zeamais, with a 50% lethal concentration (LC50 ) of 22.90 μL L-1 air in 24 h. The main components of TZEO were identified using gas chromatography-mass spectrometry, the main active ingredient (limonene) showed an LC50 of 9.93 μL L-1 air in 24 h which had a serious dose-time-effect. The LC50 value of the positive control (aluminum phosphide) was 1.91 μL L-1 . In total, 3982 up-regulated and 3067 down-regulated genes were sequenced in limonene-fumigated Sitophilus zeamais, the genes related to metabolic detoxification were significantly enriched. The mortality rate of 7day-old Sitophilus zeamais adult mediated with knockdown of SzCYP6MS5 and SzCYP6MS6 raised up to 65.67% and 67.65% after fumigation with limonene in 24 h, respectively. The results showed that SzCYP6MS5 and SzCYP6MS6 are closely involved to the detoxification of limonene. In this study, candidate genes affected by limonene treatment in Sitophilus zeamais were identified. These findings provided insights into the systemic metabolic response of Sitophilus zeamais to limonene and established a basis for the development of limonene as a botanical pesticide for the control of stored-product pests. © 2022 Society of Chemical Industry.

Activation effect of soil available nitrogen, manganese and cobalt after addition of different fumigants

Soil fumigation is a well-established method for controlling soil-borne diseases. Better quantification of soil available nitrogen and trace elements may provide recommendations on the safe and effective application of soil fumigants. The effects of four fumigants on the available soil nitrogen and trace elements (including Mn, Co, Ni, Cu, Zn and Cd) were investigated in the laboratory incubation with agricultural soil. The results showed that soil fumigation increased soil mineral nitrogen and available Mn, Co, Ni. A significant increase of soil NH4 +-N and available Mn was observed in all fumigation treatments. Chloropicrin treatments showed the largest increase of soil NH4 +-N. In addition, chloropicrin and dazomet increased Mn and Co to a greater extent than dimethyl disulfide and 1,3-dichloropropene in soil. Available Mn content after chloropicrin fumigation has increased by 2.2 times compared with control treatments, and available Co content in dazomet treatments is also 2.8 times more than untreated control. In fumigated soil, the steady increase of soil available elements is beneficial to nutrient uptake by plants. Soil fumigation created an activation effect on soil mineral nitrogen and available trace elements, which may increase their bioavailability to plants and promote plant growth.

Indexing of ground water vulnerability in Guntur district, Andhra Pradesh using GIS based agricultural drastic model

Agricultural activities especially application of fertilizers, pesticides and fumigants have been identified as one of the non-point sources of pollutants which leach various pollutants from agricultural land through the unsaturated zone and groundwater zone gives rise to contamination to groundwater and soil, which poses serious detrimental risk in rural areas. To assess the groundwater vulnerability and analyze the risk, research was carried out in Agricultural areas of Guntur District, Andhra Pradesh. The GIS-based Agricultural vulnerability indexing method (DRASTIC) is selected in this study, which identifies vulnerability zones and is helpful in formulation of strategies to mitigate adverse impact of factors responsible for ground water pollution. Seven DRASTIC layers using parameters such as groundwater influencing parameters were created. Rates and weights were assigned to each parameter layer. By overlapping the layers in ArcGIS, the aquifer vulnerability map was prepared. By multiplying each parameter rate by its weight and adding for all layers Agricultural DRASTIC index number is determined. The results indicated that the Agricultural vulnerability Index in the study area ranged from 72-196 is determined. The developed maps are validated with nitrate concentrations. Different parameters like EC, pH, Ca, Mg, K Na, and NO3 was estimated and correlated to estimate the degree of association. It was observed from the developed Agricultural vulnerability maps for Guntur District that 10.56% of the study area falls under low vulnerable zone, 39.98% under moderate zone and 49.46% under high vulnerable zone due to agricultural leachates in cropped areas.

Evaluation of non-fumigant chemical and biological nematicides for strawberry production in Florida

In Florida, strawberry is an economically important horticultural crop. Plant-parasitic nematodes present a significant obstacle for strawberry growers in the sandy soils found in this state. Historically, nematodes have been controlled through the application of soil fumigants; however, there is interest in exploring the use of non-fumigant nematicides that can provide similar levels of control and at the same time be more environmentally friendly than fumigants. Using two field experiments, the effects of non-fumigant chemical and biological nematicides on plant vigour and fruit yield, populations of plant-parasitic nematodes, and populations of free-living nematode feeding groups were evaluated. In experiment 1, soil fumigation with metam potassium, as well as all non-fumigant chemical nematicides (fluopyram, fluensulfone, fluazaindolizine) failed to increase plant vigour, fruit yield, or suppress populations of plant-parasitic nematodes. In experiment 2, fluopyram increased fruit yield and suppressed Belonolaimus longicaudatus populations by the end of the growing season. Biological nematicides (Dazitol®, Majestene®, and Nemakill®) did not enhance crop establishment or suppress plant-parasitic nematode populations. Soil fumigation with 1,3-dichloropropene + chloropicrin provided consistent enhancement of plant vigour and fruit yield, as well as suppressed populations of B. longicaudatus; however, populations of free-living nematodes were also reduced. Overall, soil application of fluopyram shows potential to be a component of an integrated pest management strategy for the control of B. longicaudatus populations on strawberry in Florida.

Effect of Long-Term Continuous Fumigation on Soil Microbial Communities

High value crop producers in California rely heavily on soil fumigation to control a wide array of soil borne pests including nematodes, pathogens and weeds. Fumigants with broad biocidal activity can affect soil microbial communities that contribute to nutrient cycling and plant nutrient uptake which can impact soil health. It is often thought that soil microbial communities make a relatively rapid recovery following fumigation. However, recently it has been found that repeated application of fumigants over time can have greater and longer lasting impacts on soil microorganisms than single fumigation events. Therefore, the main objective of this study was to determine the effect of long-term repeated application of fumigants on soil microbial communities and compare them with non-fumigated and organic sites. Soil samples were collected from fields in Watsonville, CA. Chronosequence sites were defined by number of years of annual fumigation (yaf) with methyl bromide (15, 26, 33, 39 yaf) at the time of sampling, and representative non-fumigated sites were also included for comparison. Phospholipid fatty acid (PLFA) analysis was used to analyze the samples. The canonical variate analysis showed that microbial communities in sites with a longer history of fumigation (33 and 39 yaf) were similar to one another; however, they differed significantly from 15 yaf site and further analysis concluded that non-fumigated sites were significantly different than fumigated sites. This study showed that the proportion of arbuscular mycorrhizal fungi (AMF) was lower in all fumigated (15, 33 and 39 yaf) sites as compared to their non-fumigated counterparts, which could be a threat to sustainability since AMF plays a major role in soil health and quality.

Interaction between nitrification, denitrification and nitrous oxide production in fumigated soils

Soil fumigation can increase mineral nitrogen due to the mineralization of soil microbial biomass killed during the fumigation, and as a result nitrous oxide (N2O) emission would increase. In addition, a fumigant's impact on soil nitrification and denitrification would also alter the dynamics of N2O production in fumigated soils. Laboratory incubation studies were conducted to quantify the dynamic changes in N2O production following various fumigant treatments, and to determine the interaction between nitrification, denitrification and N2O production in fumigated soils. Results showed a substantial increase in NH4+–N and dissolved amino acids (DAA) during 7 days fumigation at 1WAF (week after fumigation). The application of fumigants caused significant inhibition of nitrification. However the results relating to potential denitrification were quite different. The rates of potential denitrification in chloropicrin (Pic) and dazomet (DZ) treatments at 1WAF were 3.5 and 5.6 times higher than the untreated control. Potential denitrification was greatly stimulated after Pic and DZ fumigation. The N2O production rates in Pic and DZ fumigated soil were significantly higher than the untreated control at 1WAF in the tested soil type. The cumulative N2O emissions in Pic and DZ fumigated soil were also significantly higher than the untreated control, but there were no significant differences among 1,3-dichloropropene (1,3-D), dimethyl disulfide (DMDS) and untreated control. A positive relationship between N2O production and potential denitrification (PDN) was observed (r = 0.951, P < 0.01). Pic and DZ are both nitrogenous compounds. The breakdown products of Pic and DZ would be available for microbial-aided denitrification reactions as nitrogen sources leading to N2O production, indicating that Pic and DZ degradation stimulated denitrification activity responsible for soil N2O production.

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

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. 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. 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.

2-D Simulation of Non-isothermal Fate and Transport of a Drip-applied Fumigant in Plastic-mulched Soil Beds. I. Model Development and Performance Investigation

Pre-plant application of toxic fumigants to soil beds covered by plastic film is commonly used in agriculture to control soil-borne pathogens. Plastic mulch covers tend to physically suppress the emissive loss of gaseous fumigant to the atmosphere. When liquid fumigant metham sodium (MS) is applied in irrigation water to field soil, it is rapidly transformed to the gaseous methyl isothiocyanate (MITC). The gaseous MITC is a potential atmospheric contaminant, and any untransformed MS is a potential contaminant of underlying groundwater due to the high water solubility of MS. A finite element numerical model was developed to investigate two-dimensional MITC fate/transport under non-isothermal soil conditions. Directional solar heating on soil beds, coupled heat and water flow in the soil, and non-isothermal chemical transport were included in the model. Field soil data for MITC distribution, soil water content, meteorological data, and laboratory data were used to verify the model for soil beds covered with plastic mulch. Four possible scenarios were considered: low and high drip-irrigation rates and low and high water contents. The movement of the center of MITC mass in the soil profile was effectively simulated. The lower drip-irrigation rate of MS yielded more extensive coverage of MITC in the plastic-covered soil bed. The lower soil air contents due to higher soil water contents for the higher irrigation rate resulted in high concentrations of soil MITC. NRMSE (normalized root mean square error) calculations further verified that the model predicted fumigant fate/transport well under these non-isothermal field conditions.

오이 시설재배시 고구마뿌리혹선충의 경제적피해한계

고구마 뿌리혹선충(Meloidogyne incognita)의 시설재배 오이에 대한 경제적 피해한계를 조사하기 위하여 비닐하우스 내에 합판으로 만든 박스(<TEX>$30{\times}40{\times}15cm$</TEX>)를 묻고 박스 내 토양 <TEX>$100cm^3$</TEX>당 뿌리혹선충 유충의 밀도를 0, 10, 30, 100, 300, 600마리로 조정된 토양을 넣었다. 각 박스에는 '장수신토좌'에 접붙인 '슈퍼만촌'오이 23일 묘를 8월 1일 1포기씩 심고 11월까지 각 구당 오이 수확량을 조사하였다. 뿌리혹선충의 유충밀도와 수량과의 회귀식은 <TEX>$Y=0.82-0.04{\cdot}Log_{10}$</TEX>(Pi+1)로 방제 비용을 감안한 경제적 피해 허용 수준은 정식전 뿌리혹선충 유충의 밀도가 토양 <TEX>$1,000cm^3$</TEX>당 5마리이면 살선충제 입제 살포가 경제적이고, 유충의 밀도가 토양 <TEX>$1,000cm^3$</TEX>당 25마리 이상이면 훈증제를 처리하는 것도 고려해 볼 수 있다. 오이 시설재배시 뿌리혹선충의 피해를 방지하기 위해서는 최소한 정식 수개월 전에 미리 토양 선충 밀도를 조사해야 할 것이다. To determine the economic threshold level of Meloidogyne incognita on cucumber in greenhouse conditions, cucumber seedlings(Cucumis sativa L. cv. 'Super Manchon') grafted on 'Jangsushintozoa'(Cucurbita maxima x Cu. moschata) were planted in wooden boxes(<TEX>$30{\times}40{\times}15cm,\;L{\times}W{\times}D$</TEX>) under a plastic house in August 01 and harvested from Sep. 01-Oct. 30, 2006. The initial nematode population densities(Pi) in the wooden boxes were adjusted to 0, 10, 30, 100, 300, and 600 second-stage juveniles(J2)/100 <TEX>$cm^3$</TEX> soil. The relationship of total fruit yield to Pi level could be adequately described by a linear regression equation, <TEX>$Y=0.82-0.04{\cdot}Log_{10}$</TEX>(Pi+1). Initial nematode densities(Pi) before planting in excess of 5 J2/1,000 <TEX>$cm^3$</TEX> soil caused in total yields loss that is equivalent to the costs of granular nematicide application; Pi level in excess of 25 J2/1,000 <TEX>$cm^3$</TEX> soil caused in total yields loss that exceed the costs for application of fumigants at current control costs. We propose two different management strategies depending on nematode densities, (i) application of non-fumigant granular nematicides for M. incognita Pi level of 5 J2/1,000 <TEX>$cm^3$</TEX> soil and (ii) fumigant treatment with Pi level over 25 J2/1,000 <TEX>$cm^3$</TEX> soil. Soil samples to determine population density of Meloidogyne spp. for advisory purposes should be taken several months before planting time, which allows a period of time enough for implementing management procedures.

Chitinolytic and Microsclerostatic Activity of Iranian Strains of Streptomyces plicatus and Frankia sp. on Olive Isolate of Verticillium dahliae

Among soil-borne fungi, cosmopolitan phytopathogen, Verticillium dahliae Klebahn is responsible for high yield losses in many plant species. Except for solarization in mediterranean countries and except in the few cases where disease-resistant cultivais are available, control of Verticillium wilt in commercial crops has been highly dependent on the application of preplant soil fumigants. Research to develop alternative control measurements should focus on biological approaches aimed at shifting the composition of soil microbial communities to suppress Verticillium. The merits of role of actinomycetes in biological control of soil-borne fungal-pathogens are known, however actinomycetes micioflora of the Iranian soils has not been very well explored in searching for biofungicide agents. At the present research, in vitro studies of some biological effects of two Iranian strains of actinomycetes, Streptomyces plicatus strain 101 and Frankia sp. strain 103, are presented. Both strains revealed enzymatic activity and inhibited production of microscleiotia in V. dahliae. Treating the crude extract with chloroform, denaturized enzymatic activity of both strains. Thermal inactivation point of active phases of S. plicatus was 70 and 90°C and in Frankia sp. was determined as 60°C. Antifungal active phases of S. plicatus tolerate wide range of pH (5-13) but in Frankia sp. active phase tolerates pH 7-9. These two strains may be useful candidates for involving in integrated control programs of Verticillium vascular wilting.

Occupational exposure to aluminium phosphide and phosphine gas? A suspected case report and review of the literature

The manufacture and application of aluminium phosphide fumigants pose risks of inhalation exposure to phosphine gas. This article presents a case report of suspected inhalation exposure to phosphine gas in a manufacturing facility for aluminium phosphide fumigants, which was associated with acute dyspnoea, hypotension, bradycardia and other signs of intoxication. These symptoms resolved within several hours after removal from exposure. A review of the data on human exposures to phosphide fumigants identifies both pesticide applicators and individuals in the vicinity of application to be at risk of accidental exposure and injury from phosphine inhalation. More recent reports have identified risks of phosphine gas inhalation in association with the clandestine production of methamphetamine. Toxicodynamic effects of phosphine result from the inhibition of cytochrome c oxidase and subsequent generation of reactive oxygen species. There remain unanswered questions relating to the toxicokinetics of phosphine, as well as the assessment of human exposure utilizing biomarkers. As initial signs and symptoms of intoxication from phosphine gas may be nonspecific and transient, there is a need for improved recognition of the potential hazards associated with phosphide fumigants and phosphine gas.

Drip Application of Alternative Fumigants to Methyl Bromide for Strawberry Production

Strawberry (Fragaria ×ananassa Duchesne) is a high-value cash crop that benefits from preplant soil fumigation with methyl bromide (MB) and chloropicrin (CP). Methyl bromide will be banned in the U.S. and other developed countries by 2005 for most uses. Potential alternative chemicals to replace methyl bromide for soil fumigation include CP, 1,3-dichloropropene (1,3-D), and methyl isothiocyanate (MITC) generators such as metam sodium (MS). Commercial formulations of these fumigants applied singly and in combination through drip irrigation systems were evaluated at two sites for three consecutive growing seasons as alternatives to MB:CP fumigation for strawberry production. A mixture of 1,3-D and CP was shank injected as Telone C35 (62% 1,3-D and 35% CP) at 374 kg·ha-1. An emulsifiable concentrate (EC) formulation of 1,3-D and CP was applied as InLine (60% 1,3-D and 32% CP) at 236 and 393 L·ha-1 through drip irrigation systems in three amounts of irrigation water (26, 43, and 61 L·m-2). Chloropicrin (CP EC, 96%) was drip applied singly at 130 or 200 L·ha-1. Metam sodium was applied singly as Vapam HL in three amounts of water and in combination with InLine and CP EC. Strawberry growth, fruit yields, disease pressure, and weed biomass were compared to an untreated control and shank injection with MB:CP mixture (67:33) at 425 kg·ha-1. For soils high in pathogen populations, fruit yield from the untreated plots was 34% to 50% relative to the MB:CP treatment. The greatest (95% to 110%) yields relative to MB:CP were in the high rates of the InLine treatments. Yields from simultaneous drip fumigation with a combination of Vapam HL and InLine or CP EC were less (67% to 79%) than yields from shank fumigation with MB:CP due to 1,3-D and CP hydrolysis reactions with Vapam HL or the generated MITC in the irrigation water that reduced the efficacy of these combinations to control soilborne pathogens. Application of reduced rates of InLine or CP EC followed 6 days later with reduced rates of Vapam HL controlled soil borne pathogens and weeds and produced the greatest fruit yield relative to all treatments. Chemical names used: 1,3-dichloropropene (1,3-D); methyl bromide (MB); trichloronitromethane (chloropicrin, CP); sodium methyldithiocarbamate (metam sodium); methyl isothiocyanate (MITC).

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.

Effect of Application Variables on Emissions and Distribution of Fumigants Applied via Subsurface Drip Irrigation

Soil fumigation is useful for controlling soil-borne pests and diseases in high-cash-value crops. Fumigants are highly volatile, and approaches to reduce atmospheric emissions are required to protect human and environmental health. Application of fumigants through drip irrigation has been proposed as a means to decrease fumigant emissions, improve fumigant distribution in soil, and minimize worker exposure. These experiments were conducted to investigate the effect of the configuration of the drip system on the volatilization and distribution of the fumigants 1,3-dichloropropene (1,3-D), propargyl bromide (PrBr), and methyl isothiocyanate (MITC) in bedded systems. Results indicated that changing the drip emitter spacing and using multiple drip lines in each bed had little effect on the emissions and distribution of any fumigant. Increasing the depth of application from 15 to 30 cm reduced volatilization of MITC by approximately 20 to >90%; emissions were reduced due to a decrease in the flux from the bed top, and deeper injection did not change the amount of fumigant volatilized from the bed side slope and furrow. Increasing the application depth resulted in a slight decrease in the rate of fumigant dissipation in soil, indicating the potential for some improvement in pest-control efficacy with deeper application.

Effect of surface tarp on emissions and distribution of drip-applied fumigants.

Soil fumigants are used to control a wide variety of soil-borne pests in high-cash-value crops. Application of soil fumigants through drip irrigation systems is receiving increasing attention as a method to improve the uniformity of fumigant application. Little information is available on the emissions and soil distribution of fumigants following subsurface drip application, or the effect of plastic tarp on fumigant emissions in these systems. In these experiments, the fumigant compounds 1,3-dichloropropene (1,3-D), Vapam (a methyl isothiocyanate (MITC) precursor), and propargyl bromide (PrBr) were applied to soil beds via drip irrigation at 15 cm depth. Beds were tarped with either standard 1-mil high-density polyethylene (HDPE) or a virtually impermeable film (VIF), leaving the furrows bare. Cumulative emissions of 1,3-D, MITC, and PrBr in these tarped bedded systems was very low, amounting to <10% of the applied mass. These experiments were conducted in the winter months, with average air temperatures of 12-15 degrees C. Cumulative emissions of MITC and 1,3-D from a sandy loam field soil were decreased by > or =80% by tarping the bed with VIF rather than HDPE. A large fraction of the 1,3-D and PrBr flux was from the untarped furrows in VIF-tarped plots, indicating that inhibiting volatilization from the furrow will be important in further reducing emissions in these systems. Monitoring the fumigant distribution in soil indicated that tarping the bed with VIF resulted in a more effective containment of fumigant vapors compared to use of a HDPE tarp.

Transformation of chloropicrin and 1,3-dichloropropene by metam sodium in a combined application of fumigants.

Combined application of fumigants is a potential strategy to replace methyl bromide in the control of soil-borne pests. Unfortunately, abiotic and biotic interactions among fumigants restrict some combined application approaches. In this study, the kinetics and mechanisms of reaction between metam sodium (sodium methyldithiocarbamate) and the halogenated fumigants chloropicrin (trichloronitromethane) and 1,3-dichloropropene (1,3-D) were investigated in aqueous solution. For chloropicrin, an extremely rapid oxidation-reduction process occurred in the presence of metam sodium. The second-order rate constant for the reaction between chloropicrin and metam sodium was approximately 2 orders of magnitude greater than that for the reaction between 1,3-D isomers and metam sodium. Transformation of 1,3-D by metam sodium was associated with an aliphatic S(N)2 nucleophilic substitution process. The nucleophilic reaction of cis-1,3-D with metam sodium was significantly faster than that of the trans isomer and was correlated with a lower reaction activation energy for the cis isomer in the transition state. Combining Telone C-35 (65% 1,3-D and 35% chloropicrin) and metam sodium in solution might yield some nucleophilic sulfur species, which played an important role in the dissipation of 1,3-D. The incompatibility of chloropicrin and 1,3-D with metam sodium was also examined in soil under different application scenarios. Simultaneous application of metam sodium with chloropicrin or 1,3-D accelerated the transformation of the two halogenated fumigants, reducing their availability in soil. A sequential strategy for multiple fumigants was developed, which could be applied without the loss of active ingredient that occurs due to the reaction between fumigants. The proposed methodology may enhance pest control while maintaining environmental protection.