Soil properties, presence of microorganisms, application dose, soil moisture and temperature influence the degradation rate of Allyl isothiocyanate in soil

Encapsulated allyl isothiocyanate improves soil distribution, efficacy against soil-borne pathogens and tomato yield

BACKGROUND

Crop quality, yield and farmer income are reduced by soil-borne diseases, nematodes and weeds, although these can be controlled by allyl isothiocyanate (AITC), a plant-derived soil fumigant. However, its efficacy against soil-borne pathogens varies, mainly because of its chemical instability and uneven distribution in the soil. Formulation modification is an effective way to optimize pesticide application. We encapsulated AITC in modified diatomite granules (GR) and measured the formulation's loading content and stability, environmental fate and efficacy against soil-borne pathogens, and its impact on the growth and yield of tomatoes.

RESULTS

We observed that an AITC loading content in the granules of 27.6% resulted in a degradation half-life of GR that was 1.94 times longer than 20% AITC emulsifiable concentrate in water (EW) and shorter than AITC technical (TC) grade. The stable and more even distribution of GR in soil resulted in relatively consistent and acceptable control of soil-borne pathogens. Soil containing AITC residues that remained 10-24 days after GR fumigation were not phytotoxic to cucumber seeds. GR significantly reduced soil-borne pest populations, and tomato growth and yield increased as AITC dosage increased. GR containing an AITC dose of 20 g m-2 effectively controlled pathogens in soil for about 7 months and improved tomato yield by 108%.

CONCLUSION

Our research demonstrates the benefits of soil fumigation with loaded AITC over other formulations for effective pest control, and improved tomato plant growth and fruit yield. Fumigant encapsulation appears to be a useful method to improve pest and disease control, environmental performance and fumigant commercial sustainability. © 2024 Society of Chemical Industry.

Suppression of Phytophthora capsici in Chile Pepper Using Brassica juncea and Hordeum vulgare Cover Crop Residues and Trichoderma harzianum as a Biocontrol Agent

Phytophthora blight, caused by Phytophthora capsici, is a serious disease of many vegetable crops worldwide. In New Mexico, U.S.A., the disease affects chile pepper (Capsicum annuum L.), a major crop in the state. There is no single tool that effectively controls the disease. Continuous research is needed in identifying combination of tools that can reduce the impact of Phytophthora blight. We explored the potential of combining cover crops and biocontrol agents to reduce soilborne diseases. This study aimed to evaluate the effects of Indian mustard (Brassica juncea L.) cover crop on the antagonistic ability of Trichoderma harzianum against P. capsici in vitro and to quantify the impacts of combining soil amendment with residues from B. juncea and barley (Hordeum vulgare L.) cover crops and plastic covering on infection of chile pepper seedlings by P. capsici under greenhouse conditions. Volatiles from macerated tissue of B. juncea significantly reduced P. capsici and T. harzianum growth in the absence of soil by 89.0 and 79.0%, respectively. When incorporated in soils, volatiles from macerated tissue of B. juncea significantly reduced P. capsici and T. harzianum by 33.4 and 7.8%, respectively. T. harzianum was more resilient to B. juncea biofumigation than P. capsici. Significant reduction in disease incidence was observed with B. juncea-fumigated soil, while no disease suppression was observed with soil incorporation of H. vulgare residues. Covering soil with plastic was necessary for increasing the efficacy of B. juncea biofumigation.

Comparison of drip-irrigated or injected allyl isothiocyanate against key soil-borne pathogens and weeds

BACKGROUND

Allyl isothiocyanate (AITC) is a soil biofumigant used for controlling soil-borne pests that reduce the growth, quality, and yield of food crops. Its effectiveness against pathogens depends largely on its distribution in the soil, which is influenced mainly by the soil water content and application method. The distributions of AITC when injected with different moisture content or drip-irrigated into soils were compared.

RESULTS

AITC injected at 50 g m-2 only diffused 10 cm deep in soil column with 5, 10 or 15% soil moisture content. The gas AITC peak concentration was 0.64 μg cm-3 at 5% moisture content. Diffusion was reduced when moisture content increased to more than 15%. The results of adsorption kinetics and release indicated that AITC's limited distribution was due to its low vapor pressure. AITC applied by drip irrigation at 7.5 g m-2 diffused 15 cm laterally and 30 cm deep where it reached concentrations of 0.022 μg cm-3 and 0.035 μg g-1 , respectively. Some soil-borne pathogens, nematodes and weed seeds closed to the point of AITC release were effectively controlled under drip irrigation, but efficacy decreased with increased distance. AITC applied by drip irrigation at 7.5 g m-2 and covered with PE film for 5 days provided a satisfactory efficacy against soil-borne pathogens and weeds without any phytotoxicity.

CONCLUSION

Our results indicated that AITC applied by drip irrigation was more effective than injection, which will guide applicators on methods to optimize the application of AITC for efficient control of key pests and weeds. © 2023 Society of Chemical Industry.

Effects of soil factors on dimethyl disulfide desorption and the risk of phytotoxicity to newly-planted seedlings

Dimethyl disulfide (DMDS) is a relatively new soil fumigant used in agro-industrial crop production to control soil-borne pests that damage crops and reduce yield. The emissions of DMDS after fumigation reduce soil concentrations thus reducing the risk of phytotoxicity to newly planted crops. However, the factors affecting the desorption of DMDS from soil are unclear. In our study, the desorption characteristics of DMDS from soil were measured in response to continuous ventilation. The degradation of DMDS in soil was examined by thermal incubation. The phytotoxic response of newly-planted cucumber (Cucumis sativus) seedlings to DMDS residues was measured by a sand culture experiment. The results showed DMDS desorption and degradation rates fit a first-order model; that 92% of the DMDS desorption occurred in the first hour after fumigant application; and that residue concentrations in the soil at the end of the ventilation period were unlikely to be phytotoxic to newly-planted cucumber seedlings. By the third day of ventilation, the average desorption rate (ADR) of DMDS in Wenshan soil was 4.0 and 3.6 times, respectively, faster than that in Shunyi and Suihua soils and the ADR of DMDS in soil decreased by 40.0% when the soil moisture content increased from 3% to 12% (wt/wt). Moreover, within one hour of ventilation, the ADR of DMDS in soil decreased by 20.1% when the soil bulk density increased from 1.1 to 1.3 g cm-3. The degradation of DMDS in soil, however, was mostly influenced by soil type and moisture content. A slow degradation rate resulted in a high initial desorption concentration of DMDS in soil. Our results indicated that DMDS desorption from soil in response to continuous ventilation was affected by the soil type, moisture content and bulk density. Rapid degradation of DMDS in soil will lower the risk of phytotoxic residues remaining in the soil and reduce emissions during the waiting period. Acceleration of emissions early in the waiting period by managing soil moisture content or increasing soil porosity may shorten the duration of emissions. Alternatively, soil extraction technology could be developed to recover and reduce fumigant emissions.

Assessment of the Hydrolysis of Pydiflumetofen and Its Degradation Characteristics in Agricultural Soils

Pydiflumetofen is a potent fungicide that effectively inhibits pathogenic fungal growth by regulating succinate dehydrogenase activity. It effectively prevents and treats various fungal diseases, including leaf spot, powdery mildew, grey mold, bakanae, scab, and sheath blight. Pydiflumetofen's hydrolytic and degradation properties were investigated indoors in four distinct soil types (phaeozems, lixisols, ferrosols, and plinthosols) to assess its risks in aquatic and soil environments. The effect of soil physicochemical properties and external environmental conditions on its degradation was also explored. Hydrolysis experiments found that pydiflumetofen's hydrolysis rate decreased with increasing concentration, regardless of the initial concentration. Furthermore, an increasing temperature significantly enhances the hydrolysis rate, with neutral conditions having higher degradation rates than acidic and alkaline conditions. Pydiflumetofen showed a degradation half-life of 10.79-24.82 days and a degradation rate of 0.0276-0.0642 in different soils. Phaeozems soils had the fastest degradation, while ferrosols soils had the slowest. Sterilization significantly reduced its soil degradation rate and extended its half-life, which confirmed that microorganisms were the primary cause. Therefore, when using pydiflumetofen in agricultural production activities, the characteristics of water bodies, soil, and environmental factors must be considered, while minimizing the emissions and environmental impact.

Effects of fertilizers and soil amendments on the degradation rate of allyl isothiocyanate in two typical soils of China

BACKGROUND

Allyl isothiocyanate (AITC) is a soil fumigant that protects plants against soil-borne pathogens, weeds and insects when present in the root-zone. However, the degradation of AITC under different fertilizers and soil amendments affects its emission and pest control efficacy. Degradation rates of AITC in soil amended with organic and inorganic fertilizers, zeolite and biochar were determined in the laboratory to improve its field applications.

RESULTS

The degradation half-lives of AITC were 24.4 and 35.4 h in Fangshan and Yongzhou soils, respectively, without any added fertilizer or soil amendment. Nitrogen fertilizer and organic fertilizer accelerated the degradation rate of AITC, while phosphorus fertilizer had the opposite effect. The degradation rate of AITC on adding unsterilized chicken manure was over 3.5 and 1.1 times higher than that of sterilization in Fangshan and Yongzhou soil. Inorganic and organic fertilizers affected the degradation of AITC by affecting soil microbial activity on the basis of CO₂ cumulative release. The degradation rate of AITC increased more than 0.4 times in response to zeolite, but this was independent of particle size. The AITC degradation rate increased 1.0-2.6 and 0.3-9.7 times in response to biochar made from corn stalk and pine wood, respectively. Cow manure biochar manufactured at different pyrolyzation temperatures had different effects on the degradation rate of AITC.

CONCLUSION

Soil type, fertilizers and soil amendments differentially affect the degradation rate of AITC by changing soil physicochemical characteristics, microorganisms, etc., which shows great potential in reducing AITC emissions and increasing pest control efficacy when AITC is applied commercially. © 2022 Society of Chemical Industry.

Superabsorbent hydrogel as a formulation to promote mineralization and accelerate degradation of acetochlor in soils

The excessive use of herbicides had caused serious environmental pollution and ecological problems. Therefore, it is imperative to explore an effective method to reduce herbicide residues and pollution. In the present study, we used superabsorbent hydrogels coated ¹⁴C-acetochlor (SH-ACE) to investigate its behavior in different soils under oxic conditions. After 100 days, the mineralization by SH-ACE was increased by 2.3%, 2.5% and 3.3% in the red clay soils, fluvio-marine yellow loamy soils and coastal saline soils, respectively, compared to the control group. This result indicated that the SH-ACE treatment resulted in more complete degradation and detoxification of acetochlor. In addition, the dissipation rates of acetochlor were significantly faster in the SH-ACE treatment, which reduced the persistence of acetochlor. The probable degradation pathways of acetochlor involved dechlorination, hydroxylation, deethoxymethylation, and the formation of thioacetic acid derivatives in the two treatments, but the contents of transformation products were completely different. These findings suggest that the SH-ACE treatment has a significant effect to accelerate the degradation of acetochlor. When developing green pesticides, we emphasize that superabsorbent hydrogel coating treatment should be considered as a promising method for ecological safety in the environment.

Fate of the neonicotinoid insecticide cycloxaprid in different soils under oxic conditions

Neonicotinoids are the most widely used pesticides worldwide due to their high toxicity to invertebrates. However, these compounds also increase the probability of environmental contamination. Cycloxaprid (CYC) is a promising neonicotinoid due to its insecticidal effectiveness and low cross resistance, but little is known about its fate in soils. Using radioisotope tracing techniques, the fate of ¹⁴C-labeled CYC enantiomers and racemic mixtures in aerobic soil was investigated in this research. After 100 d of incubation, the extractable residue (ER) of CYC decreased from 89.6% to 36.4% in red clay soil, from 46.1% to 10.1% in yellow loam soil, and from 93.2% to 12.2% in coastal saline soil. The radioactivity was substantially lower in methanol than in the other two solvents, but the distribution of CYC ER in various solvents across the three soils dramatically differed. The fraction of radioactive CYC that diffused into bound residue (BR) in the three soils increased over time to 56.8-83.0%. The variability in BR was influenced by soil properties such as organic matter concentration, pH, and residual microbial activity. Among the soils, yellow loam soil had the greatest tendency (53.0-83.0%) to form BR, while red clay soil showed the lowest capacity (7.5-61.2%). Cumulative mineralization (MI) to ¹⁴CO₂ accounted for 0.12-0.23%, 6.69-7.31% and 14.82-20.06% in acidic soil, neutral soil and alkaline soil, respectively, which suggests that the environmental fate of chiral pesticides may be influenced by soil pH. No stereoselective behavior was detected in this study. These findings provide a framework to assess the environmental impact and ecological safety of CYC application.

Combination of modified biochar and polyurea microcapsules to co-encapsulate a fumigant via interface polymerization for controlled release and enhanced bioactivity

BACKGROUND

Soil fumigants-the most effective agrochemicals for managing soil-borne diseases-have been used extensively. However, high volatility, moderate toxicity and insufficient effective duration considerably limit their application. In the present study, interface polymerization was used to combine modified biochar (BC) and polyurea microcapsules (MCs) to co-encapsulate allyl isothiocyanate (AITC), developing a model fumigant for controlled release (AITC@BC-MCs).

RESULTS

The physical characteristics of BC modified by sand-milling were significantly improved. In addition, chemical properties and morphological features of AITC@BC-MCs characterized by integrated methods revealed successful preparation of BC-MCs. Compared with monolayer MCs, BC-MCs could significantly delay AITC release owing to the composite obstruction effect. Moreover, modifying BC endowed the cargo molecules with a pH-responsive release property. Additionally, this composite showed a longer persistent duration by prolonging AITC degradation half-life, which was 3.2-3.5-fold greater than that of the AITC technical concentrate under different soil conditions. Finally, the control efficacy of the AITC@BC-MC against pathogens, including nematodes and fungi, as well as against weeds was significantly enhanced at the same dose, but the composite did not inhibit seed germination and growth after 10 days when fumigated soil was aerated.

CONCLUSION

Construction of a composite encapsulation system enhanced pesticide efficacy, reduced dose via controlled release and delayed fumigant degradation in soil, indicating the great potential of this strategy for developing an effective and environmentally friendly fumigant formulation. © 2021 Society of Chemical Industry.

Allyl Isothiocyanate in the Volatiles of Brassica juncea Inhibits the Growth of Root Rot Pathogens of Panax notoginseng by Inducing the Accumulation of ROS

The cultivation of Panax notoginseng is often seriously hindered by root rot disease caused by the accumulation of soil-borne pathogens. Here, the inhibitory activity of Brassica juncea volatiles on P. notoginseng root rot pathogens was assessed and compounds in volatiles were identified. Furthermore, the antimicrobial activity and mechanism of allyl isothiocyanate (AITC) were deciphered by integrated transcriptome and metabolome analyses. The volatiles of B. juncea showed dose-dependent antimicrobial activity against root rot pathogens. AITC, identified as the main volatile compound, not only significantly inhibited pathogen growth in vitro but also suppressed root rot disease in the field. Integrated transcriptomic and metabolomics analysis revealed that AITC inhibited Fusarium solani by interfering with energy production and induced the accumulation of ROS by decreasing the content of glutathione (GSH). In summary, B. juncea releases AITC to inhibit soil-borne pathogens and could be used as a rotation crop or soil fumigant to alleviate root rot disease.

Effect of bioactive compounds released from Brassicaceae defatted seed meals on bacterial load in pig manure

Animal manure application to soils is considered to be one of the main cause of antibiotic and bacterial pathogen spread in the environment. Pig livestock, which is the source of one of the most used fertilizer for cultivated land, is also a hotspot for antibiotics and antibiotic-resistant bacteria. Besides harsh chemical and physical sanitization treatments for the abatement of antibiotics and bacterial load in livestock waste, more sustainable and environmentally friendly strategies need to be considered. In this context, the use of natural substances which are proved useful for pest and disease control is currently under exploration for their role in the reduction of bacterial pathogen population. Among these, plants and derived products from the Brassicaceae family, characterized by the presence of a defensive glucosinolate-myrosinase enzymatic system, have been successfully exploited for years in agriculture using the so-called biofumigation technique against crop diseases. Although the application of biofumigation to suppress a range of soil borne pests has been well documented, no studies have been examined to reduce bacterial population in animal waste. In the present study, the release and the antibacterial activity of bioactive compounds deriving from different Brassicaceae defatted seed meals against pathogens and bacterial population in pig manure is addressed. Rapistrum rugosum and Brassica nigra defatted seed meals were found to be the most active products against tested pathogens and able to significantly reduce the bacterial load in the manure.

Effects of soil type, moisture content and organic amendment rate on dimethyl disulfide distribution and persistency in soil

Understanding the distribution and persistence of the fumigant dimethyl disulfide (DMDS) under different soil conditions would contribute to a more environmentally sustainable use of this gas. We determined the effects of soil type, soil moisture content and soil organic amendment rate on DMDS distribution and persistency using soil columns in the laboratory. The peak concentrations of DMDS at 60 cm soil depth in sandy loam soil, black soil and red loam soil were 1.9 μg cm^-3, 0.77 μg cm^-3, 0.22 μg cm^-3, respectively. The total soil residues of DMDS in sandy loam soil, black soil and red loam soil were 0.4, 1.3 and 1.3%, respectively. The peak concentrations of DMDS at 60 cm soil depth and the total soil residues of DMDS applied decreased from 3.2 μg cm^-3 to 0.9 μg cm^-3 and 3.3 to 0.5% when soil moisture content increased from 6 to 18%, respectively. Incremental increases (0-5%) in organic amendment rates decreased DMDS distribution through the soils and increased soil residues. Wait periods were required of 7, 21 and 21 days after polyethylene (PE) film was removed to reduce residues sufficiently for cucumber seed germination in sandy loam soil, black soil and red loam soil with 12% moisture content and 0% organic amendment rate, respectively. However, no wait period was required for successful cucumber seed germination in sandy loam soils (Beijing) with 6, 12 or 18% moisture content or organic amendment rates of 1 or 5%, respectively, but in commercial practice 7 days delay would be prudent. Our results indicated that soil type, soil moisture content and organic amendment rates significantly affected DMDS distribution, persistency and residues in soil. Those factors should be taken into consideration by farmers when determining the appropriate dose of DMDS that will control soil pests and diseases in commercially-produced crops.

Influence of Allyl Isothiocyanate on the Soil Microbial Community Structure and Composition during Pepper Cultivation

Allyl isothiocyanate (AITC), as a fumigant, plays an important role in soil control of nematodes, soilborne pathogens, and weeds, but its effects on soil microorganisms are unclear. In this study, the effects of AITC on microbial diversity and community composition of Capsicum annuum L. soil were investigated through Illumina high-throughput sequencing. The results showed that microbial diversity and community structure were significantly influenced by AITC. AITC reduced the diversity of soil bacteria, stimulated the diversity of the soil fungal community, and significantly changed the structure of fungal community. AITC decreased the relative abundance of dominant bacteria Planctomycetes, Acinetobacter, Pseudodeganella, and RB41, but increased that of Lysobacter, Sphingomonas, Pseudomonas, Luteimonas, Pseudoxanthomonas, and Bacillus at the genera level, while for fungi, Trichoderma, Neurospora, and Lasiodiplodia decreased significantly and Aspergillus, Cladosporium, Fusarium, Penicillium, and Saccharomyces were higher than the control. The correlation analysis suggested cellulase had a significant correlation with fungal operational taxonomic units and there was a significant correlation between cellulase and fungal diversity, while catalase, cellulose, sucrase, and urease were the major contributors in the shift of the community structure. Our results will provide useful information for the use of AITC in the assessment of environmental and ecological security.

Pesticide treatment in biobed systems at microcosms level under critical moisture and temperature range using an Orthic Solonchaks soil from southeastern Mexico amended with corn husk as support

Agriculture effluents from cleaning and handling equipment used in pesticide applications can contaminate superficial and groundwater sources when not correctly disposed of. Biobeds using soil enriched with amendments represent a viable technology to control and minimize pesticide pollution of soil and water in farmlands. They are usually installed outdoors without protection, making them vulnerable to rain flooding, lack of moisture, drought, and intense heat or cold. Temperature (T) and moisture (M) of the biomixture are considered two of the most important physical factor affecting pesticide dissipation. This study aimed to evaluate the effect of T and M on the dissipation of five of the most used pesticides (carbofuran, atrazine, 2,4-D, diazinon, and glyphosate) in Yucatan State, Mexico. Three experiments using miniaturized biobeds considering optimal temperature and moisture (T of 30 ± 2 °C and 90% water holding capacity [WHC]) were performed. The optimal dissipation time and the effect of T, M variations, and volatilization was determined. The optimal dissipation time was over 14 days. Carbofuran was the least dissipated pesticide and glyphosate the most. The primary factor affecting pesticide dissipation was T (P < 0.05), reaching rates of dissipation of 99% at 45 °C. Variations of M in the biomixture were not significant on pesticide dissipation (P > 0.05). The white-rot fungi were observed; its presence was related to increments of T. Head Space analysis (at 45 °C) showed low pesticide volatilization (≤0.03%) for all pesticide used were quantified; water vapor condensation could reduce the pesticide volatilization for experimental conditions.

Temperature and Aging Affect Glyphosate Toxicity and Fatty Acid Composition in Allonychiurus kimi (Lee) (Collembola)

Glyphosate is the most used herbicide worldwide, but enormous use of glyphosate has raised concerned about its environmental loadings. Although glyphosate is considered non-toxic, toxicity data for soil non-target organisms according to temperature and aging are scarce. This study examined the toxicity of glyphosate with the temperature (20 °C and 25 °C) and aging times (0 day and 7 days) in soil using a collembolan species, Allonychiurus kimi (Lee). The degradation of glyphosate was investigated. Fatty acid composition of A. kimi was also investigated. The half-life of glyphosate was 2.38 days at 20 °C and 1.69 days at 25 °C. At 20 °C with 0 day of aging, the EC50 was estimated to be 93.5 mg kg-1. However, as the temperature and aging time increased, the glyphosate degradation increased, so no significant toxicity was observed on juvenile production. The proportions of the arachidonic acid and stearic acid decreased and increased with the glyphosate treatment, respectively, even at 37.1 mg kg-1, at which no significant effects on juvenile production were observed. Our results showed that the changes in the glyphosate toxicity with temperature and aging time were mostly dependent on the soil residual concentration. Furthermore, the changes in the fatty acid compositions suggest that glyphosate could have a chronic effect on soil organisms.