Preplant Soil Fumigation Research Articles

A Semi-Selective Medium to Evaluate Over-Summering Survival of Neopestalotiopsis sp. in Florida Strawberry Fields.

Devastating disease outbreaks with leaf spot symptoms and fruit rot caused by a fungus identified as a cryptic species of Neopestalotiopsis have generated concern in the Florida strawberry industry. Some Neopestalotiopsis species are saprobes in soil and plant debris, but the ability of the new Neopestalotiopsis sp. to survive in strawberry debris was unknown. Therefore, the objectives of this study were to develop a semiselective medium for isolation of Neopestalotiopsis spp. and to evaluate Neopestalotiopsis sp. survival in soil and strawberry plant debris over the summer in Florida. The Neopestalotiopsis semiselective medium (NSM) inhibited growth of most fungal species pathogenic to strawberry in Florida, except Neopestalotiopsis rosae, Neopestalotiopsis sp., and Phomopsis obscurans, in addition to Penicillium spp., which are nonpathogenic. However, Neopestalotiopsis species, P. obscurans, and Penicillium spp. could be distinguished in the medium through morphological characteristics. Soil samples arbitrarily collected from six commercial fields toward the end of the season (May) and before (July) and after (September) preplant soil fumigation in the following season were processed with NSM, and Neopestalotiopsis spp. populations were calculated as CFU per gram of soil. CFU ranged from 48.3 to 2,410.8 at the end of the season and from 1.7 to 630.8 before soil fumigation, but Neopestalotiopsis spp. were not recovered after soil treatment. However, 1.7 to 25 CFU were obtained from the nontreated areas in the row middles. Neopestalotiopsis sp. survival was also evaluated on diseased strawberry plants (leaves and crowns) exposed to the environment for 17 months. On leaves, Neopestalotiopsis spp. were recovered for 6 months before leaf decomposition, whereas the number of CFU on crowns declined monthly, but colonies were still recovered during the final evaluation months. A high-resolution melting analysis confirmed most of the colonies from soil and crowns were the new Neopestalotiopsis sp. Our results show Neopestalotiopsis sp. can survive in soil and strawberry debris under Florida summer conditions and may serve as a source of inoculum for the subsequent season.

Phosphorus Fertilization Can Improve Young Almond Tree Growth in Multiple Replant Settings

Young almond (Prunus amygdalus) orchards replanted where old orchards of stone fruits (Prunus sp.) have been removed are subject to physical, chemical, and biotic stressors. Among biotic challenges, for example, is almond/stone fruit replant disease (ARD; formally known as Prunus replant disease), which specifically suppresses the growth and yields of successive almond and other stone fruit plantings and is caused, in part, by a soil microbial complex. During four orchard trials representing different almond replant practices and scenarios in the San Joaquin Valley in California, we examined the impacts of phosphorus (P) fertilization on the growth of replanted almond. During all trials, P was applied to tree root zones just after replanting, and the impact was assessed according to trunk cross-sectional area (TCSA) growth for 2 years. Expt. 1 was performed where a previous almond orchard was cleared using whole orchard recycling (i.e., the old orchard was “chipped” and then turned into the soil). The land was replanted without preplant soil fumigation. We tested separate fertilizer treatments based on various P, nitrogen, micronutrient, and “complete” formulations. Expt. 2 was also performed where an old almond orchard was recycled, but the soil was preplant-fumigated before replanting. Here, we tested only P fertilization. Expts. 3 and 4 were conducted where an old peach (Prunus persica) orchard was removed. Here, P and nitrogen fertilizer treatments were tested among additional factors, including preplant soil fumigation (Expts. 3, 4) and whole orchard recycling chips (Expt. 4). During all four trials, P fertilization (P at 2.2 to 2.6 oz/tree within a few weeks after planting) significantly increased TCSA growth. The growth benefit was nuanced, however, by almond cultivar, date of replanting, rootstock, and other site-specific factors. Although P fertilization did not match the benefit of preplant soil fumigation for the management of ARD, our data indicated that P fertilization can improve the growth of young almond orchards in diverse replant settings with or without preplant soil fumigation and should be considered by California almond producers as a general best management practice.

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.

Spatial and Temporal Changes of Soil Microbial Communities in Field Tomato Production as Affected by Anaerobic Soil Disinfestation

Anaerobic soil disinfestation (ASD) has been demonstrated as an effective alternative to pre-plant chemical soil fumigation (CSF) commonly used to control soilborne pathogens. However, the ASD effects on spatial and temporal changes in soil microbial communities remain poorly understood in production systems with low soilborne disease pressure. The objective of this study was to assess the influence of ASD treatments on soil microbial community composition at different soil depths during the spring tomato production season in Florida. Soil treatments included ASD using 6.9 m3 ha−1 of molasses with 11 Mg ha−1 of composted poultry litter (CPL) (ASD0.5), ASD with 13.9 m3 ha−1 of molasses and 22 Mg ha−1 CPL (ASD1.0), and chemical soil fumigation (CSF) using a mixture of 1,3-dichloropropene and chloropicrin. Soil microbial community composition was measured at soil depths of 0–15 and 15–30 cm using phospholipid fatty acid (PLFA) analysis at 0, 36, 76, and 99 days after transplanting (DAT). Fatty acid methyl esters were categorized into biomarker groups including total microbial biomass (TMB), G+ bacteria (G+), G− bacteria (G−), actinomycetes (Actino), arbuscular mycorrhizal fungi (AMF), protozoa, and general fungi (F). Soil concentrations of G+, Actino, F, AMF, and the ratio of F:bacteria (B) were significantly impacted by a soil treatment × soil depth × sampling time three-way interaction. All the microbial biomarkers were significantly affected by soil treatment × sampling depth two-way interactions except for protozoa and F:B ratio. Concentrations of TMB, Actino, AMF, F, G+, and G− bacteria were significantly increased in ASD treated soils at both 0–15 and 15–30 cm soil depths across different sampling times compared with CSF. In addition, the concentrations of G+ and G− bacteria, AMF, F, and TMB were higher at 0–15 vs. 15–30 cm soil depth under ASD treatments, whereas no soil depth differences were observed in CSF. Discriminant analysis further confirmed that soil microbial community composition was distinctly different in CSF compared with ASD treatments. The soil microbial profile was well-differentiated between the two soil depths under ASD treatments but not in CSF, while the enhancement of PLFA biomarkers by ASD decreased with increasing soil depth.

Top-down and bottom-up estimates of anthropogenic methyl bromide emissions from eastern China

Abstract. Methyl bromide (CH3Br) is a potent ozone-depleting substance (ODS) that has both natural and anthropogenic sources. CH3Br has been used mainly for preplant soil fumigation, post-harvest grain and timber fumigation, and structural fumigation. Most non-quarantine and pre-shipment (non-QPS) uses were phased out by 2005 for non-Article 5 (developed) countries and by 2015 for Article 5 (developing) countries under the Montreal Protocol on Substances that Deplete the Ozone Layer; some uses have continued under critical-use exemptions (CUEs). Under the protocol, individual nations are required to report annual data on CH3Br production and consumption for quarantine–pre-shipment (QPS) uses, non-QPS uses, and CUEs to the United Nations Environment Programme (UNEP). In this study, we analyzed high-precision, in situ measurements of atmospheric mole fractions of CH3Br obtained at the Gosan station on Jeju Island, South Korea, from 2008 to 2019. The background mole fractions of CH3Br in the atmosphere at Gosan declined from 8.5±0.8 ppt (parts per trillion) in 2008 to 7.4±0.6 ppt in 2019 at a rate of -0.13±0.02 ppt yr−1. At Gosan, we also observed periods of persistent mole fractions (pollution events) elevated above the decreasing background in continental air masses from China. Statistical back-trajectory analyses showed that these pollution events are predominantly traced back to CH3Br emissions from eastern China. Using an interspecies correlation (ISC) method with the reference trace species CFC-11 (CCl3F), we estimate anthropogenic CH3Br emissions from eastern China at an average of 4.1±1.3 Gg yr−1 in 2008–2019, approximately 2.9±1.3 Gg yr−1 higher than the bottom-up emission estimates reported to UNEP. Possible non-fumigation CH3Br sources – rapeseed production and biomass burning – were assessed, and it was found that the discrepancy is most likely due to unreported or incorrectly reported QPS and non-QPS fumigation uses. These unreported anthropogenic emissions of CH3Br are confined to eastern China and account for 30 %–40 % of anthropogenic global CH3Br emissions. They are likely due to delays in the introduction of CH3Br alternatives, such as sulfuryl fluoride (SO2F2), heat, and irradiation, and a possible lack of industry awareness of the need for regulation of CH3Br production and use.

Management of Chrysanthemum Verticillium Wilt through VIF Soil Mulching Combined with Fumigation at Label and Reduced Rates

Pre-plant soil fumigation for managing soilborne pathogens is practiced worldwide in several intensive ornamental and vegetable production areas. However, global regulations are currently implemented to minimize use of these chemicals. According to these policies, the efficacies of dazomet (DZ, Basamid Granulat®) applied alone to soil and under virtually impermeable film (VIF) at reduced (247.5 kg ha−1 a.i.) and label (495 kg ha−1 a.i.) rates were assessed in managing natural infections of Verticillium wilt and in reducing yield losses on greenhouse chrysanthemum plantations in two trials carried out in the 2012 and 2013 seasons. The performances of this fumigant at a lower rate combined with VIF application were also compared with standardized metam-sodium (MS, Divapan®) fumigation applied at 510 L ha−1 a.i. under VIF and application of dazomet at label rate alone to bare soil. Temperatures were monitored at 20-cm depth in plots covered (VIF) throughout the entire fumigation period. Although all fumigation treatments significantly reduced the infection level by V. dahliae on chrysanthemum, the performances differed among them. DZ and MS applied at label rates under VIF showed the most effectiveness in controlling Verticillium wilt of chrysanthemum. However, DZ applied to soil at a low rate under VIF mulching showed good performances, which were always better than application of DZ alone at label rate to bare soil. Moreover, when combining a reduced rate of DZ with VIF mulching, chrysanthemum yield losses were reduced in a similar manner to the label rate application under VIF. Based on these findings, DZ application at a reduced rate could be suggested on a large scale to prevent Verticillium attacks on chrysanthemum cultivated on a protected crop. Future studies should be performed to verify the ability of VIF application in inducing high temperatures in soil and above all in enhancing performances of soil fumigation at low rates performed with other natural and chemical sterilants.

Characterization of soils conducive and non-conducive to Prunus replant disease.

Successive orchard plantings of almond and other Prunus species exhibit reduced growth and yield in many California soils. This phenomenon, known as Prunus replant disease (PRD), can be prevented by preplant soil fumigation or anaerobic soil disinfestation, but its etiology is poorly understood and its incidence and severity are hard to predict. We report here on relationships among physicochemical variables, microbial community structure, and PRD induction in 25 diverse replant soils from California. In a greenhouse bioassay, soil was considered to be “PRD-inducing” when growth of peach seedlings in it was significantly increased by preplant fumigation and pasteurization, compared to an untreated control. PRD was induced in 18 of the 25 soils, and PRD severity correlated positively with soil exchangeable-K, pH, %clay, total %N, and electrical conductivity. The structure of bacterial, fungal, and oomycete communities differed significantly between the PRD-inducing and non-inducing soils, based on PERMANOVA of Bray Curtis dissimilarities. Bacterial class MB-A2-108 of phylum Actinobacteria had high relative abundances among PRD-inducing soils, while Bacteroidia were relatively abundant among non-inducing soils. Among fungi, many ASVs classified only to kingdom level were relatively abundant among PRD-inducing soils whereas ASVs of Trichoderma were relatively abundant among non-inducing soils. Random forest classification effectively discriminated between PRD-inducing and non-inducing soils, revealing many bacterial ASVs with high explanatory values. Random forest regression effectively accounted for PRD severity, with soil exchangeable-K and pH having high predictive value. Our work revealed several biotic and abiotic variables worthy of further examination in PRD etiology.

Efficacy and economics evaluation of seed rhizome treatment combined with preplant soil fumigation on ginger soilborne disease, plant growth, and yield promotion.

Ginger (Zingiber officinale Roscoe) is widely planted around the world. Owing to continuous planting, ginger is seriously affected by soilborne fungi, bacteria, and nematodes. Although preplant soil fumigation is an effective prevention strategy of soilborne diseases, individual fumigant and technology could not provide effective control of ginger soilborne disease. In our research, different combinations of soil fumigants and seed rhizome treatments were evaluated by monitoring the soil pathogens population, ginger growth, yield, and estimation of economic benefits. Soil fumigation effectively reduced the population of soilborne pathogens, and chloropicrin had a better control effect on soilborne pathogens than dazomet did. Preplant soil fumigation and seed rhizome treatment not only provide good control of soilborne disease, but also reduced the incidence of plant foliar pest and disease. Average yield increase rate of seed rhizome treatment was 12.0%; the highest yield increase was 24.4%. The average cost of seed rhizome treatment only increased by about 2.86%, but the rate of net revenue increase for the seed rhizome treatment reached up to 19.1%. Seed rhizome treatment is a very cost-effective soilborne disease control technology. In the management of soilborne diseases, the combined application of soil fumigation and seed rhizome treatment can reduce the risk of crops infected by soilborne diseases and ensure high and stable crop yields. © 2021 Society of Chemical Industry.

Tomato tolerance and purple nutsedge control with sulfuryl fluoride mixes

AbstractSulfuryl fluoride (SF) is currently used as a fumigant for control of drywood termites and insects in building structures, vehicles, wood products, postharvest commodities, and food processing facilities. This research investigated the feasibility of using SF as a preplant soil fumigant for purple nutsedge control in plastic-mulched tomato production. SF treatments included SF injected through drip tapes or SF injected through drip tapes a few hours following shank injection of chloropicrin (Pic). Results revealed that SF alone at 224, 336, or 448 kg ha−1 was generally less effective compared with when it was applied in conjunction with Pic at 168 kg ha−1. SF alone provided inconsistent control of purple nutsedge. In contrast, SF + Pic was as efficacious or more efficacious on purple nutsedge than the industry standards, including 1,3-dichloropropene (1,3-D) plus Pic and metam potassium. None of the fumigant treatments visually injured tomato plants, stunted growth, or adversely affected tomato yield. In one of the four tomato seasons, tomato plants growing in plots fumigated with SF + Pic resulted in taller tomato plants and higher markable yields. Results indicate that soil fumigation with SF + Pic is safe on plastic-mulched tomato and effectively controls purple nutsedge.

Analysis of the Soil Fumigant, Dimethyl Disulfide, in Swine Blood by Dynamic Headspace Gas Chromatography–Mass Spectroscopy

Plant parasites and soilborne pathogens directly reduce the overall yield of crops, vegetables, and fruits, negatively impacting the market demand for these products and their net profitability. While preplant soil fumigation helps maintain the consistent production quality of high-value cash crops, most soil fumigants are toxic to off-target species, including humans. Dimethyl disulfide (DMDS) has recently been introduced as a relatively low toxicity soil fumigant. Although DMDS exhibits low toxicity compared to other soil fumigants, it is volatile and exposure can cause eye, nasal, and upper respiratory tract irritation, skin irritation, nausea, dizziness, headache, and fatigue. While there is one analysis method available for DMDS from biological matrices, it has significant disadvantages. Hence, in this study, a dynamic headspace gas chromatography–mass spectroscopy (DHS-GC-MS) method was developed for the analysis of DMDS in swine whole blood. This method is highly sensitive and requires only three steps: 1) acid denaturation, 2) addition of internal standard, and 3) DHS-GC-MS analysis. The method produced a wide linear range from 0.1 – 200 µM with an excellent limit of detection of 30 nM. Intra- and interassay accuracy (100±14% and 100±11%, respectively) and precision (<5% and <6% relative standard deviation, respectively) were also excellent. The method worked well to quantify the DMDS levels in the blood of dimethyl trisulfide (DMTS)-treated swine (i.e., DMDS is a byproduct of DMTS treatment) with no interfering substances at or around the retention time of DMDS (i.e., 2.7 min). This simple, rapid, and extremely sensitive method can be used for the quantification of DMDS levels in blood to verify exposure to DMDS or to monitor levels of DMDS following DMTS treatment (e.g., for cyanide poisoning).

Evaluation of integrated management of bacterial wilt of tomato using grafting, biofumigant and plant resistance activator under field conditions

Bacterial wilt, caused by Ralstonia solanacearum, is a major and constant constraint in the production of tomatoes worldwide. A two-season field experiments, laid out in two separate orchards in a randomized complete block design and a split-split plot arrangement with three replications, was conducted to evaluate the integrated effect of grafting, thymol and acibenzolar-S-methyl (ASM) in the management of tomato bacterial wilt disease in a naturally infested soil. Beske and UC82-B tomato cultivars, susceptible to the pathogen, were grafted on a resistant tomato rootstock (Tomachiva) while thymol (0.7% w/v) was applied as a pre-plant soil fumigant. Grafted and non-grafted tomato received ASM as foliar spray after transplanting. Sole or combined application of the enhancers (thymol and ASM) had significant reduction of bacterial wilt incidence in both seasons, from the second to eight weeks after transplanting. At eighth week after transplanting, the effect of combined application of thymol and ASM translated to 100% and 90.3% disease reduction in early and late planting seasons, respectively. Grafted tomato, thymol and ASM combination produced an average yield of 74.3 and 86.9 ton/ha in early and 65.3 and 58.1 ton/ha in late planting seasons respectively. The findings indicated that integrated use of grafting, thymol (0.7% w/v) and ASM (30 µg/ml) could be of great benefit in the control of bacterial wilt of tomato.

Strawberries at the Crossroads: Management of Soilborne Diseases in California Without Methyl Bromide.

Strawberry production has historically been affected by soilborne diseases such as Verticillium wilt. This disease was a major limiting factor in strawberry production in California in the 1950s and was the main reason that preplant soil fumigation with methyl bromide (MB) was developed in the late 1950s. MB fumigation was so successful that over 90% of the commercial strawberry fruit production in California utilized this technique. However, MB was subsequently linked to ozone depletion, and its use was phased out in 2005. The California strawberry industry was awarded exemption to the full phase-out until 2016, when all MB use in strawberry fruit production was prohibited. MB use continues in strawberry nurseries under an exemption to prevent spread of nematodes and diseases on planting stock. This review examines the impact of the MB phase-out on the California strawberry industry and evaluates the outlook for the industry in the absence of one of the most effective tools for managing soilborne diseases. New soilborne diseases have emerged, and historically important soilborne diseases have reemerged. Registration of new fumigants has been difficult and replacement of MB with a new and effective alternative is unlikely in the foreseeable future. Thus, crop losses due to soilborne diseases are likely to increase. Host plant resistance to soilborne diseases has become a top priority for strawberry breeding programs, and cultivars are increasingly selected for their resistance to soilborne diseases. The intelligent integration of a variety of management tactics is necessary to sustain strawberry production in California.

Multitactic Preplant Soil Fumigation with Allyl Isothiocyanate in Cut Flowers and Strawberry

Allyl isothiocyanate (AITC) is a glucosinolate produced in cruciferous plant species. AITC is known to act as a pesticide on microorganisms, insects, and weeds. Synthetic AITC is registered as a biopesticide for agricultural soil treatment use in the United States and elsewhere in the world. Although a potent pesticide, reports on the weed and pathogen control efficacy of synthetic AITC applied as soil disinfectant are highly variable. Due to the low vapor pressure of AITC, questions remain as to whether pest and weed control efficacy can be improved by combining it with other chemicals. The objective of this study was to assess the control efficacy of AITC stand-alone applications vs. applications, in which AITC was combined with the standard-fumigants chloropicrin, 1,3-dichloropicrin, and methyl isothiocyanate. Two shank-applied on-farm field trials were conducted in cut flower [delphinium (Delphinium elatum), ranunculus (Ranunculus asiaticus)] fields, and two drip tape applied field trials in strawberry (Fragaria ×ananassa) fields in California. Weed pressure, weed seed viability, nematode survival, and pathogen survival of Pythium ultimum, fusarium wilt (Fusarium oxysporum), and verticillium wilt (Verticillium dahliae) were assessed. Cumulative yearly yield of marketable fruit was assessed in the strawberry field trials. The results of this study show that the use of AITC as a stand-alone treatment provided no consistent weed or pathogen control efficacy. However, our results also indicate that shank and drip applied multitactic fumigation approaches with AITC can efficiently control soil-borne diseases and weeds. These findings have potential implications, especially in those areas where certain fumigants are restricted due to regulations and/or availability.

Pest control with drip-applied dimethyl disulfide and chloropicrin in plastic-mulched tomato (Solanum lycopersicum L.).

Dimethyl disulfide (DMDS) is used as a preplant soil fumigant for weed and soilborne pathogen control in plasticulture vegetable crops. The objective of this research was to determine the control efficacy of emulsifiable concentrate (EC) formulation of DMDS or DMDS + chloropicrin (Pic) on weed and Fusarium wilt in tomato (Solanum lycopersicum L.) plasticulture. The effective DMDS rates required to provide 50% (ER50 ) control of purple nutsedge (Cyperus rotundus L.) were 210 and 340 kg ha-1 at 4 weeks after fumigation (WAF) in fall 2017 and fall 2018, respectively, while these values increased to 348 and >467 kg ha-1 , respectively, at 12 WAF. The ER50 values of DMDS + Pic were 150 and 240 kg ha-1 at 4 WAF in fall 2017 and fall 2018, respectively, while these values increased to 255 and 450 kg ha-1 , respectively, at 12 WAF. DMDS + Pic was generally more effective than DMDS for C. rotundus control. The high rates of DMDS or DMDS + Pic provided adequate C. rotundus control in early season but failed to provide effective control by season end. In addition, DMDS + Pic injections through drip tape effectively reduced Fusarium oxysporum f. sp. lycopersici (FOL) inoculum while DMDS alone was generally ineffective. Injection of the EC formulation of DMDS or DMDS + Pic through drip tape should have been provided a viable option for C. rotundus and Fusarium wilt control in plastic-mulched tomato. However, supplemental weed management actions, such as herbicide applications, may be required to achieve season-long control. © 2019 Society of Chemical Industry.

Evaluation of ethanedinitrile (EDN) as a preplant soil fumigant in Florida strawberry production.

Ethanedinitrile (EDN) has shown promising efficacy against weeds, plant-parasitic nematodes and soil-borne pathogens. Field experiments were conducted for three strawberry (Fragaria× ananassa D.) seasons in Balm and Dover, FL, USA to evaluate the control efficacy of EDN applied through drip tape on various weed species and the fungus Macrophomina phaseolina, the causal agent of charcoal rot of strawberry. Results revealed that 224, 336, 448 or 560 kg ha-1 EDN, and 104 kg ha-1 1,3-dichloropropene (1,3-D) + 176 kg ha-1 chloropicrin (Pic) applied through drip tapes under totally impermeable film were safe for strawberry production, with no adverse effect on strawberry growth and yield. EDN rates at 224, 336, 448 and 560 kg ha-1 were highly efficacious and equally effective in reducing purple nutsedge (Cyperus rotundus L.) in two of three growing seasons. Compared with the efficacy on purple nutsedge, the evaluated EDN rates were generally less effective on various broadleaf and grass weeds emerging on the bare ground and planting holes, but at 560 kg ha-1 consistently exhibited similar levels of control as 1,3-D + Pic. For M. phaseolina, the evaluated EDN rates were more efficacious than 1,3-D + Pic and significantly reduced inoculum buried in different bed locations in plastic-mulched beds. EDN has potential to be an efficacious tool for soil disinfestation and weed control in plasticulture strawberry production. © 2019 Society of Chemical Industry.

Impact of ethanedinitrile rates and application method on nutsedge species and tomato root galling

The pre-plant soil fumigant ethanedinitrile (EDN) has shown promising activity against several key pests including plant-parasitic nematodes, a variety of weeds, and soil-borne pathogens. With chemical properties similar to those of methyl bromide, EDN has the potential to move readily through the soil profile. EDN is being investigated as a pre-plant soil fumigant alternative to current industry standards for Florida plasticulture vegetable production. EDN was applied via shank injection, vapor, and drip irrigation. Control of nutsedge species and plant-parasitic nematode species was determined and compared to a non-treated control and a mixture of 39% 1,3-dichloropropene and 59.6% chloropicrin (1,3-D:Pic) in tomato and watermelon. In these studies, EDN performed as well as 1,3-D:Pic and significantly better than the nontreated control against nutsedge species. EDN applied as a vapor resulted in significantly increased nematode incidence at one location when compared with most other treatments.

Deep injection and the potential of biochar to reduce fumigant emissions and effects on nematode control

Reducing fumigant emissions is essential for minimizing the environmental impacts of pre-plant soil fumigation. Low permeability plastic films are effective at reducing emissions but have high initial purchase, installation, and disposal costs. The objective of this study was to evaluate if deep fumigant injection and biochar soil amendments can reduce emissions, improve fumigant distribution in soil, and provide acceptable control of plant parasitic nematodes. A pre-plant soil fumigation trial was conducted in a commercial orchard in the San Joaquin Valley, CA, USA. Treatments included two rates of Telone® C-35 (a mixture of 1,3-dichloropropene and chloropicrin) under totally impermeable film or with no surface seal, two injection depths (45 or 65 cm), and two biochar rates (20 or 40 ton ha−1). Emission rates were generally low due to rain events encountered during the trial, but data clearly showed that the deep injection enhanced fumigant delivery to depths below 60 cm and resulted in significantly lower peak emission compared to the standard injection depth. Biochar applied at 40 ton ha−1 had the lowest emission rates during 1-month monitoring period. Although variability in nematode survival was high, tarped, deep injection, and biochar treatment showed lower survival of nematodes at various depths. Increase in fumigant persistence, especially chloropicrin, was observed in this study, likely due to the high soil moisture and low temperature. All data indicate that biochar amendments can help reduce fumigant emissions without reducing nematode control; however, additional research is needed to optimize treatments, determine the affordability of various biochar materials, and validate results under a range of field conditions.

Anaerobic disinfestation induced changes to the soil microbiome, disease incidence and strawberry fruit yields in California field trials

Soil-borne disease management in California strawberry production systems has historically relied upon pre-plant soil fumigation. Restricted efficacy of currently available fumigant chemistries towards certain pathogens and regulatory action requiring increased buffer zones has stimulated interest in development of alternative disease control strategies. Anaerobic soil disinfestation (ASD) demonstrates activity toward an array of soil-borne pathogens, however, there exist limited field-scale trials examining efficacy in strawberry systems. Multiple mechanisms, including the activity of an altered soil microbiome, are reported to function in ASD-induced disease suppression but consistency of the microbial response across soils has not been examined. The present research reports ASD-induced changes in composition of the soil microbiome which occurred in a carbon input-dependent manner and were consistent in two of the three field trials conducted. At all three field sites, ASD treatments that transformed the microbiome were consistently associated with enhanced strawberry yields, but specific compositional attributes of the microbiome in effective treatments were not uniform among all sites. Enhanced yields were associated with control of specific soil-borne pathogens at a given site, however disease control was not uniformly attained across all pathogens resident to a given soil system. Findings demonstrate that informed selection of substrate to be used in ASD and knowledge of the targeted pathogen profile resident to the strawberry field soil will be essential to successful use of ASD in commercial agricultural production settings.

Efficacy of Anaerobic Soil Disinfestation for Control of Prunus Replant Disease.

Prunus replant disease (PRD) is an important soilborne complex that suppresses growth and productivity of replanted stone fruit and nut orchards. It is effectively managed with preplant soil fumigation but, due to regulatory challenges, nonfumigant-based control strategies for PRD and other soilborne disease problems may become increasingly important, especially in California. We examined the potential of preplant anaerobic soil disinfestation (ASD) for control of PRD in four repeated orchard replant trials on sandy loam soil near Parlier, CA. After removal of the old orchard trees, alternative ASD treatments, all using rice bran as the main carbon source, were implemented, starting in late September. The alternative treatments incorporated rice bran at (i) 20 t ha-1, alone, in 3.0-m-wide row strips; (ii) 20 t ha-1, preceded by incorporation of a sudangrass cover crop and followed by drip application of molasses (10 t ha-1), in 3.0-m-wide row strips; (iii) 20 t ha-1, alone, in 1.8-m-wide strips; or (iv) 12 t ha-1, alone, in 1.8-m-wide strips. All ASD-treated areas were covered with clear tarp and drip irrigated with 25 cm of water. Tarps remained for 6 weeks, during which the soil moisture level was kept at or above field capacity by drip irrigation. All trials included nontreated control and fumigated standard treatments. ASD raised temperature and reduced redox potential in soil at 15- and 46-cm depths for 6 weeks. Fumigation and ASD treatments both nearly eradicated bioassay inoculum of Pythium ultimum in the soil before almond trees were replanted and significantly affected almond tree root communities of fungi and oomycetes after planting. Fumigation treatments and ASD treatments with rice bran at 20 t ha-1 in 3.0-m strips increased tree growth significantly and by similar magnitudes. Among repeated experiments, mean increases in trunk cross-sectional area growth due to fumigation ranged from 137 to 264%, while the increases due to ASD at 20 t ha-1 in 3.0-m strips ranged from 148 to 214%, compared with controls. ASD offers effective control of PRD and is worthy of further optimization and testing for management of PRD and additional orchard replant problems.

Ecotoxicity of 1,3-dichloropropene, metam sodium, and dazomet on the earthworm Eisenia fetida with modified artificial soil test and natural soil test

1,3-Dichloropropene (1,3-D), metam sodium (MS), and dazomet (DZ) are widely used as preplant soil fumigants to solve soilborne problems. To provide a more scientific and accurate evaluation of 1,3-D, MS, and DZ toxicity to the earthworm Eisenia fetida, modified artificial soil test and natural soil test were studied. The suitable soil moisture to maintain over 90% survival of the earthworms after 4weeks of treatment in an enclosed system for modified artificial soil test and natural soil test were 26.9 to 86.4% of water-holding capacity (WHC) and 66.2 to 84.3% of WHC, respectively. The optimal soil moisture levels for modified artificial soil test and natural soil test (75 and 55% of WHC, respectively) were finally used to evaluate the toxicity of 1,3-D, MS, and DZ on earthworms. Each desiccator with 10 earthworms and natural or artificial soil was stored at 20±1°C under constant light of 400 to 800lx for 2weeks. The modified artificial soil test showed LC50 values for 1,3-D, MS, and DZ of 3.60, 1.69, and 5.41mg a.i. kg-1 soil, respectively. The modified natural soil test of the fumigants showed similar LC50 values of 2.77 and 0.65mg a.i. kg-1 soil, except for DZ at 0.98mg a.i. kg-1 soil. The present study confirms that both modified artificial soil test and modified natural soil test offer standard methods for acute toxicity test of 1,3-D, MS, and DZ on the earthworms and scientific evidences for assessing the effects of soil fumigants on non-target organisms in the soils. Graphical Abstract Two novel acute toxicity test methods for soil fumigants on the earthworm Eisenia fetida.