Chloropicrin Treatment Research Articles

Prevention and Control of Ginger Blast by Two Fumigants and Their Effects on a Soil Bacterial Community and the Metabolic Components of Ginger

A two-year field trial was conducted in order to assess techniques to control ginger blast and explore the effects of fumigants on soil bacterial microorganisms and ginger metabolites. This study examined the effects of dazomet and chloropicrin on the control of ginger blast and their influence on ginger yield in Luoping County, Yunnan Province, China. The results showed that in 2022, the control effectiveness of dazomet and chloropicrin treatments on ginger blast was 84.33% and 94.67%, respectively. The corresponding yields were 50,154.40 kg/hm2 and 50,296.90 kg/hm2. In 2023, the control effectiveness of dazomet and chloropicrin treatments on ginger blast were 86.33% and 93.67%, respectively, and the yields were 65,115.83 kg/hm2 and 65,337.93 kg/hm2. In both years, the incidence of ginger blast in the control group reached nearly 100%, leading to the near extinction of the crop. Additionally, in 2023, 16S rRNA high-throughput sequencing and non-targeted metabolomics techniques were used to analyze the effects of the fumigants on soil bacterial microorganisms and the metabolites in ginger. The results showed that the diversity and richness of soil bacterial communities were lower than those in the control group at 0 and 120 days after treatment with two fumigants, but the relative abundances of beneficial bacteria such as Pseudomonas increased at 60 days, and the relative abundances of Actinobacteria, Gemmatimonadetes, and Bacillus increased at 120 days. The abundance of Firmicutes also increased after 120 days of chloropicrin treatment. The non-targeted metabolic LC–MS results showed that the production of phenols and terpenoids was upregulated after dazomet and chloropicrin treatments. The contents of amino acids and their derivatives were also upregulated. This upregulation of metabolites was beneficial to the flavor quality of ginger and enhanced its anti-inflammatory, anti-tumoral, and antioxidant effects.

Insights for Soil Improvements: Unraveling Distinct Mechanisms of Microbial Residue Carbon Accumulation under Chemical and Anaerobic Soil Disinfestation

Soil disinfestation has been widely used as an effective strategy to improve soil health and crop yield by suppression of soil-borne plant pathogens, but its effect on soil organic carbon (SOC), a crucial factor linked to climate change, remains unknown. A microcosm trial was conducted to evaluate microbial residue carbon (MRC) and its contribution to SOC under chemical soil disinfestation (CSD) with quicklime (QL) and chloropicrin (CP), as well as anaerobic soil disinfestation (ASD) with maize straw (MASD) and soybean straw (SASD). The SOC concentrations were increased by both CSD and ASD. Also, total SOC-normalized MRC concentration was enhanced, with a considerable increase in soil bacterial and fungal MRC, particularly evident under CP and SASD treatment. Due to broad-spectrum biocidal activities, decreased SOC-normalized microbial biomass carbon (MBC) was consistent with the reductions in bacterial and fungal phospholipid fatty acids (PLFAs), consequently increasing MRC accumulation under CSD. Similarly, ASD decreased fungal PLFAs while shifting bacterial PLFAs from aerobic to anaerobic taxa or from gram-negative to -positive taxa, both of which contributed to both MBC and MRC buildup. Collectively, the findings demonstrate that ASD can efficiently increase SOC concentration, with distinct mechanisms underlying MRC generation when compared to traditional CSD.

A potential relationship between soil disinfestation efficacy and leaf green reflectance.

Soil disinfestation with steam was evaluated as an alternative to fumigation. Following soil disinfestation, plant health has traditionally been measured using plant size and yield. Plant health can be measured in a timely manner more efficiently, more easily and non-destructively using image analysis. We hypothesized that plant health could be quantified and treatments can be differentiated using an RGB (Red, Green, Blue) image analysis program, particularly by observing the greenness of plant leaves. However, plant size or the proportion of green area could be unreliable due to plant loss and camera's position and angle. To this end, we decided to evaluate plant health by analyzing the RGB codes associated with the green color only, which detects the chlorophyll reflectance and nutrient status, noting that the degree of greenness within the green-leaf-area was not affected by the plant size. We identified five RGB codes that are commonly observed in the plant leaves and ordered them from dark green to light green. Among the five RGB codes, the relative percentage covered by the darkest green to the lightest green was significantly different between the steam and chloropicrin treatments and the control, and it was not significantly different between the steam and chloropicrin treatments. Furthermore, the result was correlated with the total yield, and the trend observed in the first year was replicated in the second year of this experiment. In this study, we demonstrate that the RGB image analysis can be used as an early marker of the treatment effect on the plant health and productivity.

Evaluation of a Steam Application by a Mobile Applicator for Soil Disinfestation in Strawberry Nurseries

Soil disinfestation with steam has been evaluated in strawberry fruiting fields as a nonchemical method of soil disinfestation; however, little is known about the use of steam for field production of strawberry daughter plants. The objective of this study was to compare daughter plant production in soils previously treated with steam compared to those treated with standard methyl bromide (MB) and chloropicrin (Pic) treatments. A prototype field steam applicator and a self-propelled diesel-fueled steam generator and applicator were tested at two high-elevation nurseries near Macdoel, CA, in Sept. 2018 and Aug. 2020, respectively. The steam application heated the soil above 60 °C for ≈60 minutes to a depth of 25 cm at both nurseries. The pest control efficacy of the steam applications against weeds, Verticillium spp., Tylenchulus semipenetrans, and Pythium ultimum were similar to that of MB:Pic. The stolons and daughter plants densities in fields with steam treatment were similar to those in fields with MB:Pic treatment. Therefore, we suggest that soil disinfestation with steam may be a viable method of producing healthy strawberry plants. However, more research is needed to verify plant sanitation and quality.

A reassessment of the fungicidal efficacy of 1,3-dichloropropene, chloropicrin, and metam potassium against Macrophomina phaseolina in strawberry.

The effectiveness of metam potassium, 1,3-dichloropropene, chloropicrin, and different ratios of 1,3-dichloropropene and chloropicrin on the reduction of natural and artificial inoculum of Macrophomina phaseolina were investigated in laboratory and field experiments. Additionally, a multivariate meta-analysis with data from six field trials conducted in Florida from 2012 to 2018 was performed. In small-plot field experiments using drip stakes, the highest rate (468 L ha-1 ) of metam potassium was most effective in controlling M. phaseolina in infected crowns buried at 15.2cm from the point of fumigant injection, whereas none of the rates was able to reduce inoculum buried at 30.5cm. In closed-container experiments, use of the highest rate of 1,3-dichloropropene (168 kg ha-1 ) resulted in the highest level of pathogen control. Different rates of chloropicrin also reduced inoculum when compared to the non-treated control. 1,3-dichloropropene + chloropicrin at different ratios were also highly effective in controlling M. phaseolina. Results from the meta-analysis of open-field experiments indicated that metam potassium and 1,3-dichloropropene + chloropicrin (63:35, v:v) treatments were significantly more effective in reducing M. phaseolina than the 1,3-dichloropropene + chloropicrin (39:60, v:v) treatment; however, metam potassium was not as effective at the side of the beds. 1,3-dichloropropene alone and in mixture with chloropicrin were more effective in reducing inoculum of M. phaseolina than chloropicrin alone, indicating the fungicidal efficacy of 1,3-dichloropropene. Formulation with higher 1,3-dichloropropene concentration performed better than the formulation with higher chloropicrin concentration in field trials. Metam potassium was effective when applied at the highest rate, but with limited lateral movement perpendicular to the drip irrigation line. © 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.

Effects of chloropicrin fumigation on soil and growth and development of Panax notoginseng

The continuous cropping obstacle of Panax notoginseng is serious, and effective control measures are lacking. Soil disinfection with chloropicrin(CP) has been proven to be effective in reducing the obstacles to continuous cropping of other crops. In order to ascertain the effect of CP in the continuous cropping of P. notoginseng, this paper explored the influences of CP at different treatment concentrations(0,30,40,50 kg/Mu, 1 Mu≈667 m~2) on soil macro-element nutrients, soil enzyme activity, growth and development of P. notoginseng, and the accumulation of medicinal components. The results showed that CP fumigation significantly increased the content of total nitrogen, alkali-hydrolyzable nitrogen, ammonium nitrogen, nitrate nitrogen, and available phosphorus in the soil, but it had no significant effect on potassium content. The soil protease activity showed a trend of first increasing and then decreasing with the prolonging of the treatment time. Both the soil urease and acid phosphatase activities showed a trend of first decreasing and then increasing with the prolonging of the treatment time. The higher the CP treatment concentration was, the lower the urease and acid phosphatase activities would be in the soil. The protease activity was relatively high after CP40 treatment, which was better than CP30 and CP50 treatments in promoting the nitrogen-phosphorus-potassium accumulation in P. notoginseng. The seedling survival rates after CP0, CP30, CP40, and CP50 tratments in October were 0, 65.56%, 89.44%, and 83.33%, respectively. Compared with the CP30 and CP50 treatments, CP40 treatment significantly facilitated the growth and development of P. notoginseng, the increase in fresh and dry weights, and the accumulation of root saponins. In summary, CP40 treatment accelerates the increase in soil nitrogen and phosphorus nutrients and their accumulation in P. notoginseng, elevates the seedling survival rate of P. notoginseng, enhances the growth and development of P. notoginseng, and promotes the accumulation of medicinal components. CP40 treatment is therefore recommended in production.

Fresh chicken manure fumigation reduces the inhibition time of chloropicrin on soil bacteria and fungi and increases beneficial microorganisms

Chloropicrin (CP) controls soil-borne plant diseases caused by pathogenic microbes, increases crop yield, but has a long-term inhibitory effect on beneficial soil microorganisms. Therefore, we evaluated the effects of biofumigation material fresh chicken manure (FCM) on soil microorganisms, and the duration of those effects in this experiment. Our results showed that in the laboratory, FCM significantly increased substrate-induced respiration (SIR) of soil microorganisms by 2.2–3.2 times at 80 d compared to the control, however, CP significantly inhibited the SIR of soil microorganisms. FCM and CP increased NH4+-N concentration within 40 days which then returned to the control level. FCM increased NO3--N by 2.82–5.78 times by 80 days, compared with the control, while the concentration of NO3--N in the CP treatment was not significantly different from the control at the 80 day. Although in the laboratory FCM inhibited the relative abundance of 16 S rRNA and the nitrogen cycle functional genes AOA amoA, AOB amoA, nirK and nosZ over a 40-day period, the taxonomic diversity of soil bacteria and fungi in the FCM treatment were restored to unfumigated level within 90 days in the field. However, CP treatment has a strong inhibitory effect on soil microorganisms after 90 days. Importantly, the relative abundance of some beneficial microorganisms that control soil-borne pathogenic microbes or degrade pollutants increased significantly in FCM, including Bacillus, Pseudomonas and Streptomyces bacterial genera and Chaetomium and Mycothermus fungal genera. Noteworthy, like CP, FCM still had a strong inhibitory effect on Fusarium at 90 d. Our results indicated that FCM not only increased the content of inorganic nitrogen and improved the respiration rate of soil microorganisms, but it also shortened the recovery time of beneficial soil microorganisms and increased taxonomic diversity. Our previous reports showed that FCM and CP treatments had the same effect in disease control and crop growth. Combined with the results of this experiment, we believe that FCM has the potential to replace CP, which would eliminate CP's detrimental environmental impact, improve farmer safety and promote sustainable crop production.

Effect of fresh chicken manure as a non-chemical soil fumigant on soil-borne pathogens, plant growth and strawberry fruit profitability

We investigated the ability of fresh chicken manure (FCM) to control pathogens, to promote strawberry plant growth, strawberry yield and farmer income. Laboratory tests showed that FCM inhibited the growth of Fusarium oxysporum, Pestalotiopsis spp., Phytophthora infestans and Rhizoctonia solani, and root-knot nematode (Meloidogyne spp.). Although the CFU of Fusarium spp. and Phytophthora spp. in FCM was higher than in the chloropicrin (CP) treatment, it was significantly lower than in the control. Additionally, FCM and CP both promoted the growth of strawberry plants in laboratory tests. In field tests and compared with control, FCM and CP significantly reduced Fusarium spp. and Phytophthora spp. by 95.71% & 98.89% and 78.06% & 94.81%, respectively. FCM increased chlorophyll in strawberry plant leaves and promoted plant growth, compared with control and CP. Field-applied FCM also increased the content of NO3−-N, available P, K and organic matter, lowered soil pH, increased strawberry marketable yield (20.99%) and farmers' income (21.58%), compared with control. In addition, compared with control, FCM increased strawberry fruits soluble sugar and ascorbic acid content by 14.33% and 73.41%, respectively, and significantly decreased titratable acidity, which are known to contribute to improvement in fruit taste. In addition, FCM as a fumigant is readily available cheaper than chemical fumigants. Fresh chicken manure therefore has the potential to be an effective, environmentally-friendly alternative to chemical fumigants. The use of FCM reduces both environmental pollution from animal waste and the use of chemical fumigants, thereby contributing to China's goal of not increasing the use of chemical fertilizers and pesticides.

Evaluation of Broadcast Steam Application with Mustard Seed Meal in Fruiting Strawberry

Soil disinfestation with steam has potential to partially replace fumigants such as methyl bromide, chloropicrin, and 1,3-dichloropropene because it is effective, safer to apply, and has less negative impact on the environment. Here, we compared the efficacy of steam and steam + mustard seed meal (MSM) to chloropicrin on soil disinfection, plant growth, and fruit yield in a strawberry (Fragaria ×ananassa) fruiting field. The MSM was applied at 3368 kg·ha−1 before the steam application. Steam was injected into a 3-m-wide reverse tiller that was set to till 30 to 40 cm deep. Soil temperatures at depths of 10, 20, 25, and 35 cm were monitored. Steam and steam + MSM treatments reduced the viability of purslane seeds and nutsedge tubers, microsclerotia density of Verticillium dahliae, propagule density of Pythium ultimum, cumulative weed densities, and biomass compared with the nontreated control. Moreover, the steam application was as efficacious as chloropicrin on these pests. The growth and fruit yield of strawberries grown on soils previously treated with the steam and steam + MSM treatments were similar to those in the chloropicrin treatment and were higher than those in the nontreated control. Our study indicated that steam, steam + MSM, and chloropicrin are equally effective at suppressing weeds and soilborne pathogens. These results suggest that the steam and steam + MSM treatment can be a practical alternative for soil disinfestation in conventional and organic strawberry fields.

Contrasting resilience of soil microbial biomass, microbial diversity and ammonification enzymes under three applied soil fumigants

Fumigation is a widely applied approach to mitigate the soil-borne diseases. However, the potential effects of currently applied fumigants on ammonification remain unclear. An 84-day incubation experiment was conducted based on non-fumigated soil (CK) and fumigated soil using three common fumigants, i.e., chloropicrin (CP), 1,3-dichloropropene (1,3-D), and metam sodium (MS). The results showed that, the three fumigants all decreased the microbial C, and the largest reduction (84.7%) occurred with the application of CP. After fumigation, the microbial diversity in the CP treatment rapidly recovered, but that in the 1,3-D treatment decreased and did not recover by the end of the experiment. The application of MS showed no impact on the microbial diversity during the assay, indicating that significantly different microbial diversity can be achieved by choosing different fumigants. Furthermore, the three fumigants showed divergent effects on the enzymes involved in ammonification. The analysis showed that the enzyme variation with CP application was mainly associated with the changed microbial C and N (P<0.05), and not with the microbial community, which was different from the observed effects of 1,3-D or MS application. In addition, the soil quality index showed that CP was still significantly harmful at the end of incubation compared with the good resilience of MS, indicating that CP may not be a suitable fumigant.

Transcriptomic Analysis of Human Primary Bronchial Epithelial Cells after Chloropicrin Treatment.

Chloropicrin is a vaporizing toxic irritant that poses a risk to human health if inhaled, but the mechanism of its toxicity in the respiratory tract is poorly understood. Here, we exposed human primary bronchial epithelial cells (HBEpC) to two concentrations of chloropicrin (10-50 μM) for 6 or 48 h and used genomic microarray, flow cytometry, and TEM-analysis to monitor cellular responses to the exposures. The overall number of differentially expressed transcripts with a fold-change > ± 2 compared to controls increased with longer exposure times. The initial response was activation of genes with a higher number of up- (512 by 10 μM and 408 by 40 μM chloropicrin) rather than down-regulated transcripts (40 by 10 μM and 215 by 40 μM chloropicrin) at 6 h seen with both exposure concentrations. The number of down-regulated transcripts, however, increased with the exposure time. The differentially regulated transcripts were further examined for enriched Gene Ontology Terms (GO) and KEGG-pathways. According to this analysis, the "ribosome" and "oxidative phosphorylation" were the KEGG-pathways predominantly affected by the exposure. The predominantly affected (GO) biological processes were "protein metabolic process" including "translation," "cellular protein complex assembly," and "response to unfolded protein." Furthermore, the top pathways, "NRF2-activated oxidative stress" and "Ah-receptor signaling," were enriched in our data sets by IPA-analysis. Real time qPCR assay of six selected genes agreed with the microarray analysis. In addition, chloropicrin exposure increased the numbers of late S and/or G2/M-phase cells as analyzed by flow cytometry and induced autophagy as revealed by electron microscopy. The targets identified are critical for vital cellular functions reflecting acute toxic responses and are potential causes for the reduced viability of epithelial cells after chloropicrin exposure.

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

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

The effects of methyl bromide alternatives on soil and seedling pathogen populations, weeds, and seedling morphology in Oregon and Washington forest nurseries

Five fumigation treatments (a conventional methyl bromide – chloropicrin application and four reduced-rate alternative fumigant treatments) and a nonfumigated treatment were evaluated at two forest nurseries in Oregon and one forest nursery in Washington for their effects on soil pathogen populations, weeds, and seedling morphology during a 2-year study. The effect of plastic tarp composition on fumigant efficacy was also evaluated (virtually impermeable film versus high-density polyethylene). All fumigant treatments reduced soil populations of Fusarium and Pythium for up to 7 months after fumigation and resulted in seedlings with significantly less pathogen colonization than those from the nonfumigated treatment. All fumigant treatments were more effective against pathogen inoculum buried at 15 cm rather than at 30 cm. Fusarium commune Skovgaard, O’Donnell et Nirenberg, Fusarium oxysporum Schlect. emend. Snyder &amp; Hansen, isolates from the Gibberella fujikuroi Saw. complex, Pythium irregulare Buisman, Pythium aff. spiculum B. Paul 2006, Pythium sylvaticum Campbell &amp; Hendrix, and Pythium ‘vipa’ Hermansen &amp; Klemsdal were the most commonly isolated pathogens. Weed biomass and weeding times were significantly reduced by fumigation, but only at the Washington nursery with high weed pressure. No significant differences were observed in efficacy between the conventional methyl bromide – chloropicrin treatment and any of the reduced rate fumigants or between the two types of plastic tarp. Conifer seedling height, diameter, shoot volume, and root volume were significantly greater in all fumigated treatments compared with the nonfumigated treatment.

Effects of Fumigant Alternatives to Methyl Bromide on Pest Control in Open Field Nursery Production of Perennial Fruit and Nut Plants

Nursery producers of perennial fruit and nut plants rely on preplant fumigation to meet regulatory requirements designed to ensure nematode-free planting stock. In the past, preplant treatments with methyl bromide or high rates of 1,3-dichloropropene were the preferred treatments. However, the phase out of methyl bromide due to environmental concerns and evolving regulations on the use of 1,3-dichloropropene has increased the need for effective and economical alternative fumigation treatments in open field nursery production. A field trial was conducted in a commercial nursery to test weed and nematode control with several tarped and untarped preplant applications of 1,3-dichloropropene, chloropicrin, and iodomethane in comparison with methyl bromide. Crop safety and nematode infestation were evaluated on a wide range of tree, vine, and berry nursery stock. No fall fumigation treatment in this study resulted in measurable injury to spring-planted nursery stock. There were few statistical differences between methyl bromide and the other fumigation treatments in crop establishment, crop quality, or nematode level at planting 5 months after treatment, although some untarped treatments had detectable levels of the root-knot nematode (Meloidogyne spp.). At grape (Vitus vinifera) and bramble (Rubus spp.) harvest after the first growing season, few statistical differences were noted in the number of nematodes isolated from roots; however, only methyl bromide had nondetectable levels in all varieties. The highest nematode levels were usually found in untarped iodomethane:chloropicrin and untarped chloropicrin plots. At tree harvest 26 months after fumigation, root-knot nematodes were isolated from the roots of highly susceptible tree varieties in several iodomethane:chloropicrin treatments and in chloropicrin alone plots. Untarped applications did not provide commercially acceptable control of weeds or root-knot nematode in this trial. Tarped applications of 30:70 and 50:50 iodomethane:chloropicrin provided nematode control similar to 1,3-dichloropropene, although not as good as methyl bromide. Iodomethane:chloropicrin combinations have been registered in other states and should be considered for use in California perennial fruit and nut crop nurseries as an alternative to methyl bromide.

Effects of Fumigant Alternatives to Methyl Bromide on Pest Control in Open Field Nursery Production of Perennial Fruit and Nut Plants

Nursery producers of perennial fruit and nut plants rely on preplant fumigation to meet regulatory requirements designed to ensure nematode-free planting stock. In the past, preplant treatments with methyl bromide or high rates of 1,3-dichloropropene were the preferred treatments. However, the phase out of methyl bromide due to environmental concerns and evolving regulations on the use of 1,3-dichloropropene has increased the need for effective and economical alternative fumigation treatments in open field nursery production. A field trial was conducted in a commercial nursery to test weed and nematode control with several tarped and untarped preplant applications of 1,3-dichloropropene, chloropicrin, and iodomethane in comparison with methyl bromide. Crop safety and nematode infestation were evaluated on a wide range of tree, vine, and berry nursery stock. No fall fumigation treatment in this study resulted in measurable injury to spring-planted nursery stock. There were few statistical differences between methyl bromide and the other fumigation treatments in crop establishment, crop quality, or nematode level at planting 5 months after treatment, although some untarped treatments had detectable levels of the root-knot nematode (Meloidogyne spp.). At grape (Vitus vinifera) and bramble (Rubus spp.) harvest after the first growing season, few statistical differences were noted in the number of nematodes isolated from roots; however, only methyl bromide had nondetectable levels in all varieties. The highest nematode levels were usually found in untarped iodomethane:chloropicrin and untarped chloropicrin plots. At tree harvest 26 months after fumigation, root-knot nematodes were isolated from the roots of highly susceptible tree varieties in several iodomethane:chloropicrin treatments and in chloropicrin alone plots. Untarped applications did not provide commercially acceptable control of weeds or root-knot nematode in this trial. Tarped applications of 30:70 and 50:50 iodomethane:chloropicrin provided nematode control similar to 1,3-dichloropropene, although not as good as methyl bromide. Iodomethane:chloropicrin combinations have been registered in other states and should be considered for use in California perennial fruit and nut crop nurseries as an alternative to methyl bromide.

Evaluation of Fumigants, EPTC Herbicide, and Paenibacillus macerans in the Production of Loblolly Pine Seedlings

Abstract Chloropicrin fumigation, Eptam 7-E (EPTC) herbicide, and Paenibacillus macerans seed treatments were evaluated as alternatives to fumigation with methyl bromide/chloropicrin for loblolly pine (Pinus taeda L.) seedling production at three nurseries in the southern United States. A treatment of metam sodium/chloropicrin was also evaluated at one nursery. Seedling density was unaffected by fumigation and EPTC treatments at all nurseries. Seedling diameter and shoot weight were greater in some chloropicrin treatments during the first year at the southern Georgia nursery. The only measurable disease losses were caused by a nematode, Longidorus americanus, at the southern Georgia nursery. Soil-borne population densities of Pythium and Fusarium spp. did not significantly differ between methyl bromide and the other fumigant treatments at any nursery. Chloropicrin controlled nutsedge (Cyperus spp.) in the loamy sand soils at the southern Georgia nursery, but there were no differences between the control and the fumigant treatments at the Alabama nursery, and nutsedge was rarely found at the northern Georgia nursery. The herbicide EPTC had no effect on nutsedge when compared to the controls at all nurseries and the effects of the bacterial seed treatment were inconsistent among the nurseries. Chloropicrin and metam sodium/chloropicrin can be effective alternatives to methyl bromide for reducing soil-borne fungi and nematodes, but the effectiveness of chloropicrin for nutsedge control may be affected by soil type.

Application of chloropicrin to Douglas-fir stumps to control laminated root rot does not affect infection or growth of regeneration 16 growing seasons after treatment

Phellinus weirii (Murr.) Gilb. causes laminated root rot (LRR), a major disease affecting growth and survival of Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir) and other commercially important conifer species throughout the Pacific Northwest. This disease is known to spread to a replacement stand by root contact between replacement trees and residual infected stumps and roots from the harvested stand. One strategy to manage LRR is to reduce the residual inoculum on a site through application of a fungicidal chemical to infested stumps. The first two studies in this series established that chloropicrin (trichloronitromethane), applied to infested stumps, largely eliminates P. weirii from most of the belowground biomass and determined the effective dosage to apply. This third study approximated an operational application and based treatment success on reduction of LRR in the replacement stand. The study area was an 8-ha, 65-year-old naturally regenerated second-growth stand that was predominantly Douglas-fir. The stand was surveyed preharvest and postharvest (clearcut). Each P. weirii-infected entity (standing dead or down trees and stumps) was marked, and the location of its center was mapped. Circular plots (0.04 ha) were located so as to include concentrations of infested stumps. Plots were stratified based on their estimated biomass of inoculum into eight replicate blocks of four plots each. Three chloropicrin treatments and an untreated control were assigned randomly to four plots in each of the eight blocks: (a) 100% labeled dosage to all stumps, (b) 20% labeled dosage to all stumps, (c) 100% labeled dosage to only visibly P. weirii-infected (stump-top stain or advanced decay) stumps, and (d) control (nothing done to the stumps). Holes were drilled into stump tops, a dose of chloropicrin poured in, and the holes plugged. The labeled dosage was 3.3 ml of chloropicrin per kilogram of estimated stump and root biomass. Douglas-fir seedlings were planted in the winter following treatment application. When the stand was considered established, each plot was thinned to an inter-tree spacing of 2.4 m and the trees tagged. Diameter at breast height, total height, and mortality of trees were recorded every 2–5 years. A total of 1041 tagged trees were observed for 16 growing seasons following treatment. Application of chloropicrin to stumps in the harvested stand did not influence the rate of LRR-caused mortality or growth of Douglas-fir seedlings in the replacement stand.

DNA- versus RNA-based denaturing gradient gel electrophoresis profiles of a bacterial community during replenishment after soil fumigation

We compared the responsiveness and sensitivity to soil fumigation of DNA- and RNA-based analyses of a bacterial community. We first established an improved RNA extraction method using DNA as an adsorption competitor, because it is extremely difficult to extract nucleic acids from clay-rich volcanic ash soil (Andisol), which adsorbs nucleic acids. This novel method facilitated RNA extraction from 500 mg of Andisol for molecular analyses. Then we monitored 16S rDNA PCR and 16S rRNA RT-PCR denaturing gradient gel electrophoresis (DGGE) profiles of samples collected from a chloropicrin (CP)-treated field over 2 months. The difference between untreated control and CP-treated plots was detected clearly both in DNA- and RNA-based DGGE profiles after treatment. The temporal changes in DGGE profiles, however, differed between DNA- and RNA-based analyses in CP-treated plots. RNA-based DGGE showed quicker and greater changes in the bacterial community after CP treatment than did DNA-based DGGE, which showed similar trends to RNA-based DGGE but with a time lag. The extent of decrease in the diversity index ( H′) and the change in principal response curves was larger in RNA-based analyses. These results indicate that the rDNA PCR-DGGE method also detects DNA of microbes no longer alive after fumigation, and that rRNA provides a more responsive biomarker than rDNA.

Drip-applied Soil Fumigation for Freesia Production

Field trials were conducted to test fumigants as alternatives to methyl bromide (MB) for production of hybrid freesia (Freesia × hybrida). One trial compared rates of 1,3-dichloropropene (DP) combined with chloropicrin (CP); the second trial compared iodomethane (IM) together with CP, DP:CP, and furfural with and without metham sodium; and the third trial compared rates and formulations of IM:CP to the standard MB:CP treatments. Most treatments reduced populations of Pythium spp. and controlled weeds compared to the untreated controls. Formulations of IM:CP reduced the incidence of disease caused by Fusarium oxysporum. Treatments of IM:CP performed as well as MB:CP, and treatments of DP:CP performed as well as IM:CP. Presently only the DP, CP and metham sodium formulations are registered for use on ornamental crops. Registration of the IM formulations will improve the options available to cut flower growers for management of plant pathogens and weeds.