Meixia Guo

Evaluation of the combination of 1,3‐dichloropropene and dazomet as an efficient alternative to methyl bromide for cucumber production in China

BACKGROUND The combination of 1,3-dichloropropene (1,3-D) and dazomet (DZ) offers a potential alternative to methyl bromide (MB) for soil disinfection. MB is scheduled to be withdrawn from routine use by 2015 in developing countries. Combination treatments of 1,3-D + DZ were evaluated in a laboratory study and in two commercial cucumber fields. RESULTS Laboratory studies found that nearly all of the tested combinations of 1,3-D and DZ displayed positive synergistic activity on root-knot nematodes (Meloidogyne spp.), two major soilborne fungi (Fusarium spp. and Phytophthora spp.) and the seeds of two major weed species (Digitaria sanguinalis and Abutilon theophrasti). Field trials revealed that the combination of 1,3-D and DZ (at 10 + 25 g m(-2) ) successfully suppressed Meloidogyne spp. root galling, sharply reduced Fusarium spp. and Phytophthora spp. and maintained high cucumber yields. The combination treatment of 1,3-D + DZ was more effective than 1,3-D or DZ alone and provided results similar to methyl bromide with respect to pest control, plant mortality, plant height, yield and income. All of the treatments were significantly better than the non-treated control. CONCLUSION The results indicate that the tested combination of 1,3-D and DZ offers an efficient alternative to methyl bromide for cucumber production.

Evaluation of sulfuryl fluoride as a soil fumigant in China

BACKGROUND Root-knot nematodes and soil-borne diseases constrain the rapid development of protected agriculture in China, especially while phasing out methyl bromide (MB). The fumigant sulfuryl fluoride (SF) is currently used as an alternative to MB for the disinfestation of buildings and post-harvest commodities. Our experiments aimed to evaluate a novel application of SF as a soil fumigant in greenhouses in China. RESULTS Dose-response experiments indicated that SF has good efficacy on root-knot nematodes (Meloidogyne spp.) and moderate activity against Fusarium spp. and weeds (Digitaria sanguinalis (L.) Scop. and Abutilon theophrasti Medicus). The field trials indicates that SF has good efficacy, between 80 and 94%, on Meloidogyne spp., and Fusarium spp. at the rates of 25-50 g m(-2) in tomato and cucumber in Beijing and Shandong Province. Marketable yield and plant vigour was not significantly different in SF and MB treatments. SF has lower emissions than MB during the fumigation operation. It is simple to apply, can be used at low temperature, and has a short plant-back time. SF was found to be an economically feasible alternative to MB for nematode control in China. CONCLUSION SF can be used as a soil fumigant to control root-knot nematodes and to reduce the levels of key soil pathogens.

Evaluation of the Combination of Dimethyl Disulfide and Dazomet as an Efficient Methyl Bromide Alternative for Cucumber Production in China

The combination of dimethyl disulfide (DMDS) and dazomet (DZ) is a potential alternative to methyl bromide (MB) for soil disinfestation. The efficacy of DMDS plus DZ in controlling key soilborne pests was evaluated in a laboratory study and in two commercial cucumber greenhouses. Laboratory studies found that all of the combinations had positive synergistic effects on root-knot nematodes, two key soilborne fungi, and two major weed seeds. Greenhouse trials revealed that the combination of DMDS and DZ (30 + 25 g m(-2)) successfully suppressed Meloidogyne spp. root galling, sharply reduced the colony-forming units of Fusarium spp. and Phytophthora spp. on media, maintained high cucumber yields, and was not significantly different from MB or DMDS alone, but better than DZ alone. All of the chemical treatments provided significantly better results than the nontreated control. The results indicate that the combination of DMDS and DZ is an efficient MB alternative for cucumber production.

Quantification of Fusarium oxysporum in fumigated soils by a newly developed real-time PCR assay to assess the efficacy of fumigants for Fusarium wilt disease in strawberry plants.

BACKGROUND Two soil fumigants, chloropicrin (CP) and dimethyl disulfide (DMDS), were used to control Fusarium wilt disease (FWD) which caused large economic losses in strawberries. The fumigants were evaluated alone and in combination in a laboratory study and in strawberry greenhouses. RESULTS Laboratory tests found that combinations of CP and DMDS indicated a positive synergistic activity on Fusarium oxysporum. A newly developed quantitative assay for F. oxysporum involving real-time PCR was used successfully to evaluate F. oxysporum control by the fumigants; it provided similar results to the selective medium but was less time-consuming and less labor intensive. Greenhouse trials revealed that the combination of CP and DMDS successfully suppressed the incidence of FWD and sharply reduced the population density of F. oxysporum, which significantly increased fruit branch number and maintained a good strawberry yield, higher than methyl bromide (MB) treatment. All of the treatments provided significantly better results than the non-treated control. CONCLUSION This study confirms that the newly developed real-time PCR quantitative assay for F. oxysporum was suitable for the control efficacy evaluation of soil fumigants and that the novel fumigant combination of CP and DMDS offers a promising effective alternative to MB for the control of F. oxysporum in strawberry greenhouses.

Quantification of the effects of various soil fumigation treatments on nitrogen mineralization and nitrification in laboratory incubation and field studies

Better quantification of nitrogen mineralization and nitrification after fumigation would indicate if any adjustment is needed in fertilizer application. The effects of chloropicrin (Pic), 1,3-dichloropropene (1,3-D), dimethyl disulfide (DMDS) and metham sodium (MS) fumigation on soil nitrogen dynamics were evaluated in lab incubation and field studies. Although some differences were observed in NH(4)(+)-N and NO(3)(-)-N concentrations in lab incubation and field experiments, both studies led to the same conclusions: (1) Soil fumigation was shown to increase soil mineral nitrogen only during the first 2 weeks after fumigation (WAF). In particular, Pic significantly increased soil mineral nitrogen in both studies at 1 WAF. However, for all fumigant treatments the observed effect was temporary; the soil mineral content of treated samples recovered to the general level observed in the untreated control. (2) All the fumigation treatments depressed nitrification temporarily, although the treatments exhibited significant differences in the duration of nitrification inhibition. In both studies, for a limited period of time, Pic showed a stronger inhibitory effect on nitrification compared to other fumigant treatments. An S-shaped function was fitted to the concentrations of NO(3)(-)-N in lab incubation samples. The times of maximum nitrification (t(max)) in DMDS and MS treatments were 0.97 week and 1.03 week, which is similar to the untreated control (t(max)=1.02 week). While Pic has the longest effect on nitrifying bacteria, nitrification appears to restart at a later time (t(max)=14.37 week).

Emission reduction of 1,3-dichloropropene by soil amendment with biochar.

Soil fumigation is an important treatment in the production chain of fruit and vegetable crops, but fumigant emissions contribute to air pollution. Biochar as a soil amendment has shown the potential to reduce organic pollutants, including pesticides, in soils through adsorption and other physicochemical reactions. A laboratory column study was performed to determine the effects of soil applications of biochar for reducing emissions of the fumigant 1,3-dichloropropene (1,3-D). The experimental treatments comprised of unamended and amended with biochar at doses of 0, 0.5, 1, 2, and 5% (w/w) in the top 5 cm soil layer. The unamended treatment resulted in the highest emission peak flux at 48 to 66 μg m s. Among the biochar amendment treatments, the highest peak flux (0.83 μg m s) was found in the biochar 0.5% treatment. The total emission loss was 35.7 to 40.2% of applied for the unamended treatment and <0.1 to 2.9% for the biochar-amendment treatments. A germination bioassay with cucumber seeds showed that ≥7 d of aeration would be needed to avoid phytotoxicity before replanting in biochar-containing fumigated soil. The results indicate that treatments with 0.5% or more biochar amendment reduced emission peak flux by >99.8% and showed total 1,3-D emission loss by >92% compared with that without biochar. The amendment of surface soil with biochar shows a great potential for reducing fumigant emissions.

Evaluation of chloropicrin gelatin capsule formulation as a soil fumigant for greenhouse strawberry in China.

Gelatin capsules containing chloropicrin (Pic gel cap) were developed as a new formulation to reduce the potential human exposure risks associated with injection application methods. The objective of this study was to test the efficacy of a Pic gel cap formulation on soilborne pathogens and to determine the effects on strawberry plant growth and fruit yield. Three field experiments were conducted in strawberry greenhouses located in Mancheng County, China, in 2008-2010. The results demonstrated that effects of Pic gel cap on soilborne pathogens were similar to Pic injection; Pic gel cap effectively reduced key soilborne pathogens population, was partially effective against weeds, improved strawberry plant growth, and increased fruit yield significantly compared to the untreated control. Pic gel cap applied to preformed beds uses less fumigant than broadcast applications of Pic gel cap and can provide an equivalent level of disease control. The present study confirms that the Pic gel cap is a promising new formulation which provides field efficacy and marketable yields similar to Pic injection or methyl bromide in strawberry cultivation in China.

Evaluation of Chloropicrin as a Soil Fumigant against Ralstonia solanacarum in Ginger (Zingiber officinale Rosc.) Production in China

Background Chloropicrin (Pic) offers a potential alternative to methyl bromide (MB) against Ralstonia solanacarum in ginger (Zingiber officinale Rosc.) production. MB is scheduled to be withdrawn from routine use by 2015 in developing countries. Methods Pic treatments were evaluated in a laboratory study and in three commercial ginger fields. Results Laboratory studies showed that the EC50 value and EC80 value of Pic were 2.7 and 3.7 mg a.i. kg−1 soil, respectively. Field trials in highly infested soil revealed that treatments of Pic at the dose of 50 g m−2 covered with totally impermeable film (TIF) or polyethylene film (PE) sharply reduced Ralstonia solanacarum and maintained high ginger yields. Both of the Pic treatments provided results similar to, or in some cases slightly lower than, MB with respect to Ralstonia solanacarum control, plant survival, plant growth and yield. All of the fumigant treatments were significantly better than the non-treated control. Conclusions The present study confirms that the Pic is a promising alternative with good efficacy against Ralstonia solanacarum for ginger production and could be used in integrated pest management programs in China.

Chloropicrin Emission Reduction by Soil Amendment with Biochar.

Biochar has sorption capacity, and can be used to enhance the sequestration of volatile organic contaminants such as pesticides in soil. Chloropicrin (CP) is an important soil fumigant for the production of many fruit and vegetable crops, but its emissions must be minimized to reduce exposure risks and air pollution. The objective of this study was to determine the capacity of biochar to adsorb CP and the effect of biochar amendments to soil on CP emission, concentration in the soil gas phase, degradation in soil and CP bioactivity for controlling soil borne pests. CP emission and concentration in the soil air phase were measured from packed soil columns after fumigant injection at 20-cm depth and application of selected doses of biocharto the surface 5 cm soil. Laboratory incubation and fumigation experiments were conducted to determine the capacity of biochar to adsorb CP, the effects on CP degradation and, separately, CP’s bioactivity on soil borne pests in soil amended with biochar. Biochar amendment at 2% to 5% (w/w) greatly reduced total CP emission losses by 85.7% - 97.7% compared to fumigation without biochar. CP concentrations in the soil gas-phase, especially in the top 5 cm of soil, were reduced within 48 h following application. The half-life of CP decreased from 13.6 h to 6.4 h as the biochar rate increased from 0% to 5%. CP and its metabolite (dichloronitromethane) both degraded more rapidly in pure biochar than in soil. The biochar used in the present study had a maximum adsorption capacity for CP of less than 5 mg g-1. There were no negative effects on pathogen and nematode control when the biochar used in this study was less than 1% (on a weight basis) in soil. Biochar amendment to soil reduced the emissions of CP. CP concentrations in the top 5 cm of soil gas-phase were reduced. CP degradation was accelerated with the addition of biochar. The biochar used in the present study had a low adsorption capacity for CP. There were no negative effects on pathogen and nematode control when the biochar amendment rate was less than 1% (by weight). The findings would be useful for establishing guidelines for biochar use in soil fumigation.

1,3-Dichloropropene distribution and emission after gelatin capsule formulation application.

The gelatin capsule (gel cap) formulation of 1,3-dichloropropene (1,3-D) was developed as a potential means of reducing 1,3-D emissions. The objective of this study was to determine the distribution, emission, and leaching of 1,3-D after applying the gel cap in soil columns. Comparable 1,3-D soil gas concentrations were obtained between a conventional liquid injection control and the gel cap application with film treatment. When the soil surface was irrigated with 39.6 mm water per day during the first 4 days, 1,3-D soil gas concentration was higher than the film treatments at depths below 20 cm, but lower concentrations were observed at 0-15 cm depth. The application of 1,3-D gel cap relatively reduced total 1,3-D emission by about 41% compared to liquid injection with film cover, and total 1,3-D emission was only 0.13% for 1,3-D gel cap application with 4 days of irrigation without a tarp. The results indicated that 1,3-D gel cap could be a promising new technology for reducing environmental emissions and potential human exposure.