James S. Gerik

Effects of Manure and Water Applications on 1,3-Dichloropropene and Chloropicrin Emissions in a Field Trial

Minimizing fumigant emissions is required for meeting air-quality standards. Application of organic materials to surface soil has been effective in reducing fumigant emissions during laboratory tests, but the potential to reduce emissions in the field has not been adequately evaluated. The objective of this study was to determine the effect of incorporated composted manure with or without water applications on fumigant emissions and the potential impact on pest control efficacy under field conditions. Treatments included a bare-soil control, composted dairy manure at 12.4 and 24.7 Mg ha(-1), postfumigation intermittent water seals (11 mm water irrigated immediately following fumigation and 4 mm at 12, 24, and 48 h), and incorporation of manure at 12.4 Mg ha(-1) combined with the water seals or a high-density polyethylene (HDPE) tarp. Telone C35 was shank-applied at 553 kg ha(-1), and emissions of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) were monitored for 10 days. The results indicate that there was no significant difference in emission peak flux and cumulative emission loss between the control and the 12.4 Mg ha(-1) manure treatment. The higher manure rate (24.7 Mg ha(-1)) resulted in lower emission flux and cumulative emission loss than 12.4 Mg ha(-1), although the differences were only significant for CP. In contrast, the water treatments with or without manure incorporation significantly reduced peak emission rates (80% reduction) and cumulative emission loss ( approximately 50% reduction). The manure + HDPE treatment resulted in the lowest CP emissions but slightly higher 1,3-D emissions than the water treatments. Reductions in peak emission from water treatments can be important in reducing the potential acute exposure risks to workers and bystanders. This research demonstrated that incorporation of composted manure alone did not reduce fumigant emissions and effective emission reduction with manure amendment may require higher application rates and/or more effective materials than those used in this study.

Spot drip application of dimethyl disulfide as a post-plant treatment for the control of plant parasitic nematodes and soilborne pathogens in grape production.

BACKGROUND Plant parasitic nematodes and soilborne pathogens can reduce the overall productivity in grape production. Not all grape growers apply soil fumigants before planting, and there is no single rootstock resistant to all nematode species. The aim of this investigation was to evaluate the effect of dimethyl disulfide (DMDS) applied at 112, 224, 448 and 897 kg ha(-1) as a post-plant treatment against soilborne plant parasitic nematodes and pathogens on the grape yield in established grapevines. RESULTS In microplot and field trials, post-plant fumigation with DMDS controlled citrus (Tylenchulus semipenetrans), root-knot (Meloidogyne spp.), pin (Paratylenchus spp.) and ring (Mesocriconema xenoplax) nematodes in established Thomson Seedless grapevines. However, DMDS did not control the soilborne pathogens Pythium ultimum and Fusarium oxysporum. No indications of phytotoxicity were detected after post-plant fumigation with DMDS. In the field trial, grape yield was significantly higher with the lowest DMDS rate, but no difference among other rates was observed in comparison with the untreated control. CONCLUSION Post-plant fumigation with DMDS controlled plant parasitic nematodes in established grapevines but was less efficacious against soilborne pathogens. Low rates of DMDS were sufficient for nematode control and increased the grape yield, probably without affecting beneficial soil organisms. Further research on evaluating the potential effect of DMDS against beneficial soil organisms is needed.

Effects of reduced-rate methyl bromide applications under conventional and virtually impermeable plastic film in perennial crop field nurseries.

BACKGROUND Producers of perennial crop nursery stock in California use preplant soil fumigation to meet state phytosanitary requirements. Although methyl bromide (MB) has been phased out in many agricultural industries, it is still the preferred treatment in the perennial nursery industry and is used under Critical Use Exemptions and Quarantine/Preshipment provisions of the Montreal Protocol. The present research was conducted to evaluate reduced-rate MB applications sealed with conventional and low-permeability plastic films compared with the primary alternative material. RESULTS Reduced rates (100-260 kg ha(-1)) of MB applied in combination with chloropicrin (Pic) and sealed with a low-permeability plastic film provided weed and nematode control similar to the industry standard rate of 392 kg ha(-1) MB:Pic (98:2) sealed with high-density polyethylene (HDPE) film. However, the primary alternative chemical, 1,3-dichloropropene (1,3-D), tended to provide slightly lower pest control even on sites with relatively low plant parasitic nematode, soil-borne pathogen and weed pest pressure. CONCLUSION If California regulations change to allow the use of low-permeability films in broadcast fumigant applications, the results of this research suggest that reduced rates of MB in perennial crop nurseries could serve as a bridge strategy until more technically, economically and environmentally acceptable alternatives are developed.

Fumigation efficacy and emission reduction using low‐permeability film in orchard soil fumigation

BACKGROUND Many orchards use fumigation to control soilborne pests prior to replanting. Controlling emissions is mandatory to reduce air pollution in California. This research evaluated the effects of plastic film type [polyethylene (PE) or totally impermeable film (TIF)], application rate of Telone C35 [full (610 kg ha(-1) ), 2/3 or 1/3 rates] and carbonation at 207 kPa on fumigant transport (emission and in soil) and efficacy. RESULTS While increasing fumigant concentrations under the tarp, TIF reduced emissions >95% (∼2% and <1% of total applied 1,3-dichloropropene and chloropicrin respectively) relative to bare soil, compared with ∼30% reduction by PE. All fumigation treatments, regardless of film type, provided good nematode control above 100 cm soil depth; however, nematode survival was high at deeper depths. Weed emergence was mostly affected by tarping and fumigant rate, with no effects from the carbonation. CONCLUSION TIF can effectively reduce fumigant emissions. Carbonation under the studied conditions did not improve fumigant dispersion and pest control. The 2/3 rate with TIF controlled nematodes as effectively as the full rate in bare soil or under the PE film to 100 cm soil depth. However, control of nematodes in deeper soil remains a challenge for perennial crops.

Soil Microbial Community Structure and Target Organisms under Different Fumigation Treatments

Producers of several high-value crops in California rely heavily on soil fumigants to control key diseases, nematodes, and weeds. Fumigants with broad biocidal activity can affect both target and nontarget soil microorganisms. The ability of nontarget soil microorganisms to recover after fumigation treatment is critical because they play an important role in sustaining the health of agricultural and natural soil systems. Fumigation trial was conducted in Parlier, CA, and the study focuses on the effects of different rates of Telone C35 and also methyl bromide fumigation with polyethylene (PE) and totally impermeable film (TIF) tarps on target and nontarget soil microorganisms using field samples. Results indicated that the populations of target organisms, such as Fusarium oxysporum and Pythium spp., were reduced at all rates of fumigants. Phospholipid fatty acid (PLFA) analysis indicated that all major nontarget soil microbial groups such as Gram positive bacteria, Gram negative bacteria, fungi, and arbuscular mycorrhizal fungi (AMF) were affected by methyl bromide (MeBr) fumigation treatment. In general, the effects of Telone C35 (299 L/ha) under PE tarp had the least impact on microbial community structure and better effect on controlling target microorganisms and, therefore, indicated the better option among fumigation treatments.

Effects of surface treatments and application shanks on nematode, pathogen and weed control with 1,3-dichloropropene

BACKGROUND Preplant fumigation with methyl bromide (MeBr) has been used for control of soilborne pests in high-value annual, perennial and nursery crops, but is being phased out. In 2007 and 2008, research trials were conducted to evaluate the effects of surface treatments and two application shanks on pest control with 1,3-dicloropropene (1,3-D) in perennial crop nurseries. RESULTS All 1,3-D treatments controlled nematodes similarly to MeBr. Application of 1,3-D with virtually impermeable film (VIF) reduced Fusarium oxysporum compared with unfumigated plots, but was not as effective as MeBr. Applications of 1,3-D with VIF or 1,3-D followed by metam sodium reduced Pythium spp., but 1,3-D followed by intermittent water seals was comparable with the untreated plots. When sealed with high-density polyethylene (HDPE) film or VIF, 1,3-D generally was as effective as MeBr for reducing weed density and total weed biomass, but weed control was reduced by intermittent water seals and in unsealed plots subsequently re-treated with additional 1,3-D or metam sodium. CONCLUSION Applications of 1,3-D sealed with HDPE or VIF film or with intermittent water seals can control nematodes similarly to MeBr. However, additional management practices may be needed for effective pathogen and weed control if plastic film is not used.

Drip application of methyl bromide alternative chemicals for control of soilborne pathogens and weeds

BACKGROUND Producers of several high-value crops in California have traditionally used preplant soil fumigation with methyl bromide/chloropicrin combinations. Although methyl bromide has been phased out since 2005, several crop industries, including cut flower producers, have continued methyl bromide use under Critical Use Exemptions, a provision of the Montreal Protocol. This research was conducted to evaluate newer, emerging methyl bromide alternative chemicals. RESULTS Two field trials were conducted to test several emerging chemicals in combination with metam sodium as replacements for methyl bromide. Emerging chemicals included 2-bromoethanol, dimethyl disulfide, furfural, propylene oxide and sodium azide. Weed and pathogen populations were measured after chemical application, and seed viability was assessed from weed seed previously buried in the plots. In the first trial, the emerging chemicals did not improve pest control compared with metam sodium alone. However, in the second trial, several of these chemicals did improve the pest control performance of metam sodium. CONCLUSIONS The emerging alternative chemicals have the potential to provide better control of soilborne pathogens and weeds when used with metam sodium than metam sodium alone. Registration of these materials could provide California growers with a broader choice of tools compared with the limited methyl bromide alternatives now available.

Microbial community biomass and structure in saline and non-saline soils associated with salt- and boron-tolerant poplar clones grown for the phytoremediation of selenium

ABSTRACT Poplar trees (Populus spp.) are often used in bioremediation strategies because of their ability to phytoextract potential toxic ions, e.g., selenium (Se) from poor quality soils. Soil microorganisms may play a vital role in sustaining health of soil and/or tolerance of these trees grown in poor quality soils by contributing to nutrient cycling, soil structure, overall soil quality, and plant survival. The effect of naturally occurring salts boron (B) and Se on soil microbial community composition associated with poplar trees is not known for bioremediation strategies. In this study, three Populus clones 13–366, 345–1, and 347–14 were grown in spring 2006 under highly saline, B, and Se clay-like soils in the west side of the San Joaquin Valley (SJV) of CA, as well as in non-saline sandy loam soils located in the east side of the SJV. After 7 years of growing in the respective soils of different qualities, soil samples were collected from poplar clones grown in saline and non-saline soils to examine and compare soil quality effects on soil microbial community biomass and composition. The phospholipid fatty acid (PLFA) analysis was used to characterize microbial community composition in soils from trees grown at both locations. This study showed that microbial biomass and the amount and proportion of arbuscular mycorrhizal fungal (AMF) community were lower in all three poplar clones grown in saline soil compared to non-saline soil. Amounts of Gram + bacterial and actinomycetes PLFAs were significantly lower in poplar clone 13–366 grown in saline soil compared to non-saline soil; however, they did not differ significantly in poplar clones 347–14 and 345–1. Additionally, amounts of saprophytic fungal, Gram − bacterial and eukaryotic PLFA remained similar at saline and non-saline sites under poplar clones 347–14, 345–1, and 13–366. Therefore, this study suggested that salinity and B do have an impact on microbial biomass and AMF; however, these poplar clones still recycled sufficient amount of nutrients to support and protect saprophytic fungal and bacterial communities from the effects of poor quality soils.

Soil Microbial Community Composition in a Peach Orchard Under Different Irrigation Methods and Postharvest Deficit Irrigation

Abstract The San Joaquin Valley produces more than 250 unique crops and much of the U.S. fruits, vegetables, and nuts. One of the main limiting factors for production in this region is reduced availability of water. Deficit irrigation is a management practice where plants receive less than full irrigation but only at certain growth stages to minimize yield loss or long-term impacts to the crop. Given the multiple roles of soil microorganisms in the soil system, it is important to asses any impact of deficit irrigation on soil microbial communities. In the present study, full and deficit irrigation treatments were applied for 7 years using furrow, microsprinkler, and surface drip irrigation systems in a peach orchard. In the seventh year, soil samples were collected before and after implementation of deficit irrigation treatments to investigate effects on soil microbial community biomass and composition. Results showed that the proportion of Gram-positive bacteria and actinomycetes were significantly higher in furrow irrigation, whereas fungi and Gram-negative bacteria were lower in proportion under furrow irrigation as compared with microsprinkler and drip irrigation methods. Canonical variate analysis showed that soil microbial communities markedly differed after deficit treatment in furrow and microspray irrigation, but remained similar in surface drip irrigation in deficit and full irrigation. This may be due to frequent irrigation in surface drip where soil surface remained moist most of the time as compared with furrow and microsprinkler irrigation methods where irrigation was less frequent.