Metam Research Articles

Evaluation of Soil Fumigants Applied by Drip Irrigation for Liatris Production.

Cut-flower growers need alternatives to methyl bromide (MB) for pathogen and weed control. The efficacy of alternative chemicals applied by drip irrigation was tested in a cut-flower production system. In 2002, seven chemical formulations were tested: chloropicrin, iodomethane + chloropicrin, 1,3-dichloropropene + chloropicrin, sodium azide, metham sodium, furfural + allyl isothiocyanate, and furfural + metham sodium. In 2003, an additional treatment, dimethyl disulfide, was added. Most treatments reduced populations of Pythium ultimum and Fusarium oxysporum and increased stem height compared with the nontreated controls. Metham sodium, furfural + metham sodium, sodium azide, and chloropicrin significantly reduced incidence of Liatris stem rot caused by Sclerotinia sclerotiorum. Weed control was not acceptable either year for any treatments. Viable alternatives to MB for cut-flower production will require better treatments for weed control than was achieved in this study.

Effects of Dazomet, Metam Sodium, and Oxamyl on Longidorus Populations and Loblolly Pine Seedling Production

Abstract Dazomet, metam sodium, and oxamyl were evaluated for nematode control and production of loblolly pine seedlings in a field infested by a Longidorus sp. Fumigation with dazomet or metam sodium reduced population densities of Longidorus to nondetectable levels early in the growing season but population densities subsequently increased to levels found in untreated control plots by the end of the growing season. Oxamyl had no effect on Longidorus population densities. Seedlings in dazomet-treated plots had significantly greater root and shoot weights than seedlings in control and oxamyl-treated plots within 6 weeks of seed sowing. At the end of the growing season, seedlings in the control and oxamyl plots were very stunted with poorly developed root systems. Seedling shoot length and root collar diameter in dazomet-treated plots averaged 27.4 cm and 4.0 mm, respectively, but in nonfumigated control plots these variables averaged 10.5 and 2.5 mm, respectively. Although dazomet and metam sodium were effective in reducing Longidorus populations for the first seedling crop after fumigation, production of a second crop without additional treatment would be inadvisable based on the increased population of Longidorus by the end of the first growing season. South. J. Appl. For. 29(3):117–122.

Alternative Soil Solarization Treatments for the Control of Soil‐borne Diseases and Weeds of Strawberry in the Western Anatolia of Turkey

AbstractField experiments were conducted in the two cropping seasons between 2002 and 2004 to determine effects on soil‐borne diseases, weeds and yield of strawberry of raised bed solarization (RBS), alone or with chicken manure (CM) amendment, methyl bromide (MB), TeloDrip (1,3‐dichloropropene + chloropicrin), short RBS combined with reduced doses of metam sodium (MS) and TeloDrip. In both seasons, raised bed soil solarization (for 7 weeks) alone or with CM amendment (10 t/ha), MS (50 ml/m2) after 2‐week RBS, and MB (50 g/m2) significantly reduced soil‐borne diseases (caused by Rhizoctonia spp. and Phytophthora cactorum) while application of TeloDrip at a rate of 500 kg/ha and a half‐dose after short solarization controlled the soil‐borne diseases to a lesser extent in the 2003–2004 cropping season. All treatments provided effective control of four weed species; annual bluegrass (Poa annua), common purslane (Portulaca oleracea), redroot pigweed (Amaranthus retroflexus) and barnyardgrass (Echinochloa crus‐galli) but not horseweed (Conyza canadensis). In the first year trial, total marketable yields from RBS with or without CM and 2‐week solarization plus MS were equivalent to yields produced by MB treatment whereas only raised bed soil solarization and CM amendment led to the same increase of yield as MB in the second year.

Biofumigation and Soil Conditioning Effects of Cover Crops in Processing Tomato

Mustard cover crop residue has been reported to have a “biofumigant” action when incorporated into the soil, potentially providing significant disease suppression and yield improvement for the succeeding crop. Such activity could be particularly useful in processing tomato rotations, where consecutive cropping invariably results in yield decline. Agronomic and environmental effects of growing over-winter mustard cover crops preceding tomato production were investigated in three field trials between 2002 and 2004. Two mustard cover crops [`Pacific Gold', a brown mustard (Brassica juncea), and `Caliente', a blend of brown and white mustard (Sinapis alba)] were compared to a legume cover crop mix, a fallow bed treatment (the standard grower practice in this region), and, in two of the three trials, a fumigation treatment using metam sodium. No suppression of soil populations of Verticillium dahliae or Fusarium spp. was observed with the mustard cover crops, nor was there any visual evidence of disease suppression on subsequent tomato crops. In these fields, the mustard either had no effect, or reduced tomato yield, when compared to the fallow treatment. At one of two sites, metam sodium fumigation significantly increased tomato yield. The presence of a cover crop, whether mustard or legume, reduced winter runoff by an average of 50% over two years of trials. No benefit of mustard cover cropping beyond this reduction in winter runoff was observed.

Sodium Methyldithiocarbamate Inhibits MAP Kinase Activation through Toll-like Receptor 4, Alters Cytokine Production by Mouse Peritoneal Macrophages, and Suppresses Innate Immunity

Sodium methyldithiocarbamate (SMD; trade name, Metam Sodium) is an abundantly used soil fumigant that can cause adverse health effects in humans, including some immunological manifestations. The mechanisms by which SMD acts, and its targets within the immune system are not fully understood. Initial experiments demonstrated that SMD administered by oral gavage substantially decreased IL-12 production and increased IL-10 production induced by lipopolysaccharide in mice. The present study was conducted to further characterize these effects and to evaluate our working hypothesis that the mechanism for these effects involves alteration in signaling through toll-like receptor 4 and that this would suppress innate immunity to infection. SMD decreased the activation of MAP kinases and AP-1 but not NF-kappaB in peritoneal macrophages. The expression of mRNA for IL-1alpha, IL-1beta, IL-18, IFN-gamma, IL-12 p35, IL-12 p40, and macrophage migration inhibitory factor (MIF) was inhibited by SMD, whereas mRNA for IL-10 was increased. SMD increased the IL-10 concentration in the peritoneal cavity and serum and decreased the concentration of IL-12 p40 in the serum, peritoneal cavity, and intracellularly in peritoneal cells (which are >80% macrophages). Similar effects on LPS-induced cytokine production were observed following dermal administration of SMD. The major breakdown product of SMD, methylisothiocyanate (MITC), caused similar effects on cytokine production at dosages as low as 17 mg/kg, a dosage relevant to human exposure levels associated with agricultural use of SMD. Treatment of mice with SMD decreased survival following challenge with non-pathogenic Escherichia coli within 24-48 h, demonstrating suppression of innate immunity.

Atmospheric emissions of methyl isothiocyanate and chloropicrin following soil fumigation and surface containment treatment in bare-root forest nurseries

Methylisothiocyanate (MITC) and chloropicrin (CP) are alternatives to methyl bromide for soil fumigation. However, surface transport of MITC emission has been cited as the cause for seedling damage in adjacent fields at several bare-root forest-tree nurseries. Field experiments were conducted at nurseries in Wisconsin and Georgia to measure air emissions of MITC and CP after fumigation. Four treatments were tested as combinations of two fumigants (dazomet or coapplication of CP and metam sodium) and two surface containment treatments (tarp or water seal). A very small percentage (<5%) of the applied equivalent of MITC was lost through either surface treatment over a 2-week period, and lower emissions occurred with the water seal. Cumulative emissions of CP accounted for 10%–22% of the applied CP. With all surface containment treatments, more than 70% of total cumulative emissions of either MITC or CP occurred within 1 week of application. Either surface containment treatment can be used by nursery managers to reduce risk of MITC emissions that could cause damage to nearby seedling crops or harm to humans.

Regulation of Microbial Organisms in Australia – A Technical Overview

The National Registration Authority for Agricultural and Veterinary Chemicals (NRA) is the regulatory body responsible for the coordinated registration, regulation and review of agricultural and veterinary (agvet) chemicals up to and including the point of retail sale. This role is defined by the Agvet Code, 1994. Each of Australia's eight states and territories retains its own jurisdictional controls over the use of agricultural and veterinary products. The NRA may issue permits to exercise control over research agricultural and veterinary (agvet) chemicals. Under defined emergency conditions, the NRA can also issue "emergency use" permits, and can approve the use of agvet chemicals for minor uses that do not normally appear on product labels, and would otherwise be illegal. The Existing Chemicals Review Program of the NRA reviews registered agvet chemical products to ensure that they meet contemporary standards for efficacy, safety and health, and pose no undue risk to the environment or trade. Recently reviewed chemicals include atrazine, metham sodium, endosulfan and ethylene dibromide, and certain changes to their registration and labelling are being implemented. Several other chemicals are currently under review. The Special Review Program allows the NRA to review registered agvet products if there are any special issues arising that may alter the terms of their original registration. Current challenges to the NRA include the management of insecticide and weed resistance, particularly in relation to the regulation of genes expressing insecticides and herbicide tolerance. Specific guidelines for the registration of microbiological products are currently being reviewed. Issues relating to the release of microbial organisms into existing agricultural Systems and environments require considered risk assessment prior to any approval. Macrobiological control agents are specifically excluded from regulation by the NRA. They may, however, be regulated under other pieces of legislation.

Evaluation of chemical strategies as alternatives to methyl bromide for the control of root-knot nematodes in greenhouse cultivated crops

If methyl bromide is phased out for greenhouse use by 1 January 2005 it will cause many difficulties in agricultural industries that are now heavily reliant on its use. Three field experiments were conducted to compare management tactics on tomato and cucumber in commercial greenhouses naturally infested with root-knot nematodes ( Meloidogyne spp.). Methyl bromide was used as a reference treatment and was consistently superior to all the other treatments and combinations of other fumigants with contact nematicides. A significant reduction of nematode juveniles and root-galling index was observed in plots treated with either metham sodium and cadusafos or 1,3-dichloropropene and cadusafos. Nematode decrease was greater when these three chemicals were applied in the same plots. Good nematode control based on the use of different chemicals combinations can be achieved only for one cropping season and therefore nematode management measures must be employed for the next cropping season

Methyl bromide alternatives for nematode and Cyperus control in bell pepper ( Capsicum annuum)

Three field trials were conducted to determine the efficacy of fumigant and herbicide combinations on nematode and Cyperus control in bell pepper ( Capsicum annuum L.). Various in-bed, broadcast and drip-applied fumigants were combined with napropamide, trifluralin, and a non-herbicide treated control. Results indicated that during all the three bell pepper seasons, metham sodium plus chloropicrin (MNa+Pic), and both the gas and emulsifiable formulations of 1,3-dichloropropene (1,3-D) plus Pic provided equal or better Meloidogyne control than methyl bromide (MBr) plus Pic. For Heterodera and Belonolaimus control, MNa+Pic and both formulations of 1,3-D+Pic were equally effective as MBr+Pic during the three bell pepper trials. For Cyperus control, the herbicides failed to improve weed control. For the fumigants, MBr+Pic consistently controlled the weed better than the others. However, most of the MBr alternatives reduced Cyperus populations with respect to the non-fumigant control. For bell pepper yield, the application of MNa and MNa+Pic provided similar fruit weight as for MBr+Pic in two of the three seasons.

First Report of Stunting and Root Rot of Potato Associated with Pratylenchus penetrans in the Columbia Basin of Washington.

The root-lesion nematode, Pratylenchus penetrans (de Man, 1880) Filipjev, 1936, is a common pathogen of potato in the United States east of the Rocky Mountains and frequently interacts with Verticillium dahliae to aggravate early dying disease (4). West of the Rocky Mountains, P. penetrans is associated with numerous crops including mint, tree, and small fruits but is rarely recovered from potato fields. Pratylenchus neglectus is a common plant-parasitic nematode on potato in the west, but causes little loss in yield and does not usually interact with V. dahliae (1). Management of P. neglectus is generally unnecessary; although a population of P. neglectus from Ontario, Canada appears to be more pathogenic and does interact with V. dahliae (1). During May 2003 (6 weeks after planting), large areas of stunted plants were observed in field inspections and in aerial photographs of two fields (50.6 ha) of cv. Ranger Russet in Benton County, Washington. Lower roots and stolons had numerous, dark lesions that are typical of P. penetrans damage and were severely stunted, while long, white roots had formed abnormally near the soil surface. In early May 2003, lesion nematodes (65 nematodes per 250 g of dry soil and 810 nematodes per g of fresh root weight) recovered from these potato fields were identified as P. penetrans on the basis of morphological characters (2,3). The crop responded to oxamyl (four applications at 1.1 kg of a.i. per ha between early May and mid-July), but the grower estimated that yields were 1.62 tons/ha (4 tons/acre) less than in comparable unaffected fields. To our knoweldge, this is the first report of severe damage to potato from P. penetrans in the Colombia Basin potato-production area. Soil fumigation with Telone II (1,3-dichloropropene) is commonly used in the Columbia Basin to control root-knot (Meloidogyne chitwoodi and M. hapla) and stubby-root (Paratrichodorus allius) nematodes, and metam sodium is used to control V. dahliae. However, since the only nematode recovered from preplant samples was assumed to be P. neglectus, and because cv. Ranger Russet is relatively tolerant to V. dahliae, no fumigant was used in these fields. An increase in mint production in this area may be responsible for introducing P. penetrans into previously uninfested fields since mint is propagated vegetatively and lesion nematodes are commonly associated with mint and could be easily spread in planting material and adhering soil. Identification of P. penetrans in stunted corn from two nearby fields during 2004 suggests that this nematode may be a new and emerging problem in this area. The Columbia Basin is one of the largest potato-producing regions in the United States, and widespread introduction of P. penetrans could add substantial cost to potato production in this area.

Peanut Response to Inoculation and Nitrogen Fertilizer

Experiments were conducted from 2000 through 2003 in North Carolina to compare peanut (Arachis hypogaea L.) response to inoculation with Bradyrhizobium In one study that included 20 experiments, peanut pod yield was compared following no inoculation or inoculation with commercial granular or liquid in‐furrow products. In six of these experiments, inoculant was also applied to the seed before planting. In six other experiments within this study, pod yield of inoculated and noninoculated peanut was determined following surface applications of N approximately 40 d after planting. In a second study, peanut pod yield was compared in twin row planting patterns (two rows spaced 18 cm apart on 91‐cm centers) when inoculant was applied in‐furrow to one of the twin rows or to both of the twin rows. In a third study, interactions of in‐furrow inoculation and fumigation with metam sodium were compared. Peanut pod yield was higher following inoculation in 7 of 20 experiments. In six of the seven experiments where a yield response to inoculation was observed, peanut had not been planted previously in these fields. In experiments where peanut responded positively to inoculant, pod yield was higher when inoculant was applied in the seed furrow rather than to seed before planting. Nitrogen increased pod yield linearly in three of six experiments (p ≤ 0.05). Inoculating both rows of peanut seeded in twin row patterns yielded higher in two of four experiments than when one of the twin rows was inoculated or when inoculant was not included. Fumigation with metam sodium did not affect pod yield, regardless of inoculation treatment.

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.

Agricultural Pesticide Use and Childhood Cancer in California

Household pesticide use has been associated with higher risk for several childhood malignancies, but few studies have evaluated risks associated with residential proximity to agricultural pesticide use. We conducted a population-based case-control study of early childhood cancer (age 0-4 years) among California children born between 1990 and 1997 and mother's residential proximity to agricultural applications of pesticides at the time of the child's birth. Included in the study were 2189 case children and 4335 controls matched for birth date and sex. We estimated the in utero exposure potential from specific chemicals and chemical groups used in the 9 months before birth within a half mile of the maternal residence. We computed odds ratios (ORs) using conditional logistic regression. No striking patterns emerged. There were modestly elevated ORs for leukemias associated with probable and possible carcinogen use, and with nearby agricultural applications of organochlorines and organophosphates during pregnancy. Two commonly used pesticides were associated with higher leukemia risk when comparing the highest and lowest categories: metam sodium (OR=2.05; 95% confidence interval=1.01-4.17) and dicofol (1.83; 1.05-3.22). The few elevated risk associations in this study are consistent with chance, given the large number of comparisons, but they may deserve more careful consideration. Future studies that integrate specific temporal and spatial exposure potential for targeted pesticides will be important in further evaluating risks associated with childhood cancer.

Drip Application of Alternative Fumigants to Methyl Bromide for Strawberry Production

Strawberry (Fragaria ×ananassa Duchesne) is a high-value cash crop that benefits from preplant soil fumigation with methyl bromide (MB) and chloropicrin (CP). Methyl bromide will be banned in the U.S. and other developed countries by 2005 for most uses. Potential alternative chemicals to replace methyl bromide for soil fumigation include CP, 1,3-dichloropropene (1,3-D), and methyl isothiocyanate (MITC) generators such as metam sodium (MS). Commercial formulations of these fumigants applied singly and in combination through drip irrigation systems were evaluated at two sites for three consecutive growing seasons as alternatives to MB:CP fumigation for strawberry production. A mixture of 1,3-D and CP was shank injected as Telone C35 (62% 1,3-D and 35% CP) at 374 kg·ha-1. An emulsifiable concentrate (EC) formulation of 1,3-D and CP was applied as InLine (60% 1,3-D and 32% CP) at 236 and 393 L·ha-1 through drip irrigation systems in three amounts of irrigation water (26, 43, and 61 L·m-2). Chloropicrin (CP EC, 96%) was drip applied singly at 130 or 200 L·ha-1. Metam sodium was applied singly as Vapam HL in three amounts of water and in combination with InLine and CP EC. Strawberry growth, fruit yields, disease pressure, and weed biomass were compared to an untreated control and shank injection with MB:CP mixture (67:33) at 425 kg·ha-1. For soils high in pathogen populations, fruit yield from the untreated plots was 34% to 50% relative to the MB:CP treatment. The greatest (95% to 110%) yields relative to MB:CP were in the high rates of the InLine treatments. Yields from simultaneous drip fumigation with a combination of Vapam HL and InLine or CP EC were less (67% to 79%) than yields from shank fumigation with MB:CP due to 1,3-D and CP hydrolysis reactions with Vapam HL or the generated MITC in the irrigation water that reduced the efficacy of these combinations to control soilborne pathogens. Application of reduced rates of InLine or CP EC followed 6 days later with reduced rates of Vapam HL controlled soil borne pathogens and weeds and produced the greatest fruit yield relative to all treatments. Chemical names used: 1,3-dichloropropene (1,3-D); methyl bromide (MB); trichloronitromethane (chloropicrin, CP); sodium methyldithiocarbamate (metam sodium); methyl isothiocyanate (MITC).

Incompatibility of metam sodium with halogenated fumigants

Metam sodium (metam) is a widely used soil fumigant. Combined application of metam and other available fumigants is intended to produce synergic pesticidal effects for a broad spectrum of pest control in soil fumigation. This study aimed to test the compatibility of metam with the halogenated fumigants 1,3-dichloropropene (1,3-D), chloropicrin, methyl bromide, methyl iodide and propargyl bromide. Halogenated fumigants and metam were spiked simultaneously into organic solvents, water and moist soils, and metam-induced degradation of these halogenated chemicals was evaluated. In all three media, the halogenated fumigants were incompatible with metam and degraded via rapid chemical reactions. The degradation rate varied with halogenated fumigant species and increased as the amount of metam present was increased. In moist soil, 15-95% of the halogenated fumigants were decomposed within 72 h by metam at a 1:1 molar ratio. Combined application of Telone C-35 (62.5% 1,3-D + 35% chloropicrin) at 265 mg kg(-1) and Vapam (42% metam) at 567 mg kg(-1) in soil resulted in complete disappearance of the applied chloropicrin and 20-38% of the 1,3-D within 8 h. The results suggest that simultaneous application of halogenated fumigants and metam at the same soil depth will not maximize pest control. In practice, sequential treatment of soil or application at different soil depths is recommended when these two types of fumigants are used in combination.

Chronic dietary risk for pesticide residues in food in Brazil: an update

The objective was to conduct a dietary risk assessment of pesticides registered in Brazil up to 14 January 2004. The theoretical maximum daily intake (TMDI) was calculated for 275 compounds using the Brazilian maximum residue limits (MRL) and food consumption. The chronic dietary risk assessment was conducted by comparing the TMDI with the Brazilian acceptable daily intake (ADI) or, when not available, with the ADI from other sources. The TMDI was higher than the ADI (%ADI>100) in at least one Brazilian region for eight pesticides, including five organophosphorus insecticides. For these compounds, the higher TMDI (expressed as %ADI) ranged from 140 (metam sodium) to 14 000 (methyl bromide). Rice, beans, citrus and tomato were the commodities that contributed most to ingestion. Change in pesticide use patterns and the establishment of ADIs by the Brazilian government have reduced the number of compounds for which the TMDI exceeded the ADI in the last 4 years. Risk assessment methodology based on TMDI calculation, however, is conservative as it assumes that the food supply is always treated with all the registered pesticides for that crop and that one always consumes food containing residues at the tolerance level. Furthermore, for six compounds with TMDI exceeding the ADI, a more realistic estimation of the pesticide daily intake was conducted using monitoring residue data from the Brazilian National Pesticide Residue Program. For these compounds, the higher refined intakes ranged from 2% (dimethoate) to 180% (fenitrothion) of the ADIs. The implementation of a national pesticide residue monitoring programme by the government was important to allow the refinement of the risk assessment. However, adequate daily food consumption data are still needed to assess better the public health risk to Brazilian consumers from food produced from crops treated with pesticides.

Effect of Combined Application of Methyl Isothiocyanate and Chloropicrin on Their Transformation

Combining several soil fumigants to increase the broad spectrum of pest control is a common fumigation practice in current production agriculture. In this study, we investigated the effect of combined application of chloropicrin and methyl isothiocyanate (MITC) on their transformations and persistence in the environment. In aqueous solution, no direct reaction between MITC and chloropicrin occurred and relatively slow rates of hydrolysis of these compounds were observed in aquatic environments free of suspended solids. The transformation of chloropicrin, however, was accelerated in aqueous solution with MITC because of a reduction reaction with bisulfide (HS(-)), which is a by-product of MITC hydrolysis. In soil, when fumigants were applied simultaneously, the degradation of MITC was suppressed under the bi-fumigant application due to the inhibition of soil microbial activity and a possible abiotic competition with chloropicrin for a limited number of reaction sites on the surface of soil particles. However, the degradation rate of chloropicrin was significantly enhanced in the bi-fumigant soil system, which was primarily attributed to the reaction of chloropicrin and HS(-). Two sequential application approaches were developed to investigate the feasibility of the combined application of metam sodium (parent compound of MITC) and chloropicrin in soil and assess their potential effects on environmental fate. For both application sequences, the degradation of chloropicrin was accelerated and that of MITC, as a major breakdown product of metam sodium, was inhibited in soil.

Efficacy of Mulches and Methyl Bromide Alternatives on Soilborne Pests and Weeds in Spring Tomato

Tomato (Lycopersicon esculentum Mill.) field studies were conducted to determine the impact of mulch types combined with soil fumigants on spring tomato yields and on soilborne pests and weeds. Fumigants were: a) untreated control, b) methyl bromide + chloropicrin (67/33%, respectively) at a rate of 400 kg haG , c) chloropicrin at 400 kg haG plus the herbicide pebulate at 4.5 kg haG , d) 1,3-dichlopropene 1 1 1 at 325 kg haG + chloropicrin at 67 kg haG (83/17%, respectively) plus pebulate at 4.5 kg haG and e) metam 1 1 1 sodium at 485 kg haG plus pebulate at 4.5 kg haG . Mulch types were either black low-density polyethylene film 1 1 (0.038 mm thick) or black paper mulch. Results indicated that all fumigants with either mulch type had higher tomato yield and more effective soilborne disease and purple nutsedge (Cyperus rotundus L.) control than the non-fumigated control. Paper mulch appeared to be a valuable alternative to control purple nutsedge with no fumigants and with low-volatility fumigants, such as metam sodium, whereas plastic mulch might retain high-volatility fumigants, such as methyl bromide, longer, thus increasing efficacy.

The effect of soil fumigants methyl bromide and metham sodium on the microbial degradation of the nematicide Cadusafos

Rapid biodegradation of Cadusafos in a soil from a previously treated greenhouse site from the area of Vasilika in Northern Greece was observed using both incubation and bioassay studies with nematodes. The slow rates of Cadusafos degradation observed in soils from the previously treated site after sterilization with chloroform and also in soils from an adjacent previously untreated site suggested that soil microorganisms adapted to metabolize Cadusafos were responsible for its rapid dissipation. Fumigation of the soil from the previously treated site with methyl bromide (MB) 9 months prior to the experimental addition of Cadusafos (4 μg g −1) only temporarily inhibited degradation of Cadusafos, unlike metham sodium (MS) whose application significantly hampered degradation of the nematicide. However, when the time interval between fumigation of soil from the previously treated greenhouse with MB and MS and the experimental application of Cadusafos was minimized to 20 d, both fumigants halted the rapid degradation of the nematicide. The transient inhibitory effect of MB on the microbial degradation of subsequent Cadusafos applications was attributed to the recovery of the soil microflora within 9 months. In contrast, the persistent inhibitory effect of MS on the microbial degradation of Cadusafos might have been caused by the adverse effects of the fumigant on the microorganisms, which were responsible for the rapid degradation of Cadusafos in the specific soil, although this was not tested in this study. According to these findings, the combined application of MS as a pre-planting treatment with a post-planting application of Cadusafos would maximize the biological efficacy of the non-fumigant nematicide by extending its persistence and preventing the development of enhanced biodegradation for organophosphorus nematicides such Cadusafos.

Sanitation practices that inhibit reproduction of Monosporascus cannonballus in melon roots left in the field after crop termination

Ascospores of Monosporascus cannonballus function as primary inoculum for infection of melon roots. Previous studies demonstrated that pathogen reproduction (i.e. ascospore production) occurs on infected melon roots primarily after the crop has been terminated. Therefore, the key to maintaining low soil population densities of the pathogen is to destroy the hyphae of the pathogen in infected roots as soon as possible after crop termination, thereby inhibiting ascospore production. Results from a 3‐year field study demonstrated that, relative to the nontreated controls, an immediate postharvest application of metam sodium (applied via the drip irrigation system at 187 L ha−1) or cultivation (which lifts roots onto the surface of the soil for rapid desiccation) significantly inhibited pathogen reproduction in infected melon roots, as shown by the number of roots subsequently bearing perithecia. Additionally, ascospore populations in plots that received either the metam sodium or cultivation treatment were significantly lower (P < 0·05) than populations in the nontreated control plots at the end of the 3‐year study. These results demonstrated the efficacy of these postharvest treatments in the inhibition of pathogen reproduction and retardation of inoculum build‐up in soil.