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The induction of Fusarium wilt by continuous cropping has become a severe problem for watermelon cultivation around the world. Here, the feasibility and underlying mechanism of soil fumigation with ammonium bicarbonate (AB) or metam sodium (MS) under high temperature (HT) were investigated for the control of Fusarium wilt during watermelon growth on continuously cropped soils. Both AB + HT and MS + HT decreased the density of Fusarium oxysporum f. sp. niveum (FON) in soil, improved the soil properties (i.e. increased the pH, reduced salinity, improved soil nutrients, balanced soil micro-ecology, and increased soil enzyme activities), and consequently decreased the Fusarium wilt incidence and improved the watermelon fruit quality. In vitro, MS treatment stopped the growth of FON on medium, while AB mixed with lime (but not AB) alone inhibited FON growth. AB or MS fumigated soils under HT also decreased Fusarium wilt incidence of watermelon seedlings after artificial FON infection. Consequently, AB + HT and MS + HT can control continuous cropping-induced Fusarium wilt by both inhibiting FON growth and improving the soil environment.

A decline in red raspberry (Rubus idaeus) crop longevity has been partially attributed to parasitism by the plant-parasitic nematode Pratylenchus penetrans. Soil fumigation with 1,3-dichloropropene (1,3-D) and chloropicrin is the most common management practice for P. penetrans in this production system, but the effects are variable and there are strict regulations regarding application; alternatives are needed. A three-year study was conducted in a replanted commercial red raspberry field with a history of P. penetrans to evaluate brassicaceous seed meal (BSM) soil amendment combined with root inoculum removal (RR) as preplant alternatives to traditional soil fumigation with 1,3-D and chloropicrin. Additionally, the fumigant metam sodium at full and half rates with root removal was evaluated. Treatments were applied once prior to planting and included: BSM at 3.4 t ha−1 with RR, full rate metam sodium (692 L ha−1; Max Fum) with RR, half rate metam sodium with RR (Min Fum), and full rate metam sodium without RR (Max Fum–RR; control). Data collected included: P. penetrans population dynamics in soil and raspberry roots, microbial (bacterial and fungal) communities in soil, raspberry vegetative growth, estimated yield, and fruit total soluble solids (TSS) concentration. Population densities of P. penetrans in soil and roots were significantly higher in BSM (983–4801 P. penetrans g−1 of root) than in Max Fum and Max Fum–RR (32–802 and 40–1509 P. penetrans g−1 of root, respectively) during the first two years of the study. By the end of the study there were no differences in P. penetrans population densities among the treatments. Root removal did not affect P. penetrans densities as there were no significant differences between Max Fum and Max Fum–RR. Min Fum was more effective than BSM at reducing P. penetrans population densities, but not as effective as Max Fum or Max Fum-RR. The only difference among treatments regarding the soil microbial community was observed in the first spring after treatment application, when BSM had a soil bacterial community that differed from the other treatments; this difference did not persist into the next sampling date. The most noticeable differences in bacterial and fungal soil communities were due to season, not treatment. There were no significant differences in raspberry vegetative growth the first summer after planting. Yield or TSS did not differ in the second and third summer after planting. The current data show that Min Fum, BSM amended to soil at this experimental rate, and root removal are not effective in reducing P. penetrans population densities, but yield and fruit quality are not compromised under the conditions of the experiment.

Dimethyl disulfide (DMDS) is a methyl bromide alternative with good to excellent nutsedge control when mixed with chloropicrin (Pic). Combining fumigants is a common practice to improve pest control spectrum, however, the use of Pic is restricted in some countries. In order to determine the legitimacy of replacing Pic in DMDS:Pic combinations, a low and high rate of metam sodium (MNa) was used alone and in combination with DMDS and were compared to a single rate of DMDS alone and in combination with Pic to determine their efficacy against nutsedge species and impact on muskmelon yield. All DMDS combinations resulted in lesser nutsedge populations than MNa alone and the non-treated control. MNa applied alone, even under totally impermeable film, was not enough to control nutsedge species. DMDS combinations also provided greater nutsedge control than DMDS applied alone at seasons end. Furthermore, MNa applied concurrently with DMDS may have the potential to replace DMDS:Pic combinations without losing efficacy on nutsedge species in geographies where the use of Pic is restricted.

Metam sodium is a fumigant used as a crop pretreatment in agriculture to control a wide array of pests, and soil borne diseases that may adversely affect plant quantity and quality. This present study utilized control and treated field plots to examine the effects of metam sodium on indigenous soil microbes in terms of numbers, activity, and diversity. Following metam sodium application, culturable heterotrophic counts in all soils increased significantly for 24 h, but quickly returned back to original levels. Application resulted in decreased microbial activity, detected by ATP-based assays, that was significantly lower in treated soils than control plots, but recovered quickly. High-throughput sequencing of the 16S rRNA gene showed that treated plots contained significantly lower numbers of observed OTUs, particularly 14, 21, and 28 days after treatment. Soil bacterial communities were significantly altered by MS-treatment due to increased relative abundances of Actinomycetales, Bacilli, and Chloroflexi, as well as decreased Acidobacteria. These dominant taxa observed in MS-treated plots are major contributors to biological activity in various healthy soils and rhizospheres. Therefore, the increase in relative abundance of these biologically productive phyla coupled with abundant ATP production suggests that soil health recovered following MS-treatment and remained functionally intact.

Chemical fumigation and biofumigation are used to reduce soil-borne diseases in agricultural production systems; however, other essential soil processes such as the soil nitrogen (N) cycle may also be affected. This study compared the effects of chemical fumigation and biofumigation on soil net N mineralization, nitrification, denitrification, and soil nitrifier and denitrifier abundance. Six treatments were compared using soil microcosms over a 160-day incubation period: fumigation with chloropicrin; fumigation with metam sodium used alone (MS) or combined with barley plant residues (MSBR); biofumigation with mustard residues; addition of non-biofumigant barley residues; and an untreated control. Biofumigation did not inhibit soil nitrification, whereas chemical fumigation with MS (with or without barley) and chloropicrin inhibited nitrification for 16 and 64 days, respectively. Biofumigation, barley residues, and MSBR increased soil respiration, N2O emission, and denitrification rates. However, biofumigation had lower denitrification and N2O cumulative emissions and rates compared to barley residues, suggesting that biofumigation may reduce N2O production pathways. All chemical fumigation treatments significantly decreased nitrifier gene abundance compared to biofumigation; however, only chloropicrin decreased the abundance of denitrifying genes. After 160 days, 22% of the added plant residue dry matter remained in the MSBR-treated soil, which was ∼2-fold greater than the barley-treated soil, indicating chemical fumigation may also affect the carbon cycle. Overall, these results suggest that chemical fumigation, especially with chloropicrin, has a greater impact on nitrification and nitrifier and denitrifier gene abundance than biofumigation with mustard residues.

Soil solarization is a non-chemical soil disinfestation method proven effective against soil-borne pathogens and weeds. However, it should be assessed under local cropping conditions before it can be implemented in commercial crops, since the process is highly dependent on climate conditions, among other factors. Soil biosolarization combines biofumigation with solarization to improve its effectiveness but knowledge about its use on tomato crops is still rather scarce and limited to nematode control. We have tested the effectiveness of soil solarization, biosolarization and fumigation with metam sodium over three tomato cropping seasons, to control corky root caused by Pyrenochaeta lycopersici and weeds under screen-house conditions in the Canary Islands (Spain). During the three seasons, maximum soil temperatures at 10 cm depth in solarized and biosolarized plots were about 10 °C higher than in controls, rising up to 41.4–43.3 °C in solarization and 43.0–44.7 °C in biosolarization, with an accumulated number of hours exceeding 40 °C of 48.8–138.2 and 92.3–204.7 h in solarized and biosolarized plots, respectively. The most effective treatment was biosolarization, which significantly increased tomato yield by 12.4% in 2001–02; 22.8% in 2002–03 and 22.2% in 2003–04, and reduced corky root severity in the last two seasons. Corky root was also significantly reduced by solarization in 2003–04, whereas there was no difference between metam sodium and control plots in any season. Weed infestation was evaluated in 2002–03 and 2003–04, in which weed density in biosolarized plots was significantly lower than in controls (88.8% and 50.6% reduction at 45 and 165 days after tomato transplanting in 2002–03; and 69.6% after 120 days in 2003–04). In contrast, weeds were not controlled by solarization, and inconsistent results were obtained with metam sodium. Here we show that soil biosolarization is clearly a way to improve the effectiveness of soil solarization under less favorable environmental conditions, like those prevailing in tomato screen-houses in the Canaries, and a feasible alternative to chemical fumigation for the control of corky root and weeds.

Fusarium wilt, caused by Fusarium oxysporum f. sp. spinaciae, is a significant constraint to the summer production of bunching spinach in Ontario, Canada. Trials were conducted to assess soil amendments (limestone) and fumigants (metam sodium, chloropicrin and dazomet) for the suppression of Fusarium oxysporum f. sp. spinaciae. Dolomitic limestone applied at a rate of 10 and 20 t ha−1 reduced the incidence of fusarium wilt by 10 and 47%, respectively, even though there was little change in soil pH (7.4–7.5) or soil calcium concentration (1598 vs 1483 in 20 t lime vs control, respectively. Fusarium wilt severity was lower in the 2013 than in the 2014 growing season. In 2014, the fumigants metam sodium, chloropicrin and dazomet reduced the population of Fusarium spp. propagules in the soil by 84, 93 and 100%, respectively. Chloropicrin provided the best control of the spinach fusarium wilt pathogen compared to the other fumigants but was only assessed one year. Chloropicrin was the only treatment to truly reduced spinach Fusarium wilt by preventing vascular discolouration. Brassica juncea and calcium cyanamide were not effective at suppressing the disease. A high rate of nitrogen, consisting of polymer coated sulphur coated urea, was applied to provide the same rate of nitrogen as the Brassica juncea and calcium cyanamide treatments. Applying nitrogen in this formulation was as effective as metam sodium in reducing the incidence and severity of Fusarium wilt and should be evaluated further to determine the economics and environmental impact of this approach.

Preplant soil fumigation is commonly used to control soilborne pathogens and weeds in forest seedling nurseries of Oregon and Washington. However, lower chemical inputs are desired to meet state and federal application regulations, to minimize buffer zone size requirements, and to help protect the environment. Therefore, the objectives of this research were to evaluate the efficacy of three reduced rate soil fumigants under totally impermeable film (TIF) in managing soilborne diseases and weeds, and to determine if combined applications of up to four biocontrol agents improved soilborne disease control. Reduced rates of methyl bromide, metam sodium, and 1,3-dichloropropene, all applied in combination with chloropicrin, were effective in decreasing soil populations of Pythium and Fusarium as well as the presence of Pythium in root debris from the previous crop. The roots of Douglas-fir (Pseudotsuga menziesii) seedlings transplanted into each fumigant treatment were also colonized less by Pythium and Fusarium than those transplanted into nonfumigated control plots. However, biocontrol treatments were not effective against either pathogen. Weed biomass and weeding times were also significantly reduced by fumigation. Application costs were similar for all three fumigant treatments, but seedling size was largest from the methyl bromide and metam sodium treatments followed by the 1,3-dichloropropene treatment. Based on the results of this study, reduced rates of methyl bromide, metam sodium, and 1,3-dichloropropene show promise in managing soilborne diseases and weeds in forest nurseries.

Two strawberry nursery field trials comparing soil disinfection with different fumigants (metam sodium, dazomet, chloropicrin, chloropicrin +1,3D) and a steaming system exploiting the exothermic reaction between steam and CaO (Bioflash System™) were conducted in 2010–2012 to evaluate the effect of treatments on Verticillium dahliae Kleb. inhabiting the soil, and on plant health, growth and yield of strawberry daughter plants. Chemical fumigants and the Bioflash System™ decreased the number of V. dahliae colonies in the soil, which corresponded to reduced incidence of Verticillium wilt (efficacy about 80%). The use of chemical fumigants had a positive impact on the size of the mother plants. The surface area covered by plants grown on the treated plots was 1.1–1.7 times larger than plants grown on non-fumigated control plots. The number of runners, as well as daughter plants, produced from plants grown on plots treated with all chemical fumigants was significantly higher than in the non-fumigated control or in the plots treated with the Bioflash System™. The disinfection treatments significantly increased the yield of marketable daughter plants, approximately 1.5–3 times higher in comparison to plants grown on control plots. Steam disinfection with the Bioflash System™ was the least effective treatment in this respect. The differences in marketable plants yield among the chemical fumigants significantly affected the net marginal return and the return on investment of the crop. In this respect, the steam disinfection was economically efficient only in one season. The efficacy in controlling Verticillium wilt even with low doses of metam sodium and dazomet and their influence on yield and quality of daughter plants is confirming the feasibility of these fumigants for strawberry nursery management.

There is an urgent need to test and develop sustainable methods for management of soil pathogens, such as the root-lesion nematode Pratylenchus penetrans and the soil fungus Verticillium dahliae. Ultimately this should be investigated with a multidisciplinary approach, with long-term measurements of biological and chemical parameters and their final impact on crop yield under field conditions. The present study focusses on eight soil health treatments (compost, chitin, marigold, grass–clover, biofumigation, anearobic soil disinfestation, a physical control method and a combination of marigold, compost and chitin) and two control treatments (a chemical control with 300 L/ha Metam sodium and un untreated control). These 10 treatments were studied for their effects on soil chemical quality, soil pathogens and their impact on the yield of potato, lily and carrots during 6 years. The present study did demonstrate that in comparison to chemical control, additions of chitin, anaerobic soil disinfestation and marigold are already excellent alternatives for the control of plant-parasitic nematodes and V. dahliae. We also demonstrated that grass–clover, biofumigation, Cultivit and compost are not effective alternatives for chemical control yet and further development is needed. All treatments caused a yield increase in comparison with the control. The biggest increases of more than 60% were found for the treatments with chitin. Furthermore it was demonstrated that these yield increases were probably less influenced by changes in chemical soil properties, but the consequence of changes in the soil biota, in this case especially the effective control of P. penetrans and V. dahliae. Furthermore it has been demonstrated that most of these soil health treatments could already be implemented in an arable crop rotation and probably adapted for many areas of the world where other alternatives, such as solarisation or soil flooding, are not feasible or too risky.

Isothiocyanates (ITCs), a series of new nematicides of the –N C S group, were evaluated for their efficacy against root-knot nematode Meloidogyne javanica. Of the compounds tested, AllylITC, AcITC, EtITC, BzTC, BzITC, 1-PEITC and 2-PEITC showed in vitro irreversible nematicidal activity against second-stage juveniles of M. javanica, following exposure for 72 h at concentrations as low as 5 μg mL−1. When exposed to AllylITC, AcITC and EtITC at lower concentrations, motile juveniles also became irreversibly immobile in 3 days, with a LC50 value at 2.76, 2.53 and 3.05 μg mL−1, respectively. In the pot experiments, 1.0 ml AllylITC and 1.1 ml AcITC per kg of soil controlled M. javanica, similarly to or better than metam sodium at its recommended dose. Similar results were obtained in the field experiments using 1.0 kg AllylITC or 1.0 kg AcITC ha−1. Based on the results of this study, AllylITC and AcITC have potential to be used as new bio-fumigant nematicides.

SUMMARY The use of built-up litter is currently standard practice in the US poultry industry. However, there is the potential for pathogens to accumulate in built-up litter. One significant pathogen associated with a variety of diseases in poultry is Clostridium perfringens. This particular bacterium is relatively hardy and can survive even some of the more rigorous litter treatments commonly used by the poultry industry. It was the purpose of this research to determine the efficacy of a common soil fumigant, metam-sodium, in reducing C. perfringens numbers in the litter. In addition to C. perfringens, total aerobic and anaerobic bacterial numbers were measured after the product was applied at 1, 3, and 5 gal/ton (4.17, 12.52, and 20.86 mL/kg). This product had only a minor effect in reducing C. perfringens numbers. Conversely, aerobic bacteria were significantly reduced at all application levels, and anaerobic bacteria were significantly reduced at levels of 3 and 5 gal/ton. Because of the inability of this product to influence ammonia, pH, or litter moisture levels, we concluded that it is best used in conjunction with one of the currently available litter treatments for reducing overall bacterial numbers.

Two field studies were conducted to determine the effect of diverse soil fumigant and herbicide combinations on Meloidogyne root galling, Cyperus populations, and tomato growth and yields. Treatments consisted of combinations of the herbicides napropamide plus trifluralin, the soil fumigants 1,3-dichloropropene plus chloropicrin (1,3-D+Pic), Pic, and metam sodium (MNa), and doses of the nematicide fosthiazate. A non-treated control was also included. The fumigation programs that included the herbicides napropamide+trifluralin in pre-emergence and post-directed trifloxysulfuron in combination with either Pic and fosthiazate or 1,3-D+Pic and MNa proved to be effective means to suppress root galling and Cyperus interference while maintaining high tomato marketable yields.

Concentrations in soil and efficacy of 1,3-dichloropropene (1,3-D)+chloropicrin and methyl isothiocyanate (MITC) against the survival of Phytophthora capcisi, Rhizoctonia solani and yellow nutsedge (Cyperus esculentus L.) were studied in plastic-mulched Southern Georgia sandy soil beds. Beds were treated with InLine (60.8% 1,3-D+33.3% chloropicrin) at 93.5, 187, and 280.5 l ha−1 and Vapam (42% metam sodium) 233.8, 467.5 and 701.3 l ha−1. 1,3-D+chloropicrin and MITC concentrations in soil were monitored after drip application for 7 d and 240 h, respectively, from pre-selected sites in beds. 1,3-D+chloropicrin and MITC concentrations decreased with time and distance from the emitter. Survival of P. capsici, R. solani and yellow nutsedge in treated beds was higher with distance from the emitter. These methyl bromide alternatives did not diffuse laterally at effective concentrations beyond the point of application. Improved application techniques are required to improve the lateral distribution of these alternatives.

Multiple Brassica species commonly grown in Georgia were evaluated as a potential alternative to methyl bromide for management of root-knot nematode in vegetables. Brassica species produce general biocides called glucosinolates and were grown as cover crops and incorporated as green manures prior to transplanting of vegetable crop. Nematicidal activity of the Brassica species was based on net changes in nematode population and root damage caused by root-knot infection and feeding. Plant growth and crop yield was also evaluated to determine the response of the subsequent vegetable crop to the incorporated Brassica species. Incorporation of select Brassica species reduced root-knot populations and root damage caused by root-knot infection comparable to non- Brassica species cover crops with metam sodium in most years; however, the level and consistency of the nematicidal activity varied between and within Brassica species. Variations in plant growth and yield were also observed among and with Brassica and non- Brassica species. Generally, increased growth and yield corresponded with cover crop treatments that had the lowest levels of root-knot nematode populations at planting of the subsequent crop. Several cover crop treatments had a negative affect on the growth and yield potential of the vegetable crops. Therefore, a producer will need to choose a Brassica species cover crop that can significantly reduce nematode populations without adversely affecting the growth/yield of the subsequent vegetable crop.

Henry's Law coefficients were measured for the first time for chloropicrin and methyl isothiocyanate (MITC) at 25 °C in deionized water, in 0.10 M NaCl, in 0.20 M NaCl, and in pH 4.0 and 8.0 buffered solutions. For chloropicrin, the Henry's Law coefficient was 2.1±0.3 atm M−1, and did not show significant pH dependence or dependence on ionic strength. For MITC, the coefficient was much smaller, 0.06±0.05 atm M−1. The Henry's Law coefficient for MITC did show dependence on ionic strength, increasing to 0.14±0.05 atm M−1 at 0.20 M, but did not appear to depend on pH. MITC has a much stronger tendency to remain in solution than chloropicrin. The transport of chloropicrin from solution to the atmosphere is likely to be significant environmentally, while MITC shows a much lower rate of volatilization. When transferred to the atmosphere, oxidation and photochemical reactions are likely to dominate the transformation of both chloropicrin and MITC, rather than heterogenous reactions.

The impacts of the 30 active substances, most used in Costa Rica (reference year 1998), are evaluated using two models originally developed to support comparative assertions in the context of the life cycle assessment: the multimedia fate, exposure and effect model Impact Assessment of Chemical Toxics 2002 (IMPACT 2002), and the Dynamic Model for Pesticides Residues in Plants. Results show that only five active substances - namely diazinon, mancozeb, chlorothalonil, terbutylazine and ethoprophos - contribute to more than 75% of the aquatic ecotoxicity and yet represent less than 40% of the amount used. More than 90% of the human toxicity is generated by only two active substances - namely terbufos and chlorothalonil - whereas they represent less than 10% of the total amount used. Overall, it would be possible to achieve a 90% reduction of human toxicity and a 75% reduction of aquatic ecotoxicity due to pesticide used in Costa Rica, focusing on only a few active substances. For instance, propiconazole or tridemorph could potentially be replaced by chlorothalonil; ametryn, diuron or paraquat by glyphosate; terbufos by cypermethrin; methyl bromide by metam sodium. (c) 2006 Elsevier B.V. All rights reserved.

Metam sodium is the most widely used soil fumigant in the United States. The primary breakdown product of metam sodium in soil is methyl isothiocyanate (MITC), an active pesticidal agent with a high toxicity and a great potential for volatilization. Reducing atmospheric emissions of MITC is therefore critical to maintain air quality. The objective of this study was to examine the rate and efficiency of conversion of metam sodium to MITC in soil and to investigate the potential of using surface water sealing to reduce MITC emissions. The conversion of metam sodium to MITC was a rapid abiotic decomposition process. At typical field application rates, the conversion efficiency depended on the initial content of metam sodium in soil, but was independent of soil moisture, soil type, and soil atmospheric conditions. A soil column system was used to measure the emission and distribution of MITC after subsurface and surface application of metam sodium. Volatilization flux and cumulative emission loss of MITC was substantially reduced with surface water sealing compared to uncovered soil columns after subsurface application of metam sodium. When metam sodium was surface applied in simulated chemigation, surface water sealing was ineffective, suggesting the need for additional emissions reduction practices when metam sodium is broadcast. Overall, the results of the column experiment indicate that surface water sealing with subsurface application of metam sodium may be an effective and economical strategy to reduce MITC emissions while maintaining pest control efficacy.

Three field trials were conducted with alternatives to methyl bromide (MBr) fumigation programs to control soilborne diseases, nematodes, and weeds in fresh market tomato (Lycopersicon esculentum Mill.). Treatments compared combinations of promising MBr alternatives, such as 1,3-dichloropropene+chloropicrin (1,3-D+Pic) applied with various herbicides, and virtually impermeable film (VIF); Pic in combination with metam sodium (MNa) or pebulate and fosthiazate; propylene oxide; and sodium azide. There was a non-treated control in each season. In all three planting seasons, the fumigation programs composed of: (a) 1,3-D+Pic with either napropamide+halosulfuron, metolachlor, or trifloxysulfuron, (b) Pic followed by MNa, and (c) Pic, fosthiazate and pebulate were as effective as MBr+Pic. During two of the seasons, 1,3-D+Pic with VIF, sodium azide at 85 kg/ha, and propylene oxide were consistently equal to MBr+Pic.

Two field trials were conducted to examine the efficacy of methyl bromide (MBr) alternatives in the control of Cyperus rotundus L. (purple nutsedge) and Fusarium oxysporum Schlecht. f.sp. lycopersici (Sacc.) Snyder & Hansen (Fusarium wilt) in fresh market tomato ( Lycopersicon esculentum Mill.). Various treatments compared combinations of soil fumigants and herbicides based on methyl bromide, chloropicrin, 1,3-dichloropropene, metam sodium, dazomet, and pebulate. The data show that consistently 1,3-dichloropropene plus chloropicrin at both doses in combination with the herbicide pebulate can be considered alternatives to methyl bromide in fresh market tomato. These treatments had excellent purple nutsedge and Fusarium wilt control, and marketable tomato yields were similar to that for methyl bromide plus chloropicrin.

Field trials were conducted in tomato ( Lycopersicon esculentum Mill.) to determine the efficacy of combinations of fungicides, nematicides, and herbicides on soilborne pest and Cyperus rotundus L., in comparison with methyl bromide+chloropicrin (MBr+Pic). Fumigants were: (a) MBr+Pic (98:2, respectively) at a rate of 450 kg/ha, (b) Pic at 225 kg/ha, (c) metam sodium (MNa) at 945 l/ha, (d) dazomet at 400 kg/ha, (e) dazomet at 510 kg/ha, (f) 1,3-D+Pic (C-17, at 83:17, respectively)+pebulate at rates of 200 l/ha and 4.5 kg/ha, respectively, (g) C-17+pebulate at 330 l/ha and 4.5 kg/ha, respectively, and (h) fosthiazate+MNa+pebulate at rates of 4.2 kg/ha, 945 l/ha, and 4.5 kg/ha, respectively. The results indicate that season-long control of purple nutsedge could be consistently achieved with C-17+pebulate at either dose, or fosthiazate+MNa+pebulate, in addition to MBr+Pic. Nematode root galling was steadily reduced by dazomet at a rate of 510 kg/ha, C-17+pebulate at either rate, or fosthiazate+MNa+pebulate. All these treatments provided the same nematode control than MBr+Pic. Only C-17+pebulate at either 330 l+4.5 kg/ha or 200 l+4.5 kg/ha was consistently equal to MBr+Pic on tomato fruit weight.

The behavior of methyl isothiocyanate (MITC), active metabolite of metam-sodium (MS), was studied under field conditions in Morocco. MS was applied through drip irrigation in: (i) uncovered soil, (ii) soil covered with transparent polyethylene, and (iii) soil covered with virtual impermeable film. Concentrations of MITC were determined at different soil depths to determine the distribution of MITC and the concentration-time product (CTP). Six hours after MS application, in a sandy soil, MITC reaches the 20-30 cm soil layer, but remains highly concentrated in the upper 10-20 cm soil layer. In a silty clay soil, MITC was concentrated in the upper 0-10 cm soil layer. The dissipation of MITC under different conditions of application was fast and complete after seven days. However, MITC dissipation time (DT 50 ) was

Metam-sodium (MS) and dazomet (DAZ) are soil fumigants that generate methyl-isothiocyanate (MITC) in soil. The latter effectively controls soilborne plant pathogens. Recently, we have found that repeated applications of MS yield less effective pathogen control. Soil samples collected from 12 field sites in Israel without (nonhistory) or with (history) previous applications of MS or DAZ were tested for MITC generation and dissipation. Accelerated MITC degradation in history soils, as reflected by a sharp reduction in the concentration×time (C×T) values and half-lives of MITC, was evident in most of the tested history soils. Exposure to MS and DAZ in those soils resulted in a significant reduction in Verticillium dahliae, Sclerotium rolfsii and Fusarium oxysporum f. sp. radicis-lycopersici mortality compared to exposure in nonhistory soils. The chemical and biological assays were well correlated. This is the first report of accelerated degradation of MITC resulting from repeated applications of DAZ. MITC was rapidly degraded in soils which had been previously treated with either MS or DAZ, indicating induced cross-accelerated degradation with both fumigants. In two field soils, accelerated degradation of MITC capacity was still evident for 18 to 30 months after treatment. This study suggests that accelerated degradation of MITC is a likely cause of the poor pathogen control observed in commercial potato and peanut fields upon repeated application of the fumigants MS and DAZ, and emphasizes the need for rational use of pesticides to maintain their efficacy.

Chloropicrin is a potential replacement for methyl bromide as a preplant soil fumigant. Its weed control efficacy was evaluated in a laboratory dose–response study and in a commercial strawberry field. Laboratory studies found that an increase in chloropicrin concentration and exposure time reduced the percentage of viable Stellaria media (L.) Mill., Portulaca oleracea L. and Polygonum aviculare L. seed. Chloropicrin applied to the field at 83, 110, 138, 165 and 220 kg/ha reduced the percentage of viable P. aviculare , P. oleracea and S. media seed. The seed of Malva parviflora L. and Erodium cicutarium (L.) L’Her was not affected. Metam sodium applied at 468 l/ha after chloropicrin improved weed control compared to chloropicrin alone. Standard polyethylene or virtually impermeable tarpaulin was used to cover beds after fumigation. The type of tarpaulin resulted in only a small reduction in the percentage of viable M. parviflora seed.

Metam sodium alone and in combination with 1,3-dichloropropene plus 17% chloropicrin (1,3-D+C-17) were evaluated under polyethylene mulch film as alternatives for methyl bromide in tobacco and tomato transplant production for both efficacy against pests and crop safety. Eight different weed species, 10 genera or species of fungi and several agronomic criteria were evaluated at three different sites. In general both the metam sodium alone and in combination with 1,3-D+C-17 were highly efficacious when compared to methyl bromide. Short polyethylene film retention times and short aeration times resulted in poor stands and poor crop vigor while relatively long polyethylene film retention times and long aeration periods at the same rates typically resulted in high stand counts and vigor. Combination treatments were more phytotoxic to germinating seed of tobacco and tomato. Vigor and stand counts of the seedlings were higher as aeration time increased, suggesting phytotoxic residues dissipate with time. Method of application of metam sodium, either injected with chisels or sprayed onto the soil surface and incorporated with a tractor-powered tiller alone or co- applied with 1,3-D+C-17 chisel injected, did not affect the efficacy of the treatments. Caution regarding phytotoxicity must be exercised when seeding into soil fumigated with metam sodium alone or combined with 1,3-D+C-17. Additional work will be required to establish safety periods required prior to transplanting crops into fumigated soil.

Golf course putting greens in the United States are normally built with a root-zone mix composed of >80% sand and a peat source. Populations of seven aerobic bacterial groups, commonly associated with soil or plant roots, were monitored during the building, planting and establishment of miniature bermudagrass putting greens, with a different set of greens built in each of 2 years. At each phase of construction, including pre- and post-fumigation, the following bacterial groups were enumerated: fluorescent pseudomonads, Gram-positives, Gram-negatives, Stenotrophomonas maltophilia , actinomycetes, heat-tolerant and total aerobic. The fumigants methyl bromide, dazomet and metam sodium were used at either normal or 10× field rates. In both years, by 50–70 days after fumigation, which included 4 weeks after planting, the size of the populations for all of the bacterial groups were either greater than or similar to the size of the populations prior to fumigation. The sand source, peat source, and fumigant source and amount did not have any long-term detrimental effects on size of the populations of any of the bacterial groups evaluated.

Metam-sodium, chloropicrin, 1,3-dichloropropene (1,3-D), 1,3-dichloropropene plus 17% chloropicrin (1,3-D+C-17) and 1,3-dichloropropene plus 35% chloropicrin (1,3-D+C-35) were evaluated alone and together under a polyethylene cover as alternatives for methyl bromide in tobacco, tomato and pepper transplant production over a two-year period. Eleven different weed species, 10 genera or species of fungi, two arthropods and four species of nematodes were evaluated in three different sites. All of the fumigant candidates were successful in controlling some of the pests. However, metam-sodium alone and in combination with 1,3-D+C-17, chloropicrin, and 1,3-D+C-35 were the most efficacious. Seventy-nine different parameters were measured over the two-year period including plant stands, vigour, plant heights and control of weeds, fungi, arthropods and nematodes. Metam-sodium and methyl bromide plus 2% chloropicrin (MeBrC) were not significantly different ( P =0.05) from each other in 76 of the 79 parameters evaluated; MeBrC was significantly better than metam-sodium for three of the 79 parameters. The combination of metam-sodium plus 1,3-D+C-17 was not significantly different from MeBrC for 74 of the 79 parameters tested. MeBrC was more efficacious than metam-sodium plus 1,3-D+C-17, for two of the 79 parameters, and metam-sodium plus 1,3-D+C-17 was significantly better than MeBrC for three of 79 parameters.

Rose plants grown in untreated used tuff are less productive than those grown in new, unused tuff. The objectives of the present work were to evaluate the effect of disinfestation of used tuff on the productivity of roses and to determine the effects of disinfestation treatments on the chemical properties of tuff. Rose ( Rosa × hybrida cv. `Mercedes') plants were grown in tuff media: unused; used, in which roses had been grown for 8 years, without disinfestation; or used, following one of three disinfestation methods: fumigation with 0.5% metham-sodium, solarization; or solarization+fumigation with 0.3% metham-sodium. Rose plants grown in untreated used tuff had lower yield than those grown in unused tuff. Solarized or fumigated tuff produced yields which were similar to those of unused tuff, while the combination of the two treatments resulted in yields which were superior to those of either unused or single disinfested used tuff. Flower quality was not affected by any of the treatments. Soluble organic matter (SOM) and N–NO 3 ions do not exist in unused tuff and gradually accumulate in used tuff. SOM affects nutrients availability, specially phosphorus through their effect on surface charge density and by preventing the precipitation of insoluble of Ca–P and Al–P compounds. This positive effect can be translated to higher yield only after used tuff is disinfested. Disinfestation further increased the content of SOM and of N–NO 3 thus additionally increasing nutrient availability.

Tobacco and pepper are high-value cash crops in the southeastern USA that require vigorous transplants free of pathogens and insects. Typically soil seedbeds are treated with methyl bromide prior to seeding. Soil fumigants metam-sodium, dichloropropene, chloropicrin and dazomet covered with polyethylene film were evaluated at several rates alone and in combination as alternatives for methyl bromide soil fumigation of tobacco and pepper seedbeds. The studies were conducted over a three-year period, with materials applied in the fall prior to seeding at the beginning of the following year. Nematode and insect pressures were low in each of three sites, but the tests extensively evaluated weeds and soilborne fungi management. Metam-sodium at 935 L ha−1 performed well in all three tests. The combination of metam-sodium (468 L ha−1) plus dichloropropene + 17% chloropicrin (126 L ha−1) provided good control of most of the pests and had high plant yield and vigor when covered with a polyethylene film immediately after treatment. A similar treatment not covered with polyethylene film but sealed with a mechanical soil cultipacker provided poor control of weeds. Stunting of tobacco and pepper was noted, especially in plots treated at the highest rates of metamsodium plus dichloropropene and chloropicrin. These treatments had a pungent odor associated with the treatment, which persisted for several weeks after polyethylene film removal. Many of the treatments, especially metam-sodium and metam-sodium in combination with dichloropropene and chloropicrin, compared well with methyl bromide fumigation for seedbed pest control.

The economics of strategies for control of root rot on chile (or chilli) peppers ( Capsicum annuum ) caused by Phytophthora capsici were analysed. The strategies investigated were alternate-row irrigation, every-row irrigation and chemical treatments with alternate-row irrigation. The chemical treatments were metam-sodium, copper sulfate and metalaxyl. Three years of data, 1989–1991, were analysed for green chile, and four years of data, 1988–1991, for red chile. The linear programming model results indicated that, to maximize returns to fixed resources without regard to risk, all resources should be allocated to every-row irrigation in 1989 and 1990 and when yields across all 4 years are considered. In 1988 and 1991, the yield benefits of alternate-row irrigation justified the cost of building the borders, although in 1988 every-row irrigation was not evaluated. For green chile, the optimal strategy was alternate-row irrigation in 1989, 1990, 1991 and when yields across all years are considered. The quadratic programming model showed that to reduce variance of returns in red chile production, alternate rows should be watered and copper sulfate applied via the irrigation water. To reduce variance of returns in green chile production, alternate-row irrigation with metalaxyl is recommended. Sensitivity analysis conducted on chile prices and labour and chemical costs showed that the optimal farm plans were insensitive to changes of 15% above and below the market prices and costs.

Field experiments were conducted to test the effects of alternate-row irrigation, every-row irrigation, and chemical treatments with alternate-row irrigation on yield of chile (chilli) peppers ( Capsicum annuum ) and disease incidence of chile pepper root rot caused by Phytophthora capsici . Field trials were conducted in 1989 and 1990 near Las Cruces, New Mexico. In 1989, chemical treatments were Telone C-17, metalaxyl, copper sulphate and metam-sodium; in 1990, chemical treatments were copper sulphate and metam-sodium. Disease incidence in plots receiving alternate-row irrigation without fungicides was significantly less than irrigation of every row without fungicides in 1989 and 1990. Disease incidence was also significantly less in the metam-sodium and metalaxyl plots than the every-row irrigated plots in 1989, but not significantly less than control plots irrigated with alternate rows without chemicals. Yield of red chile was significantly higher in plots treated wth metam-sodium and given alternate-row irrigation than all other treatments in 1989. Yield of green chile pepper from plots given alternate-row irrigation was significantly higher than plots given every-row irrigation in 1990. Metam-sodium with alternate-row irrigation was as good as, or better than, alternate-row irrigation alone in reducing disease incidence of P. capsici and in increasing yield.

With computation models, soil fumingation with metam-sodium under different conditions was simulated. Effectiveness was rated on the basis of computed cumulative concentration time products for methyl isothiocyanate in the water phase at various depths in the soil profile. Optimum soil moisture contents were in the dry part of the favourable range. With cold soil, soil fumigation might be effective but the fumigant may persist for several months.