Metam Research Articles

Soil Fumigation with Metam Sodium to Control Potato Scab

Soil Fumigation with Metam Sodium to Control Potato Scab

Chemical and physical alternatives to methyl bromide for soil disinfestation: results against soilborne diseases of protected vegetable crops.

SUMMARY In three experimental trials carried out in north Italy the effectiveness of methyl bromide (MB) and metham sodium (MS) applied alone or, at half dosages, in combination with a 2 week period of soil solarization against Rhizoctonia solani, Fusarium oxysporum f.sp. basilici and Colletotrichum gloeosporioides under greenhouse conditions were evaluated on crops such as basil, bean and lettuce. MB, at 30 g m -2 under virtually impermeable film confirmed its efficacy; covering the soil after the application of half dosage of MS with low density polyethylene films improved the efficacy of the treatment, while reducing some of the negative features. The combination of soil solarization with any of the two tested fumigants at reduced dosage resulted in an effective control of the tested pathogens, permitting a reduction in the duration of solarization and application of the fumigants at half dosage. Such strategy proved effective also on subsequent crops.

Influence of metam sodium on the dissipation and residual biological activity of the herbicides EPTC and pebulate in surface soil under black plastic mulch.

Metam sodium is a potential replacement for methyl bromide, which is used to control soil pests. Metam sodium rapidly breaks down in the soil to form methylisothiocyanate (MITC). Dissipation of the herbicides EPTC and pebulate in a silt loam soil under plastic mulch in the absence and presence of metam sodium was examined in field experiments in 1998 and 1999 at Knoxville, Tennessee. EPTC half-life (DT(50)) was 9 d, but when applied in conjunction with metam sodium DT(50) increased to 22 d. Similarly, average pebulate DT(50) was 8 d and increased to 23 d when applied in conjunction with metam sodium. This increase in herbicide DT(50) with the addition of metam sodium is thought to be due to a reduction in soil microorganisms that degrade EPTC and pebulate. EPTC applied with metam sodium injured tomato plants and reduced total crop yield more than EPTC, pebulate, or pebulate with metam sodium. The increased tomato injury may have been related to the greater and prolonged activity of EPTC and slower EPTC dissipation in the presence of metam sodium or MITC.

Effect of Soil Solarization and Cover Crops on Populations of Selected Soilborne Plant Pathogens in Western Oregon.

Field experiments were conducted in silty-clay loam in Corvallis, OR during the summers of 1995 and 1996 to study the effects of green manure cover crops (Sudan grass, rape, and barley), soil solarization, soil fumigation, and combinations of those treatments on population densities of soil pathogens Verticillium dahliae, Phytophthora cinnamomi, Pratylenchus penetrans, and Agrobacterium rhizogenes. Nylon mesh bags containing soil infested with V. dahliae and Phytophthora cinnamomiwere buried 5, 10, 20, and 30 cm deep. Soil solarization was performed over a 54- to 59-day period using a 0.6-mil clear polyethylene film. Maximum soil temperatures recorded at depths of 5, 10, 20, and 30 cm were 53, 48, 39, and 34°C in solarized soil, respectively; these temperatures were 8 to 16°C higher than in corresponding nonsolarized plots. Soil samples were collected before, during, and after solarization to quantify pathogen populations at those four depths. Pot or field studies were conducted subsequent to treatments to determine the effects of treatments on susceptible plants. Soil solarization, cover crops plus solarization, or fumigation with metam sodium resulted in a significant decrease (P< 0.05) in density of P. cinnamomi populations at all four depths and reduced (P< 0.05) V. dahliae at 5 and 10 cm. In greenhouse assays of solarized soils, disease severity was reduced (P< 0.05) for Verticillium spp. on eggplant and Phytophthora spp. on snapdragons. Cover crops alone were not effective in reducing P. cinnamomi and V. dahliae populations. Agrobacterium spp. population densities declined within solarized plots and incidence of crown gall on 'Mazzard' cherry rootstock planted in solarized plots was reduced significantly. Population densities of Pratylenchus penetranswere reduced in the upper 30-cm soil profile by solarization.Solarization for an 8-week period during the warmest months of summer could provide an additional management alternative for several important soilborne pathogens in western Oregon.

Fumigation with Chloropicrin, Metham Sodium, and EPTC as Replacements for Methyl Bromide in Southern Pine Nurseries

Abstract The effects of soil fumigation with chloropicrin alone or in combination with metham sodium and or with EPTC on the growth of loblolly pine (Pinus taeda L.) seedlings and on nutsedge (Cyperus spp.) control were investigated at three forest tree nurseries. Fumigation with chloropicrin plus metham sodium (CMS) significantly increased seedling numbers and growth compared to controls. Averaged among nurseries, mean root-collar-diameter increased from 0.14 to 0.17 in., and biomass from 0.14 to 0.20 lb/ft2. This produced seven more plantable seedlings and 6.5 more grade 1 seedlings/ft2 in CMS compared to not fumigated plots. Fumigation increased average potential sales $7,100/ac and increased present values, projected for the growth increases for additional grade 1 seedlings, by $25,900/ac. Fumigation increased biomass per unit area similarly at tested bed densities (10 to 29/ft2), but at low bed densities (≤20/ft2) the present values associated with grade 1 seedlings increased more than at higher densities. South. J. Appl. For. 24(3):135-139.

Advantageous attributes of larval whitefringed weevil, Naupactus leucoloma (Coleoptera: Curculionidae) for bioassaying soil fumigants, and responses to pure and plant-derived isothiocyanates.

First instars of the soil-inhabiting whitefringed weevil, Naupactus leucoloma (Boheman), are a particularly good bioassay model for assessing volatile soil fumigants and biofumigants. Eggs are readily obtained and can be stored for long periods with larvae hatched on demand and the first instar is non-feeding, surviving without food or shelter. Longevity varies with temperature, but readily accommodates the period required to conduct bioassays without appreciable mortality of untreated controls. In vitro bioassays of pure methyl isothiocyanate, the active ingredient from metham sodium soil fumigant, and the less volatile 2-phenylethyl isothiocyanate, sensitively detected differences in toxicity and effects of temperature. Bioassay of volatiles emitted from hydrolysed tissue of various isothiocyanate-producing Brassica plants revealed widely varying toxicity effects, indicating that bioassays with N. leucoloma are a sensitive and relevant indicator of the potential of different plants for biofumigation of soil-borne pest organisms.

The influence of metam sodium on soil respiration

A laboratory experiment was performed in order to evaluate the extent to which metam sodium (MS) applied at two different recommended rates and its degradation product, methyl isothiocyanate ( MITC ), affect soil respiration. Results suggest that MS degradation to MITC was complete within 4 hours and that MITC decomposed quickly in a few days, except in the soil containing high organic matter where it was still present after 15 days. Following the addition of MS, a lag phase appeared in CO2‐C evolution in the soil. It was longer for the higher dose of MS added and for the two soils with low organic C content. The dynamics of the process was described by the Bonde and Rosswall model and by the Gompertz RS E model for the untreated and the MS‐treated soils, respectively.

Metam Sodium Use in Vidalia Sweet Onions

Metam sodium has been evaluated on onions in Georgia since the mid-1980s for control of various soil pathogens in the production of transplants. Observations also indicated excellent weed control activity. Further work showed significant growth response of transplants, 90% or better weed control, and efficacy of Phoma terrestris, Fusarium, and Pythium. Results were better in comparison studies than found with methyl bromide, chloropicrin, and other fumigation combinations. This led to use of the product in field production of dry bulb onions. Seven years of studies revealed an average yield increase of 190 bushels per acre over the control, even where Phoma terrestris levels were minimal. Today, almost all transplant production includes the use of metam sodium and field use is beginning to be used by growers. With limited crop rotation being practiced in the Vidalia onion belt, metam sodium will continue to play a major role in controlling the ever-increasing levels of Phoma terrestris and maintaining profitability in onion production in Georgia.

Combined Soil Treatments and Sequence of Application in Improving the Control of Soilborne Pathogens

ABSTRACT The effects of reduced doses of methyl bromide (MB) or metham sodium, heating, short solarization, and soil microbial activity, alone or in combination, on survival of soilborne fungal pathogens were tested in a controlled-environment system and field plots. Sublethal doses of heating or MB delayed germination of Sclerotium rolfsii sclerotia. Combining MB and heating treatments was more effective than either treatment alone in controlling S. rolfsii and Fusarium oxysporum f. sp. basilici. The application heating followed by fumigation with MB, was significantly more effective in delaying and reducing germination of S. rolfsii sclerotia and in controlling F. oxysporum f. sp. basilici than the opposite sequence. Further, incubation in soil and exposure to microbial activity of previously heated or MB-treated sclerotia increased the mortality rate, indicating a weakening effect. Similarly, incubation of chlamydospores of F. oxysporum f. sp. melonis and F. oxysporum f. sp. radicis-lycopersici in soil in the field after fumigation further reduced their survival, confirming the laboratory results. In field tests, combining MB or metham sodium at reduced doses with short solarization was more effective in controlling fungal pathogens than either treatment alone. Treatment sequence significantly affected pathogen control in the field, similar to its effect under controlled conditions. This study demonstrates a frequent synergistic effect of combining soil treatments and its potential for improving pathogen control and reducing pesticide dose, especially when an appropriate sequence was followed.

029 Synergism of Fumigant Combinations for Nutsedge Control

As of 2005, methyl bromide will no longer be produced or imported for agricultural use in industrialized countries. The uncertain future of methyl bromide as a soil fumigant has stimulated research into the use of other soil fumigants for weed control. Laboratory experiments were conducted to determine the efficacy of methyl bromide (MB), methyl iodide (MI), propargyl bromide (PB), 1,3-dichloropropene (1,3-D), and metham sodium (MS) alone and in combination with chloropicrin (PIC) against Cyperus esculentus L (yellow nutsedge). The experimental design was a randomized complete block with three replications. All experiments were repeated. Tubers were imbibed for 24 h and mixed with soil adjusted to 14% moisture (w/w). Soil/tuber samples were fumigated for 48 h with MB, MI, 1,3-D, and PIC at 0.0, 3.1, 6.3, 12.5, 25, 50, 100, and 200 μm of active ingredient. Samples were fumigated with PB and MS at 0.0, 0.8, 1.6, 3.1, 6.3, 12.5, 25, and 50 μm of active ingredient. After fumigation and venting, each soil/tuber sample was wetted and placed in a Petri plate for 5 days. Shoot emergence was recorded. Additionally, to determine synergism response with PIC, 17% PIC was added to each fumigant/rate combination. Fumigation and data collection were performed as described above. Dose-response curves were constructed to determine the effective dose to control 50% of nutsedge emergence (ED50). PB and MS were the most efficacious fumigants with ED50's of 3.7 and 6.5 μm, respectively. EC50 values for all the fumigants were significantly lower than MB except for 1,3-D. All the fumigant-PIC combinations resulted in synergistic control of nutsedge.

511 Diagnosis and Management Strategies for Soilborne Apple Replant Problems in New York Orchards

We are evaluating the severity of apple replant disease (ARD)-characterized by stunted tree growth in replanted orchards, attributed to root pathogens and/or edaphic conditions-and testing preplant soil treatments for control of this wide-spread problem. Soil samples were collected during 1996–98 at 17 orchards in New York's major fruit growing regions and plant-parasitic nematodes and nutrient availability were quantified. Apple seedlings and potted trees on M.9 rootstocks were grown in fumigated and non-fumigated soil samples as a diagnostic bioassay for ARD severity. Factorial combinations of metam sodium, consecutive cover crops of Brassica juncea `Forge' and Sorghum sudanense `Trudan 8', and fertilizer/lime amendments were applied as preplant treatments at each orchard, 9 to 12 months before trees were replanted. Diagnostic bioassays indicated severe ARD at more than half the sites, and nematodes were not a major factor. Responses to preplant soil treatments were highly variable across the 17 farms. The best tree growth and yields followed preplant metam sodium at some sites, Brassica juncea and Sorghum sudanense at others, or fertilizer amendments at a few others. Tree responses to combined preplant soil treatments were often additive, and greater at irrigated sites. Comparisons of preplant diagnostic bioassay results with subsequent tree responses to metam sodium at the 17 orchards indicated that diagnostic tests predicted from 7% to 75% of tree growth response to soil fumigation, varying substantially across years and sites. It appeared that ARD was variable and site specific in New York orchards, and could not be controlled effectively with a uniform preplant soil treatment across our major fruit-growing regions.

695 Weed Control in Minor Crops After the Loss of Methyl Bromide

The economics of pesticide production and registration has limited the number of pesticides registered for use in minor crops relative to agronomic crops. Current regulations such as the Food Quality Protection Act may further reduce the number of efficacious compounds registered for use on minor crops. Traditionally, the lack of registered pesticides for minor crops has been offset by soil fumigation. However, methyl bromide use is scheduled for phase-out in the United States by 2005, leaving a pest control vacuum in some crops. Loss of methyl bromide has stimulated research into the use of other soil fumigants for weed control. Methyl bromide, methyl iodide, propargyl bromide, 1,3-dichloropropene, and metham sodium have been tested alone and in combination with chloropicrin in laboratory experiments to determine their efficacy against Cyperus esculentus L (yellow nutsedge) tubers. All the fumigants controlled nutsedge equal to or better than methyl bromide and resulted in synergistic control when combined with chloropicrin. Although excellent weed control can be achieved with all the fumigants in the laboratory, weed control in the field with the same fumigant may result in poor or no control. Further research is necessary to optimize the field application of the remaining fumigants to maximize pest control. In the near future, to achieve the broad-spectrum pest control obtained with methyl bromide, growers will need to rely on multiple control strategies. The most promising replacement program for broad-spectrum pest control includes dichloropropene/chloropicrin fumigation followed by a herbicide program or mechanical weed control. To control problem weeds that are not controlled with the in-season herbicide program, a chemical fallow program should be instituted in the off-season to reduce weed pressure during the cropping season.

Broccoli residues can control Verticillium wilt of cauliflower

Verticillium wilt, a damaging disease of cauliflower, was successfully managed in a multiple-year field study by incorporating broccoli residues into infested soil. In a study conducted from 1993 to 1995 in the Salinas Valley, cauliflower disease incidence and severity were consistently and significantly reduced in the broccoli residue plots when compared with no broccoli. The commercial standard plots fumigated with methyl bromide + chloropicrin had the lowest disease incidence and severity. In both years of our tarping study, Verticillium wilt severity was lowest in the metham sodium treatment. The cauliflower-Verticillium host-pathogen system therefore can act as a model for controlling soil-borne diseases without the use of synthetic chemicals.

Impact of chemical, biological and cultural treatments on the growth and yield of apple in replant-disease soil.

An orchard experiment was established to determine the long-term (six year) effects of chemical (sodium methyldithiocarbonate — metam sodium), fertiliser (monoammonium phosphate) and biological agents [strain B8 of Enterobacter agglomerans, strain EBW-4 of Bacillus subtilis and Glomus intraradices (GI)] alone and in selected combinations on tree growth, fruit production and root rot incidence of apple trees in apple-replant-disease soil that was conducive to replant disease over six years. The response was measured by increases in trunk cross-sectional area, fruit yield and percent root rot of Gala apple trees on M.9 rootstock. The application of E. agglomerans (B8), B. subtilis (EBW-4), G. intraradices (GI), metam sodium (MS), MS + B8, MS + GI and B8 + EBW-4 significantly increased fruit yield, tree trunk growth and reduced infection by Phytophthora cactorum and Pythium ultimum. These results suggest the potential use of E. aerogenes (B8), B. subtilis (EBW-4) and G. intraradices to increase growth and fruit production of apple trees planted in soil conducive to replant disease.

A Meta-analysis of Strawberry Yield Response to Preplant Soil Fumigation with Combinations of Methyl Bromide–chloropicrin and Four Alternative Systems

Yield for annual California strawberry (Fragaria ×ananassa Duch.) production systems in soils treated with combinations of methyl bromide–chloropicrin (MB:CP) were compared with four alternative soil treatment systems using meta-analysis. Studies represent 11 production seasons, and were conducted at three distinct locations in California. Fumigation with mixtures of methyl bromide (MB) and chloropicrin (CP) increased yield significantly compared with any and all alternatives lacking MB. In a combined analysis of 45 studies, fumigation with MB:CP compounds increased yield an average of 94.4% (d+ = 2.874 ± 0.098) compared with yields for plants in nonfumigated (NF) soils. Further, the effect of MB:CP fumigation increased over the first three strawberry cultivation cycles: MB:CP–fumigated soils provided a 59.2% (d+ = 2.166 ± 0.146) yield advantage when one cycle of fumigation was omitted, a 100.2% (d+ = 3.000 ± 0.143) advantage when two cycles were omitted, and a 148.4% (d+ = 6.201 ± 0.348) yield advantage when three or more cycles of MB:CP were omitted. In a combined analysis that included 34 studies, soil fumigation with MB:CP conferred a 9.6% (d+ = 0.751 ± 0.087) yield advantage over fumigation with CP alone. Soils treated with MB:CP yielded 6.8% (d+ = 0.437 ± 0.114) more fruit than those treated with very high rates of CP (336–396 kg·ha–1), and 15.4% (d+ = 1.190 ± 0.134) more than soils treated with commercially realistic rates (168–224 kg·ha–1). Similar to the comparison using NF soils, the efficacy of very high rates of CP appeared to diminish over cycles of strawberry cultivation; MB:CP increased yield 2.2% (d+ = 0.043 ± 0.162) in the first CP production cycle, 10.6% (d+ = 0.588 ± 0.174) and 13.7% (d+ = 2.054 ± 0.401) in the following two cycles. Combinations of dichloropropene (DP) and CP were no more effective than were lower rates of CP alone, and MB:CP conferred a 14.4% (d+ = 0.962 ± 0.162) yield advantage over mixtures of DP:CP. Mixtures of MB:CP increased yield 29.8% (d+ = 3.199 ± 0.287) compared with metam sodium (MS). The standardized effect was similar when comparing MB:CP combinations with either MS or NF soils, suggesting little effect of MS on the yield response. Chemical names used: trichloronitromethane (chloropicrin); 1,3-dichloropropene (dichloropropene); sodium N-methyldithiocarbamate (metam sodium).

Biological Suppression and Natural Population Decline ofHeterodera schachtiiin a California Field

ABSTRACT Soil suppressiveness to Heterodera schachtii was demonstrated in a field at the research station of the University of California, Riverside. In two field trials planted to Swiss chard (Beta vulgaris), introduced H. schachtii multiplied 2.7 and 1.7 times more in preplant metam sodium-fumigated plots than in nontreated plots in 1994 and 1995, respectively. In greenhouse experiments, preplant treatments with metam sodium, methyl bromide, methyl iodide, formaldehyde, and aerated steam reduced suppressiveness of soil against H. schachtii to undetectable levels. H. schachtii multiplied significantly less in nontreated soil than in treated soil on Swiss chard. At harvest, the number of infective second-stage juveniles in suppressive soil was close to the lowest detection level, whereas high numbers were encountered in soils initially treated. In a crop rotation trial with host crops of H. schachtii, introduced H. schachtii populations were monitored for five cropping periods over 30 months in initially fumigated versus nontreated suppressive field plots. In fumigated plots, H. schachtii population levels increased in the first and second cropping periods and then declined in the third cropping period. In the fourth and fifth cropping periods, the nematode reproduction factor in the initially fumigated plots was not significantly different from that in suppressive plots.

Impact of fumigation with metam sodium upon soil microbial community structure in two Japanese soils

The effects of fumigation with sodium methyl dithiocarbamate (metam sodium) on the microbial community structure and function in 2 soils were investigated using a variety of techniques. In both soils ca. 50% and 90% of the populations of total and culturable bacteria, respectively, were killed by fumigation, with recovery to levels prevailing in control soils 26 d after cessation of fumigation. The size of the ammonium and nitrite oxidiser populations was reduced by up to 4 orders of magnitude by fumigation, with the latter showing a slight recovery 105 d later. There were substantial changes in the C-utilisation (Biolog GN) profiles in the fumigated soils even 105 d later. The number and pattern of amplified 16S ribosomal DNA restriction analysis (ARDRA) fragments was changed by fumigation, and there was a shift in the %G+C profile toward a greater proportion of lower %G+C classes in treated soils. It appeared that DNA released from killed cells remained for some time after fumigation, and masked the apparent community DNA profiles. This study demonstrates that the effects of fumigation on the soil microbial community structure and function were pronounced and for some parameters very persistent. However, the effects on broad-scale properties such as total or culturable bacterial numbers were less enduring.

Evaluation of Broccoli Residue Incorporation into Field Soil for Verticillium Wilt Control in Cauliflower.

Wilt incited by Verticillium dahliae has recently become an important disease on cauliflower in the Salinas Valley. Although broccoli is closely related to cauliflower, wilt has not occurred on this host and V. dahliae isolates from cauliflower were weakly pathogenic on broccoli in greenhouse inoculations. In this study, the effectiveness of broccoli residues on propagule attrition in soil and wilt incidence on cauliflower was determined in a commercial field infested with V. dahliae microsclerotia. The treatments were broccoli residue with tarp, broccoli residue without tarp, chloropicrin, metham sodium, control with tarp, control without tarp, cauliflower followed by cauliflower, and cauliflower followed by fallow. Approximately 200 kg of chopped broccoli was uniformly disk incorporated into the corresponding plots (36 m2). Densities of V. dahliae microsclerotia were determined at 0, 30, 90, and 145 days after treatment in 1993 and 0, 30, 74, 109, and 140 days after treatment in 1994 using the modified Anderson sampler technique. Cauliflower cultivar White Rock was planted in all plots. Plant height, number of marketable heads, head weight, and wilt severity were determined at maturity. Even though the pre-treatment number of V. dahliae propagules in broccoli-treated and control plots were similar, by the end of the cauliflower cropping season numbers either were the same or increased in control plots compared with a reduction in numbers in broccoli residue-treated plots during both seasons. There were no differences between tarped and non-tarped plots either in broccoli residue-treated or control plots. In fumigated plots, propagules declined initially but later returned to pre-treatment levels by the end of the cropping season. Continuous cauliflower or fallowing after one cauliflower crop resulted in stable or increased levels of microsclerotia. Verticillium wilt severity was lowest in metham sodium-treated plots, followed by broccoli residue-treated plots and chloropicrin in both years. Plant height, marketable heads, and head weight were higher in broccoli-treated than in control plots. These results suggest that broccoli residues reduce V. dahliae microsclerotia in soil and wilt of cauliflower as much as or more than chloropicrin and metham sodium, and that rotation with broccoli may be a feasible approach to manage Verticillium wilt in cauliflower and other susceptible crops.

Effect of methyl bromide, metham sodium and the biofumigants Indian mustard and canola on the incidence of soilborne fungal pathogens and growth of grapevine nursery stock

The potential of the biofumigant crops Indian mustard and canola (cv. Dunkeld) to replace methyl bromide (MeBr) and metham sodium for the control of root pathogens on Shiraz on Ramsey rootstocks was evaluated in a commercial grapevine nursery in the Riverland district of South Australia. The application of MeBr and metham sodium resulted in a significant 78% and 40% increase, respectively, in the percentage of first grade vines at harvest. In contrast, Indian mustard and canola incorporated into the soil at equivalent rates of 12.2 and 9.8 t dry matter per ha, respectively, had no significant effect upon the percentage of first grade vines. There was a significant reduction in vine establishment in the plots treated with Indian mustard (87.5%), compared to the control (93.5%). This reduction was related to a significant increase in the number of Pythium propagules in soil in the plots treated with Indian mustard and canola. Pythium spp. were isolated from >86% of stunted vines in the brassica amended plots. MeBr and metham sodium caused significant reductions in the number of Pythium propagules in the soil and caused significant reductions in the incidence of Cylindrocarpon spp. and Rhizoctonia spp, in the first grade vine roots at harvest. These results demonstrate that, at the rates of incorporation, Indian mustard and canola were unable to replace the beneficial effects and economic returns of MeBr or metham sodium on nursery grapevine growth.

Evaluation of Methyl Iodide as a Soil Fumigant for Root-Knot Nematode Control in Carrot Production

Methyl iodide performance as a soil fumigant was compared with methyl bromide for Meloidogyne incognita control in carrot production. Both compounds were applied to tarped beds by hot-gas fumigation in growers' fields near Bakersfield, California. Methyl iodide was applied at 112, 168, 224, and 336 kg ha-1 and methyl bromide at 112 and 224 kg ha-1. Other chemical treatments included a non-fumigated control, metam sodium (373 liters ha-1), applied through overhead irrigation, and 1,3-dichloropropene (1,3-D; 112 liters ha-1) commercially shank applied. Soil was either extracted or bioassayed with tomato plants to determine M. incognita populations prior to application of fumigants, 2 weeks after fumigant application, and at carrot harvest. Carrots were rated for marketability based on size and ematode-induced damage. Methyl bromide, methyl iodide, and 1,3 D were effective at reducing M. incognita populations over the season at all rates tested. In both trials, plants in plots fumigated with either methyl bromide or methyl iodide produced at least 161 and 181% more marketable carrots without nematode damage, respectively, than plants in control plots. Methyl iodide was an effective alternative to methyl bromide for nematode control in carrot production.