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S.J. Locascio, J.P. Gilreath, D.W. Dickson, T.A. Kucharek, J.P. Jones, and J.W. Noling

Tomato (Lycopersicon esculentum Mill.) was grown to evaluate various chemicals as possible alternatives to methyl bromide as a soil fumigant. Due to pest pressures from weeds, nematodes, and soil fungi, the use of a broad-spectrum fumigant is essential for economical tomato production. Methyl bromide (MBr) is the fumigant of choice for most growers using polyethylene mulch culture. In 1991, MBr was identified to be in a group of chemicals allegedly responsible for depletion of the stratospheric ozone layer. The U.S. Environmental Protection Agency (EPA) has since called for a phaseout of MBr by the year 2001. At several locations in Florida, alternative soil fumigants were evaluated including 98% MBr-2% chloropicrin (Pic) at 450 kg·ha–1, 67% MBr 33% –Pic (392 kg·ha–1), Pic (390 kg·ha–1), 1,3-dichloropropene + 17% Pic (1,3-D+C17) at 327 L·ha–1, and metham sodium (935 L·ha–1). Metham sodium was also applied by drip irrigation as well as enzone (1870 L·ha–1). Dazomet (448 kg·ha–1) was surface applied and incorporated. Pebulate (4.5 kg·ha–1) was incorporated with some treatments. Pic and 1,3-D+C17 treatments provided control of nematodes and soil fungi. With the addition of pebulate, some nutsedge control also was obtained. Tomato fruit yields with 1,3-D+C17 + pebulate and with Pic + pebulate ranged from 86% to 100% of that obtained with MBr treatments. Pest control and crop production were lower with the other treatments than with the above combinations and with MBr. These studies indicate that no one pesticide can provide the broad spectrum control provided by MBr.

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Salvadore J. Locascio, James P. Gilreath, D.W. Dickson, Thomas A. Kucharek, J.P. Jones, and J.W. Noling

Tomato (Lycopersicon esculentum Mill.) was grown to evaluate various chemicals as possible alternatives to methyl bromide soil fumigation. Due to a combination of weeds, nematodes, and soil fungi, the use of a broad-spectrum fumigant has been essential for economical tomato production in Florida. Methyl bromide (MBr) and combinations of MBr with chloropicrin (Pic) are the fumigants of choice for most growers using polyethylene mulch culture. In 1991, MBr was allegedly associated with stratospheric ozone depletion. The U.S. Environmental Protection Agency has since mandated a phaseout of MBr for soil fumigation in the United States by the year 2001. At three locations in Florida, alternative soil fumigants were evaluated, including soil injected 98% MBr—2% Pic at 450 kg·ha-1, 67% MBr—33% Pic (390 kg·ha-1), Pic (390 kg·ha-1), dichloropropene + 17% Pic (1,3-D + Pic) at 327 L·ha-1, and metam-sodium (935 L·ha-1). Also, metam-sodium and tetrathiocarbonate (1870 L·ha-1) were applied by drip irrigation. Dazomet (450 kg·ha-1) was surface applied and soil incorporated. Pebulate (4.5 kg·ha-1) was soil incorporated with some treatments. Pic and 1,3-D + Pic treatments provided good to moderate control of nematodes and soil fungi except in one of the six studies, in which nematode control with 1,3-D was moderate to poor. Nutsedge densities were suppressed by addition of pebulate. Tomato fruit yields with 1,3-D + Pic + pebulate and with Pic + pebulate at the three sites ranged from 85% to 114%, 60% to 95%, and l01% to 119%, respectively, of that obtained with MBr treatments. Pest control and crop yield were lower with treatments other than the above pebulate-containing or MBr-containing treatments. These studies indicate that no one alternative pesticide can provide the consistent broad-spectrum control provided by MBr. Chemical names used: trichloronitromethane (chloropicrin); 1,3-dichloropropene (1,3-D); sodium N-methyldithiocarbamate (metam-sodium); sodium tetrathiocarbonate (tetrathiocarbonate); 3,5-dimethyl-(2H)-tetrahydro-l,3,5-thiadiazine-2-thione (dazomet); S-propyl butyl(ethyl)thiocarbamate (pebulate).

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Grant R. Manning and Steven A. Fennimore

Methyl bromide has been the foundation of chemical weed control in strawberry (Fragaria ×ananassa) in California for over 40 years. The impending phaseout of methyl bromide may leave strawberry producers dependent on less efficacious alternative fumigants for weed control. The use of herbicides to supplement fumigants is a potential weed control strategy for strawberry. A 2-year field study was conducted in California to evaluate 10 herbicides as possible supplements for methyl bromide alternative fumigants. Herbicides were applied immediately after transplanting (immediate posttransplant), and 3 weeks after transplanting (delayed posttransplant). Napropamide applied immediate posttransplant was included as a commercial standard. Immediate posttransplant treatments that were safe in strawberry include carfentrazone at 0.075 and 0.15 lb/acre (0.084 and 0.168 kg·ha-1), flumioxazin at 0.063 lb/acre (0.071 kg·ha-1) and sulfentrazone at 0.175 and 0.25 lb/acre (0.196 and 0.28 kg·ha-1). Triflusulfuron at 0.016 lb/acre (0.017 kg·ha-1) was the only delayed posttransplant treatment with acceptable selectivity. Among the selective herbicides applied immediate posttransplant, flumioxazin and napropamide provided the most consistent control of bur clover (Medicago polymorpha) and shepherd's purse (Capsella bursa-pastoris). Triflusulfuron applied delayed posttransplant did not significantly reduce bur clover densities, but did reduce shepherd's purse densities.

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Husein A. Ajwa and Thomas Trout

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).

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S.A. Fennimore, M.J. Haar, and H.A. Ajwa

The loss of methyl bromide (MB) as a soil fumigant has created the need for new weed management systems for crops such as strawberry (Fragaria ×ananassa Duchesne). Potential alternative chemicals to replace methyl bromide fumigation include 1,3-D, chloropicrin (CP), and metam sodium. Application of emulsified formulations of these fumigants through the drip irrigation system is being tested as an alternative to the standard shank injection method of fumigant application in strawberry production. The goal of this research was to evaluate the weed control efficacy of alternative fumigants applied through the drip irrigation system and by shank injection. The fumigant 1,3-D in a mixture with CP was drip-applied as InLine (60% 1,3-D plus 32% CP) at 236 and 393 L·ha-1 or shank injected as Telone C35 (62% 1,3-D plus 35% CP) at 374 L·ha-1. Chloropicrin (CP EC, 95%) was drip-applied singly at 130 and 200 L·ha-1 or shank injected (CP, 99%) at 317 kg·ha-1. Vapam HL (metam sodium 42%) was drip-applied singly at 420 and 700 L·ha-1. InLine was drip-applied at 236 and 393 L·ha-1, and then 6 d later followed by (fb) drip-applied Vapam HL at 420 and 700 L·ha-1, respectively. CP EC was drip-applied simultaneously with Vapam HL at 130 plus 420 L·ha-1 and as a sequential application at 200 fb 420 L·ha-1, respectively. Results were compared to the commercial standard, MB : CP mixture (67:33) shank-applied at 425 kg·ha-1 and the untreated control. Chloropicrin EC at 200 L·ha-1 and InLine at 236 to 393 L·ha-1 each applied singly controlled weeds as well as MB : CP at 425 kg·ha-1. Application of these fumigants through the drip irrigation systems provided equal or better weed control than equivalent rates applied by shank injection. InLine and CP EC efficacy on little mallow (Malva parviflora L.) or prostrate knotweed (Polygonum aviculare L.) seed buried at the center of the bed did not differ from MB : CP. However, the percentage of weed seed survival at the edge of the bed was often higher in the drip-applied treatments than in the shank-applied treatments, possibly due to the close proximity of the shank-injected fumigant to the edge of the bed. Vapam HL was generally less effective than MB : CP on the native weed population or on weed seed. The use of Vapam HL in combination with InLine or CP EC did not provide additional weed control benefit. Chemical names used: 1,3-dichloropropene (1,3-D); sodium N-methyldithiocarbamate (metam sodium); methyl bromide; trichloro-nitromethane (chloropicrin).

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S.D. Nelson, S.J. Locascio, L.H. Allen Jr., D.W. Dickson, and D.J. Mitchell

Methyl bromide (MeBr) is an important and effective soil fumigant commonly used to control weeds and soilborne pests. Because MeBr has been implicated as a contributor to the depletion of stratospheric ozone, it is scheduled for phaseout by 2005. This study examined nonchemical and chemical practices as alternatives to MeBr. Off-season flooding followed by a series of soil preplant chemical treatments [MeBr with 33% Pic; 1,3-D mixed with 17% (C-17) and 35% (C-35) Pic combined with Peb; and metam-Na combined with 1,3-D and Peb were evaluated on spring tomato (Lycopersicon esculentum Mill.) and eggplant (Solanum melongena) production in northern Florida. Pest control and tomato and eggplant yields were not significantly different between the flooded and non-flooded control plots. The most effective alternatives to MeBr were 1,3-D and Pic mixtures (C-17 and C-35) combined with Peb. Tomato and eggplant yields for these chemicals were statistically equivalent to that of MeBr. Tomato, but not eggplant, yield and nematode control were poor with metam-Na combined with 1,3-D and Peb in comparison to the other fumigant combinations. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitromethane [chloropicrin (Pic)]; S-propyl butyl(ethyl)thiocarbamate [pebulate (Peb)]; sodium N-methyldithiocarbamate (metam-sodium (metam-Na)].

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Olha Sydorovych, Charles D. Safley, Lisa M. Ferguson, E. Barclay Poling, Gina E. Fernandez, Phil M. Brannen, David M. Monks, and Frank J. Louws

Partial budget analysis was used to evaluate soil treatment alternatives to methyl bromide (MeBr) based on their cost-effectiveness in the production of strawberries (Fragaria ×ananassa). The analysis was conducted for two geographical areas: the piedmont and coastal plain area (including North Carolina and Georgia) and the mountain area of western North Carolina, based on 7 years of field test data. The fumigation alternatives evaluated were Telone-C35 (1,3-dichloropropene 61.1% + chloropicrin 34.7%), Telone II (1,3-dichloropropene 94%), chloropicrin (Chlor-o-pic 99% and TriClor EC), InLine (1,3-dichloropropene 60.8% + chloropicrin 33.3%), and metam sodium (Vapam or Sectagon 42, 42% sodium methyldithiocarbamate). The MeBr formulation was 67% MeBr and 33% chloropicrin (Terr-O-Gas) with the exception of the earlier trials where a 98:2 ratio was used. In the piedmont and coastal plain area, the soil treated with chloropicrin showed the best results with an additional return of $1670/acre relative to MeBr, followed by Telone-C35 with an additional return of $277/acre. The projected return associated with shank-applied metam sodium was approximately equal to the estimated return a grower would receive when applying MeBr. Fumigating with drip-applied metam sodium, InLine, and Telone II as well as the nonfumigated soil treatment resulted in projected losses of $2182, $2233, $4179, and $6450 per acre, respectively, relative to MeBr. In the mountain area, all of the alternatives resulted in a projected increase in net returns relative to MeBr. The largest projected increase was $1320/acre for the InLine treatment, while the added returns for the TriClor and Telone-C35 applications were estimated to be $509 and $339 per acre, respectively. The drip-applied metam sodium application resulted in an additional return of $40/acre, and the added revenue for the nonfumigated soil treatment was $24/acre more than MeBr treatment. Although technical issues currently associated with some of the alternatives may persist, results indicate that there are economically feasible fumigation alternatives to MeBr in the production of strawberries in the southeastern U.S.

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Bielinski M. Santos, José Manuel López-Aranda, James P. Gilreath, Luis Miranda, Carmen Soria, and Juan J. Medina

Tunnel and open field trials were conducted in two locations in Huelva, Spain, and one in Florida to determine the effect of selected methyl bromide (MBr) alternatives on strawberry yield. In Spain, the tunnel treatments were: a) nontreated control, b) MBr + chloropicrin (Pic) 50:50 at a rate of 400 kg·ha–1; c) dazomet at 400 kg·ha–1, d) 1,3-dichloropropene (1,3-D) + Pic 65:35 at 300 kg·ha–1; e) Pic at 300 kg/ha; f) dimethyl disulfide (DMDS) + Pic 50:50 at 250 + 250 kg·ha–1; and f) propylene oxide at 550 kg·ha–1. All treatments were covered with virtually impermeable film (VIF), except the nontreated control, which was covered with low-density polyethylene (LDPE) mulch. Dazomet was rototilled 10 cm deep, whereas the other fumigants were injected with four chisels per bed. In Florida, the open-field treatments were a) nontreated control, b) MBr + Pic 67:33 at a rate of 400 kg/ha with LDPE; c) MBr + Pic 67:33 at 310 kg·ha–1 with VIF; d) 1,3-D + Pic 65:35 at 300 kg·ha–1 with VIF; e) methyl iodide (MI) + Pic 50:50 at 230 kg·ha–1 with VIF; f) Pic at 300 kg·ha–1 with VIF; g) DMDS + Pic 50:50 at 250 + 250 kg·ha–1 with VIF; and g) propylene oxide at 500 kg·ha–1 with VIF. The fumigants were applied with three chisels per bed. In Spain, the results showed that 1,3-D + Pic, DMDS + Pic, and Pic consistently had similar marketable yields as MBr + Pic. Similar results were found in Florida, with the exception of propylene oxide, which also had equal marketable fruit weight as MBr + Pic.

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Mark Rieger, Gerard Krewer, and Pamela Lewis

Solarization and chemical alternatives to methyl bromide (MeBr) soil fumigation for strawberry (Fragaria {XtimesX} ananassa) were evaluated in a 3-year study in Savannah, Ga. Solarization using clear or black plastic, metam sodium (Sectagon), dazomet (Basamid), 1,3-dichloropropene and chloropicrin (Telone C-35), MeBr, and untreated control treatments were used. Solarization produced maximal soil temperatures of 55 to 60 °C (131 to 140 °F) at the 2.5 cm (1 inch) depth, and 42 to 48 °C (108 to 118 °F) at the 15 cm (6 inch) depth. Clear and black plastic were generally equally effective in heating the soil. A double layer of clear plastic raised soil temperatures 1 to 2 °C (2 to 4 °F) above those under a single layer of clear at the 2.5 cm depth, although this occurred less frequently at the 15 cm depth. MeBr treatment increased yield by 46% and 128% in the first and second years, respectively, compared to the untreated control, but all treatments were similar in yield in year three. Season average fruit size differed among treatments in only the first year, with MeBr resulting in fruit 13% to 25% larger than other treatments. Yield for the metam sodium treatment in the first year was 34% lower than for MeBr, but comparable to MeBr in the other 2 years. Solarization treatment yields were similar to those of MeBr in the first and third years, but could not be analyzed in the second year due to plot damage. Dazomet treatment yields were similar to those of MeBr, metam sodium, and the untreated control in its single year of testing, but logistics of application and high costs may disfavor this treatment. The 1,3-dichloropropene/chloropicrin treatment performed as well as MeBr in its single year of testing. Three treatments-metam sodium, 1,3-dichloropropene/chloropicrin, and solarization with black plastic-offer viable, lower cost alternatives to MeBr.

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Douglas C. Sanders, Luz M. Reyes, David W. Monks, Katie M. Jennings, Frank J. Louws, and Jim G. Driver

Compost sources were used to determine long-term influence on common vegetable cropping systems (tomato, pepper, and cucumber). Three sources of Controlled Microbial Compost (CMC) (20 yd3/A) amended with fumigant Telone-C35 (35 gal/A) and Trichoderma-382 [2.5 oz/yd.3 (T-382)] were used during 3 consecutive years. Tomato showed statistic differences (1%) among compost treatments with higher total yields when CMC was combined with Telone-C35 (21%) and T-382 (8.2%). All treatments but Bio-Compost and control presented al least 25% more marketable yield per acre. No differences in fruit size were found for tomato, except for medium-size fruit when Telone C-35 was added. The CMC alone or combined with Telone C-35 and T-382 increased the total plant dry weight at least 18.6%. Pepper crop showed statistic differences with higher number of No. 1 fruit size when CMC was combined with Telone C-35 and T-382. Number of culls per acre decreased for all three compost sources, with no differences from the control. Cucumber yields differed among treatments for total and marketable yields and No.1 size fruit per acre. Best yields were achieved with CMC and when mixed with Telone C-35 and T-382. The lower numbers of culls per acre were found with Bio-Compost and Lexington sources and CMC+T-382. Total plant dry weight was increased in at least 24% when Bio-Compost or CMC compost were used alone or combined with Telone-C35 or T-382. CMC increased root knot nematode soil counts and percentage of root galling, but tended to improve root vigor in cucumbers. It seems that compost sources combined with Telone C-35 or T-382 could improve the cropping management as alternative to methyl bromide. Weed responses will also be discussed.