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Douglas V. Shaw, Thomas R. Gordon, and Kirk D. Larson

Strawberry runner plants from the cultivar `Selva' (Fragaria ×ananassa Duch.) were produced using three nursery treatments in each of three years: propagation in soil fumigated with a mixture of 2 methyl bromide: 1 chloropicrin (w/w) at 392 kg·ha-1, propagation in fumigated soil but using planting stock inoculated prior to nursery establishment with a conidial suspension of Verticillium dahliae (106 conidia/mL), and propagation in nonfumigated soil naturally infested with V. dahliae. Runner plants were harvested and stored at 1 °C for 6, 18, or 34 days prior to establishment in fruit production trials. No significant differences were found between runner plants grown in naturally infested soil and runner plants obtained from artificially inoculated mother plants for V. dahliae infection rates detected by petiole isolation immediately prior to transplanting, the percentage of plants visibly stunted due to disease during the following production season, and seasonal yield compared with corresponding noninfected controls. Cold storage of runner plants for 18 or 34 days, produced using either natural or artificial inoculation systems, reduced the initial percentage of infected plants by 42% to 61% and the percentage of stunted plants during the following fruit production season by 43% to 57%, compared with plants from corresponding nursery treatments given only 6 days post-nursery cold storage. Yields for inoculated plants with 6 days cold storage were 16% to 20% less than those for uninoculated controls, whereas yields for inoculated plants with 18 or 34 days of storage were 3% to 9% less than the respective controls. Most of the cold storage effects on initial infection rate, stunting, and yield were realized at the 18 days of storage treatment. A reduction in the fraction of V. dahliae infected plants due to cold storage, suggests either a direct effect of cold storage on the disease organism or stimulation of secondary resistance mechanisms in the plant. Chemical name used: trichloronitromethane (chloropicrin).

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Kirk D. Larson

Replant soil fumigation with mixtures of methyl bromide (MeBr) and chloropicrin (trichloronitromethane) is a standard practice for pest and disease control in fruit crop nurseries in California. The proposed phase-out of MeBr by the year 2001 requires that alternative soil sterilants be studied for nursery use. Therefore, on 5 April, 1993, three preplant soil treatments were applied to new strawberry ground: 1) MeBr/chloropicrin (67:33) at 392 kg/ha: 2) chloropicrin, a possible MeBr substitute. at 140 kg/ha: and 3) nonfumigation. The experimental design was a RCB: there were two plots (each 10′ × 15′) for each of two cultivars (`Chandler' and `Selva') for the 3 soil treatments in each of 3 blocks. Mother plants were planted 26 April, and plots were machine-harvested in October, 1993. All plants from each plot were uniformly graded, after which mean stolon yield per mother plant, mean crown diameters, and crown and root dry wts were determined. Cultivar effects and cultivar × treatment interactions were not observed, so data for the two cultivars were pooled. Stolon production per mother plant was greatest for trt 1 (18.56 stolons), intermediate for trt 2 (15.75 stolons), and least form 3 (7.89 stolons). For trt 3, crown dieters. and crown and root dry wts were reduced relative to those of trts 1 or 2. Stolons from all trts were planted in a fruit production field on 13 October, 1993. After two months, canopy diameters were greatest for plants from trt 1 (27.1 cm), intermediate for plants from trt 2 (26.2 cm) and least for plants from trt 3 (24.9 cm). The results indicate that, compared to standard soil fumigation with MeBr/chloropicrin. small, but significant, reductions in runner production and plant vigor can be expected following nursery soil fumigation with intermediate rates of chloropicrin.

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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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Douglas V. Shaw and Kirk D. Larson

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).

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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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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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Steven A. Fennimore, Milton J. Haar, Rachael E. Goodhue, and Christopher Q. Winterbottom

runner plant yield results and this article describes weed control results in strawberry nurseries. Some fumigant alternatives to MB currently under investigation are Pic (trichloronitromethane; Niklor Chemical Co., Long Beach, CA), iodomethane (IM