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One of the proposed alternative chemicals for methyl bromide is 1,3-D. The most common forms of 1,3-D products are cisor trans-isomers of 1,3-D with the fungicidal agent, chloropicrin, containing such mixtures as 65% 1,3-D and 35% chloropicrin (C-35). Soil fumigants are commonly applied under a polyethylene film in Florida raised bed vegetable production. Much of the research regarding cropping system effects of alternative fumigants to methyl bromide has focused primarily on plant growth parameters, with little regard to the atmospheric fate of these chemicals. The objective of this research was to determine both the atmospheric emission of 1,3-D under different plastic film treatments and to evaluate effects of application rates of 1,3-D and C-35 on plant pests, growth, and yield of Sunex 9602 summer squash (Cucurbita pepo L.). Results showed that use of a high barrier polyethylene film (or virtually impermeable film VIF) greatly reduced fumigant emission compared to ground cover with conventional polyethylene films or uncovered soil. Summer squash seedling survival was a severe problem in several of the 1,3-D alone treatments where no fungicidal agent was added, whereas C-35 resulted in excellent disease control at both full and one-half of the recommended application rates for this chemical. Both 1,3-D and C-35 provided good plant stands and higher yields when applied at their recommended application rates. However, all squash yields were lower than typical squash production levels due to late planting and early winter frost kill. Chemical names used: 1,3-dichloropropene (1,3-D); trichloronitropropene (chloropicrin). fumigant use in the United States by the year 2005 due to its potential to deplete atmospheric ozone (USDA, 1999). An alternative compound, 1,3-D, is of importance because it is currently the foremost chemical replacement for MeBr (Locascio, et al., 1997; Schneider, et al., 1995). Although 1,3-D based compounds are not ozonedepleting, they are classified as toxic air substances due to their adverse toxicological effects as determined by the U.S. Environmental Protection Agency’s Clean Air Act (USEPA, 1993). The demand for 1,3-D to replace MeBr, and the little time to properly study what influences 1,3-D and 1,3-D mixtures with 35% chloropicrin (C-35), will have on crop development, pest/pathogen management, and the environment make it imperative that studies regarding 1,3-D touch upon all these concerns. Of particular concern is the efficacy of 1,3-D based pesticides in controlling fungal diseases due to a long history of seedlings succumbing to these pathogens shortly after germination and emergence (Mitchell and Rayside, 1986). Much of the crop research performed on sandy soils does not address the impact of early fungal disease problems (Noling and Becker, 1994), such as seedling survival and damping Received for publication 23 June 2000. Accepted for publication 12 Mar. 2001. Florida Agricultural Experiment Station journal series R-07724. We thank Arthur Hornsby and John Thomas of the Dept. of Soil and Water Sciences, Univ. of Florida, Gainesville, for lending equipment necessary for collection of volatile gas samples. We also thank Wayne Wynn, Andy Frenock, Mike Alligood, and Tom Hewlett, U.S. Department of Agriculture, Agricultural Research Service (USDA/ARS) and Univ. of Florida employees, for technical assistance. We express gratitude to Jim Ralles (San Francisco, Calif.) and Klerk’s Plastics (Hoogstraten, Belgium) for generous donation of Hytibar film. Mention of trade names or proprietary products is for the convenience of the reader only, and does not constitute endorsement or preferential treatment by USDA/ARS or the Univ. of Florida. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Present address: U.S. Department of Agriculture, Agricultural Research Service, Water Management Research Laboratory, 2021 S. Peach Ave., Fresno, CA 93727; e-mail shadnelson@usa.net. Corresponding author; e-mail lhajr@gnv.ifas.ufl.edu. The soil fumigant methyl bromide (MeBr) has been implicated as an ozone-depleting agent (Yagi et al., 1995; Yung, et al., 1980). MeBr is scheduled to be phased out of production for agricultural off. This, in turn, can lead to lack of important information when evaluating a chemical’s potential efficacy for adequately replacing other chemicals when dead seedlings are replaced by new seedlings or reseeded. It has been reported that conventionally used polyethylene films are, in fact, permeable to MeBr (Yates, et al., 1996b). This poses a serious concern for long-term use of alternative soil fumigants, since lack of volatilization control after application may lead to atmospheric contamination and severe use restrictions. Use of alternative polyethylene films with much lower permeability than conventional polyethylene films may provide the means for retaining soil fumigants within the soil (Gamliel, et al., 1998; Wang and Yates, 1998). These film products are called virtually impermeable films (VIF), because they are only slightly permeable to soil fumigant gases. It has also been suggested that the amount of chemical needed for application may be reduced by as much as one-half because of the increased retention of the chemical within the soil by the VIF (Wang, et al., 1997). A large portion of research regarding MeBr and 1,3-D has been conducted in laboratories to determine quantitatively the volatility of each compound and how to improve agricultural management practices to reduce atmospheric emission of these compounds (Gan, et al., 1998b; Trout and Ajwa, 1998). Although the vapor pressures of 1,3-D isomers are much lower than that of MeBr (34.3 and 23.0 mm Hg for cisand trans-1,3-D at 20 °C), they are still sufficiently high to result in significant atmospheric emissions (Gan et al., 1998a). Few studies have been performed regarding the fate of 1,3D in large-scale field studies to simulate an agricultural production scenario. Therefore, the objectives of this study were to 1) determine volatility of 1,3-D from bare, nontarped beds, and from VIF and polyethylene tarped beds, 2) evaluate efficacy of 1,3-D based compounds to control soilborne pests/pathogens, and 3) collect yield data on summer squash (Cucurbita pepo) to adequately describe the value of different chemical and film treatments. Materials and Methods FIELD SITE AND MEASUREMENT OF VOLATILIZATION. A field site consisting of Arredondo fine sand (loamy, siliceous, hyperthermic, Grossarenic Paleudult), a course-textured soil of low organic matter content (≈1.0%), located at the Institute of Food and Agricultural Sciences’ Green Acres research farm near Gainesville, Fla., was selected for the study. In the past, this field site had been cultivated repeatedly under spring and fall plantings of tomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativus L.), and squash for studies involving crop production alternatives to MeBr. The field site was prepared 9 Sept. 1999 by tilling the soil and 0.9-m wide, 0.15-m high beds were shaped into rows that were spaced 1.8 m apart on center. Beds were then fertilized using a drop spreader by applying 10N–4.4P–8.3K granular fertilizer at a rate of 800 kg·ha and rototilling it into the top 0.3 m of the bed. Later, N at 16.5 kg·ha in the form of NH4NO3 and K at 16.5 kg·ha in the form of KCl was added six times in weekly applications through drip irrigation beginning 1 Oct. Calcium (in the form of CaO) at the rate of 1.17 L·ha was applied weekly beginning at flowering to reduce the incidence of blossom-end rot. Double-wall drip tubing (Chapin Twinwall, Watertown, N.Y.) with emitters spaced 0.3 m apart and a flow rate of 62 mL·min per 30.5 m of row was placed about 0.1 m from the plant stems for application of water, fertilizer, and Ca. One honeybee (Apis nellifera L.) hive per 2.5 ha was placed near the fields at flowering to aid pollination (Hochmuth et al., 1998). The field layout consisted of a randomized complete block design consigned to six blocks with fifteen 12-m length beds in each plot. Outer rows were left untreated and served as buffer rows and the inner rows consisted of 13 completely randomized treatments. The 13 treatments consisted of different film, fumigant, and chemical rate treatments. The film treatments included 1) a white over black (white/black) 0.025-mm (1-mil) thick polyethylene plastic film, 2) a clear, 0.025-mm thick, Hytibar (Klerk’s Plastics, Hoogstraten, Belgium) high barrier VIF, and 3) beds without polyethylene film (no film). The fumigants consisted of three treatments: 1) 1,3-D, 2) 1,3-D with 35% chloropicrin (C-35), where chloropicrin is added as a antifungal agent, and 3) no fumigation. Fig. 1. Portable above ground, polypropolene plastic air sampling chamber. Internal air and thermocouple shafts extended 0.1 m within the chamber to the approximate center for more accurate sample collection and readings from the external sampling ports. The open end of the chamber was placed on the plastic or bare soil and sealed around the edges by a weight on top of the chamber or with tape as appropriate to minimize wind disruption. Gas samples were withdrawn using a 50-mL syringe to collect 1,3-dichloropropene on ORBO-32 charcoal tubes. The chemicals were consigned to three rates, full, one-half, and zero of the manufacturers recommended application rates. The C-35 chemical rate treatments were adjusted so that an equivalent amount of 1,3-D was applied to full and one-half rate treated rows of both 1,3-D and C-35 plots. The following film, fumigant, and chemical rate treatments were made: three check treatments-film = no film, white/black, and VIF, fumigant = none; two treatmentsfilm = no film, fumigant = 1,3-D, rates = full and one-half; two treatmentsfilm = white/black, fumigant = 1,3-D, rates = full

Volatilization of 1,3-Dichloropropene in Florida Plasticulture and Effects on Fall Squash Production