2008 Annual Report
1a.Objectives (from AD-416)
Collaborate in conducting raised-bed, plastic covered field-plot experiments designed to enhance dispersion and efficacy of low-vapor-pressure alternative fumigants (including 1,3-dichloropropene and chloropicrin) compared to methyl bromide for control of nematodes, pathogens, and weeds in Florida soils used for vegetable production, while improving retention of fumigants in the target treatment zones with virtually impermeable films and other materials between soil beds.
1b.Approach (from AD-416)
Laboratory and field experiments will be conducted to determine the feasibility of using carbonated water to function as a propellant for enhancing the dispersion of low- vapor-pressure fumigants such as Telone InLine (a mixture of 1,3-dichloropropene and chloropicrin) applied via irrigation drip tubes under plastic covered beds. A pinpoint carbonator will be employed to carbonate the irrigation water before the fumigant is injected into the drip tube delivery system. A three dimensional array of soil sampling probes will be used to sample soil-pore air-space concentrations to determine the effectiveness of the dispersion enhancement system. Effectiveness of dispersion will be compared with measured concentration distributions of noncarbonated delivery applications of the low-vapor-pressure fumigant, as well as compared with measured concentration distributions of methyl bromide itself. Various techniques will be applied to reduce emissions from the bedded rows and middles to the atmosphere.
This project is related to both objectives of this inhouse project: objective 1: Improve efficacy of low-vapor-pressure alternative pre-plant soil fumigants, such as 1,3-dichloroporopene (1,3-D), chloropicrin (CP), and metam sodium/methyl isothicocyanate (MITC), by improving dispersion and distribution in the target treatment zone by use of carbonated solutions that degas within the soil and thereby propel the dispersion of fumigant vapors and objective 2: Improve retention of soil fumigants by improved placement of virtually impermeable plastic films, especially in the middles between raised-bed plasticulture systems by deeper placement of the film along the row sides.
Cooperators progress report. The goal is to increase the efficacy of the alternative fumigant, Telone C35 (1,3-dichloropropene plus 35% chloropicrin), in comparison to methyl bromide. An alternative system being tested is using wavelength selective plastic mulches with carbon dioxide (CO2)-propelled Telone C35. These mulches control nutsedges by allowing infra-red and red light to penetrate while restricting other wavelengths. Infra-red and red light change the morphology of emerging nutsedge from a hard point to a soft leafy structure that cannot tear the film. The rationale is that the greater efficiency of methyl bromide is due to its high vapor pressure allowing it to disperse rapidly through soil. Increasing transport of Telone C35 can be accomplished by pressurizing with CO2. Carbonation of the fumigant can occur by saturating Telone products with CO2 at a pressure well above ambient. Upon injection, the degassing CO2 should sweep the fumigant vapors through the soil. This process should allow Telone C35 to achieve a faster and more even distribution like methyl bromide, and create a much larger “killing zone” in a shorter time. The use of a carbonated fumigant with appropriate mulch film technology may be a low cost alternative to methyl bromide. General conclusions are: (1) Nutsedge control by wavelength selective film was better than for black virtually impermeable film (VIF), if no fumigant was used. Statistically, metallic polyethylene film (PE) and black VIF with Telone C35 controlled weeds as well as wavelength selective films, although crop yield was best for metallic PE mulch; (2) The use of CO2 with Telone C35 caused quicker, deeper distribution of the fumigant than when dispensed by nitrogen (N2) (3) Although carbonated Telone C35 achieved greater distribution, the rate of disappearance from the soil was not shortened much; (4) Volatilization from the bed was increased by use of CO2 compared to beds applied with N2 for comparable rates of Telone C35.
Monitoring Activities. Field project plans, accomplishments and poster presentations were reviewed by email exchanges. Calibration of fumigant injection equipment was discussed and resolved. Field plot site visits were conducted several times during the soil preparation and fumigation stages, and during the actual vegetable production season.
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