Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: September 1, 2008
Publication Date: November 6, 2008
Citation: Gerik, J. S., and Wang, D. 2008. Dose response of Agrobacterium tumefaciens to soil fumigants. Page 110 in: Proc Annu. Intl. Res. Conf. Methyl Bromide Alternatives Emissions Reductions. Interpretive Summary: Cut flower growers in California have routinely used methyl bromide with and without chloropicrin for pre-plant soil fumigation to control soilborne pathogens and weeds. Methyl bromide depletes the ozone layer in the upped atmosphere and it use has been severely curtailed since 2005. Alternative treatments are needed to control soilborne pathogen and weeds. The effectiveness of acrolein, vapam, InLine and chloropicrin to reduce populations of the crown call pathogen was studied in the laboratory. Dose response curves were generated from a logistic regression model, and the effective doses to reduce the pathogen population by 50% and 90% were calculated for each chemical. The pathogen was most susceptible to acrolein, followed by vapam, inline and chloropicrin in that order. Effective treatments using acrolein could be developed if the cost of the treatment is economically feasible.
Technical Abstract: Cut flower growers in California have routinely used methyl bromide with and without chloropicrin for pre-plant soil fumigation for the control of soilborne pathogens and weeds. Recent research to identify alternatives to methyl bromide for flower growers has involved combinations of 1,3-dichloropropene, chloropicrin, and metam sodium. Recently other emerging alternative chemicals have been proposed as replacements for methyl bromide; one of these is acrolein (2-propenal; Baker Petrolite Inc. Bakersfield, CA). Acrolein has been formulated and registered for use as an aquatic herbicide in irrigation systems. It also is used to control microorganisms and bacteria in oil wells, liquid hydrocarbon fuels, cooling-water towers and water treatment ponds. We report on the efficacy of acrolein compared to other soil fumigants to control Agrobacterium tumefaciens in soil. The chemicals were applied to field soil in plastic tubes in a manned to simulate a field application made by drip irrigation. Post treatment populations of the pathogen were determined by dilution plating on a selective medium. The population of A. tumefaciens in the treated soil was related to the chemical dose by the following model: Y = Y0 + a / 1 + e ((X – X0) • b), where Y is the population and X is the log of the chemical dose. LC50 and LC90 values were computed from the predictive values of the regression. The acrolein, metam sodium, and InLine treatments did fit the model; even though the R2 values were low, they were significant (P <0.05). Metam sodium had the lowest LC50, but acrolein had the lowest LC90 and the largest slope at the inflection point of the curve indicating greater susceptibility of the pathogen to this treatment. The susceptibility of the pathogen to Inline was found to be quite low. The data for the chloropicrin treatment did not fit the model and this treatment is no longer considered here. The conclusion from this study is that acrolein could be a feasible treatment to control crown gall; however, the feasibility will depend on the cost of the treatment.