Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: September 1, 2009
Publication Date: November 10, 2009
Citation: Hanson, B. D., Gerik, J. S., and Schneider, S. M. 2009. Weed and pathogen control with reduced methyl bromide rates in open-field nurseries. Page 97 in: Proc Annu. Intl. Res. Conf. Methyl Bromide Alternatives Emissions Reductions. Interpretive Summary: In order for perennial crop nursery stock to certified as nematode-free, California nursery operations rely on preplant soil fumigation with methyl bromide or 1,3-dichloropropene. Methyl bromide is being phased out because of its potential to deplete stratospheric ozone depletion and is only used where critical needs exist. However, current use rate recommendations by the international technical committee are much lower than rates required by California nursery certifications regulations. This research was conducted to test the efficacy of reduced rate methyl bromide applications in California nursery production systems. Reduced methyl bromide rates controlled pests as well as the industry standard treatment in these trials; however, it is possible that long-term use of reduced rates may have different results than in these single nursery cycle experiments.
Technical Abstract: Producers of nursery stock in California rely on preplant soil fumigation to meet requirements for nematode free planting stock. Certified clean stock is essential for successful establishment and future productivity of new orchards and vineyards and is a requirement for intra- and interstate as well as international commerce of planting materials. Methyl bromide is the most commonly used fumigants in tree and garden rose nurseries; however, this chemical is being phased out because of its effect on stratospheric ozone. Methyl bromide is still used in nursery crops under the Critical Use Exemption provisions of the Montreal Protocol. Methyl bromide available for for critical uses has decreased because new calculations used by the Methyl Bromide Technical Options Committee (MBTOC) for calculating industry allotments are based on "standard presumptions" for efficacious rates below those currently used in California nurseries. The current research project was undertaken to test the efficacy of MBTOC standard presumptions under local growing conditions and compare reduced rate MB applications under low permeability barrier films to standard application rates. The results of two trials in commercial nurseries were favorable; however, it is possible that long-term use of reduced rates may reveal weaknesses not evident in single-cycle field experiments. Additionally, full- and reduced-rate methyl bromide treatments tended to provide more complete and consistent control of nematode and weeds pests compared to the alternative fumigant, 1,3-dichloropropene in these trials.