Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 8/19/1998
Publication Date: N/A
Technical Abstract: Horticulture production worldwide uses various pesticides to control pathogens and insure a quality, economical crop including benomyl [Methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate], a systemic fungicide for control of many fungal plant pathogens on ornamental and edible crops. Pesticide application normally controls the target pest. However, nontarget organisms may populate the treated area including bacteria inhabiting the rhizosphere, known as rhizobacteria. Without the natural competition from fungi inhabiting the rhizosphere, the rhizobacteria may flourish. Additionally, the pesticide may stimulate the rhizobacteria populations directly as an energy source. The objective of the research reported in this paper was to determine the effects of benomyl on growth and phytotoxicity of rhizobacteria developing in the rhizospheres of horticultural crops. Plant rhizosphere and soil samples from production fields treated with benomyl were screened for bacterial populations on King's B agar. The populations enumerated were typically higher for treated soils and plants than for untreated ones. Soil bacterial populations increased more than fourfold when treated with benomyl. Soils with histories of pesticide application exhibited populations of microorganisms acclimated to the pesticide. Bioassays using lettuce (Lactuca sativa ) seedlings were performed to assess phytotoxicity. Typically, more than 50% of rhizobacteria screened from benomyl-treated soils exhibited significant phytotoxicity. Results indicate that repeated applications of pesticides may indirectly have a negative effect on nontarget organisms by enhancing phytotoxicity toward desirable plants.