| Rhizobacteria are natural microbial inhabitants associated with plant root zones. Pesticides applied to plants for healthy and economical crops also reach rhizobacteria populations. This can cause shifts in microbial populations, pesticide metabolism, reduced pesticide efficacy, and changes in soil microbial enzymatic processes. The fungicide benomyl has been implicated in reports of plant damage. Rhizobacteria populations have been stimulated and have shown increased phytotoxicity with benomyl application. In this study, Florida soils, cucumber, and marigold plants were treated with drench rates of benomyl. Effects on rhizobacteria populations, soil phosphatase activity, FDA hydrolysis activity, and plant growth were evaluated relative to benomyl application.; Total bacterial populations tended to increase when benomyl was used. Four main phenotypes were found with one identified as Pseudomonas fluorescens which had populations significantly stimulated. Large variations in phosphatase activity were observed over the duration of the experiments. Levels of FDA activity at the end of the study were not significantly different from those at the beginning. Compared to untreated controls, height of treated marigold plants decreased significantly over time by 30%. Marigold shoot weights were 44% of the control over time. Fresh weights of marigold roots decreased by 68% compared to untreated plants. Benomyl residues were highest after the initial treatment, but had a half-life ranging from 10–14 days. Biodegradation by soil microorganisms was likely the major pathway for disappearance of the fungicide as controlled environmental conditions reduced abiotic loss. A slight increase in carbendazim dissipation after the additional application of benomyl suggests enhanced degradation of the chemical. A relationship seems to exist between benomyl degradation (indicated by decreased detection of carbendazim to other metabolites such as benzimidazole) and increases for the Ps. fluorescens suggesting it might be involved in benomyl degradation. |
