The fungicide benomyl (formulated as Benlate 50 DF) has been implicated in damage to several crops grown under warm, moist conditions. Although the target pathogen may be controlled, occurrence of population shifts in rhizosphere bacteria has been documented, with benomyl application. A growth chamber study to investigate the effects of benomyl on marigold (Tagetes patula) and subsequent effects on the populations of rhizosphere bacteria of marigold was performed. A one pound per one hundred gallon rate as foliar and drench treatments were applied to marigolds. Plant growth data and rhizosphere bacteria populations were recorded. Repeated application of the benomyl treatments significantly reduced the marigold root and shoot mass, 44% and 67% respectively, compared to controls. Repeated foliar applications of benomyl also resulted in necrotic lesions on marigold leaf margins. Rhizosphere bacteria total numbers differed between treatments, having a greater population for the drench rate than the foliar rate. These results suggest application of benomyl may have harmful nontarget effects, leading to production problems associated with its use.
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