Fourteen herbicides or herbicide combinations, a wood chip mulch, a chipped rubber tire mulch, and a newspaper mulch were evaluated for weed control efficacy and potential phytotoxicity using 12 species of herbaceous perennials under field-growing conditions. Nineteen herbicides or herbicide combinations were similarly evaluated under container-growing conditions using 11 species of herbaceous perennials. The effect of herbicide application time also was monitored through application of herbicides to dormant and actively growing plants. Herbicides and mulch treatments were compared to weeded and nonweeded controls. Herbicide phytotoxicity effects were dependent on the age and species of the herbaceous perennial and herbicide application timing. Herbicide injury was generally greater for newly established plants compared to established plants. Although injury was usually reduced when herbicides were applied to dormant plants, injury was sometimes greater when herbicides were applied in early spring compared to applications made in late spring after complete herbaceous perennial emergence. This effect resulted in injury to young shoots that had emerged before the earliest possible time that herbicides could be applied in early spring. A wood chip mulch provided the most effective weed control and highest quality plants under field growing conditions. Several of the herbicides evaluated demonstrated potential for weed control in both field and container herbaceous perennial production systems and landscape plantings.
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