Effects of Trinexapac-Ethyl On Growth and Development of Three Ornamental Grasses

Ornamental grass sales have drastically increased over the past decade.  As a result, nursery production of grass species has increased to accommodate the increased demand.  In production, ornamental grasses are fast growing which leads to increased space requirements and large quantities of water and fertilizer.  This research evaluated the effects of trinexapac-ethyl (TE), a gibberellin inhibitor, on growth of ornamental grasses. Growth parameters evaluated in this study included plant height, tiller production and chlorophyll content (SPAD) in three ornamental grasses Miscanthus sinensis ‘Variegatus’,  Pennisetum xadvena ‘Rubrum’ and Calamagrostis xacutiflora ‘Karl Foerster’.  Grass plugs were potted in a pine bark medium in 3.8 L containers and topdressed with 15g Osmocote 15-9-12 (Scott’s, Marysville, OH) per container. Plants were irrigated as needed with clear water. Grasses were grown in full sun in Starkville, MS and treated 10 days after planting with 0, 132.4 mg, 220.7 mg, or 308.9 mg TE ·L^-1 with a second application 42 days after initial treatment.  Reduction of plant height was detected in all cultivars evaluated, but the most significant reduction resulted from the second application.  Tiller production in C. xacutiflora ‘Karl Foerster’ decreased with increasing TE rate while M. sinensis ‘Variegatus’ increased tillers with increased TE rate. In C. xacutiflora ‘Karl Foerster’ SPAD readings increased with increasing TE rate.  Although the growth parameter effects were species and cultivar dependent, TE when applied to ornamental grasses has the potential to increase nursery production efficiency by reducing plant growth rates and increasing chlorophyll content.