Height Control of Six Ornamental Grasses with Foliar Sprays of Trinexapac-Ethyl or Uniconazole

The objective of this study was to quantify the influence of foliar sprays of trinexapac-ethyl (TE; Primo Maxx) and uniconazole (Concise) on height control of three ornamental grasses each from Cyperaceae - Carex buchananii, Carex comans ‘Frosted Curls’, and Carex flagellifera ‘Toffee Twist’ and Poaceae - Cortaderia selloana ‘Rosea’, Miscanthus sinensis ‘Gracillimus’, and Muhlenbergia capillaris.  Propagules were transplanted into 13-cm containers and grown in a polycarbonate greenhouse at 25 ± 2.9 °C under natural photoperiods.  Two and 3 weeks from transplanting, grasses from Cyperaceae and Poaceae, respectively received 2 biweekly foliar sprays of TE at 220 mg·L⁻¹ or uniconazole at 20 or 40 mg·L⁻¹.  Spray volume of 1.89 L·m⁻² was applied and a non-sprayed control was maintained.   Ten plants per treatment were arranged in a completely randomized design.  Plant height was recorded 0, 2, 4, and 8 weeks after the initial treatment (WAIT).  Data were analyzed using SAS’s PROC MIXED and pair-wise treatment comparisons were made at p ≤ 0.05.  The mean height of Cyperaceae grasses was not influenced by any treatment in up to 4 WAIT.  In 8 WAIT, the mean height of C. buchananii treated with 20 mg·L⁻¹ uniconazole was suppressed by 16% than controls.  On average, in 8 WAIT ‘Frosted Curls’ treated with 20 and 40 mg·L⁻¹ uniconazole were 13, and 8% shorter than controls, respectively.  In 8 WAIT, mean height of ‘Toffee Twist’ treated with 220 mg·L⁻¹ TE and 20 and 40 mg·L⁻¹ uniconazole was suppressed by 21, 24, and 20%, respectively than controls.  Thus, overall, uniconazole was more effective than TE in controlling height of the Cyperaceae grasses.  The mean height of ‘Rosea’ treated with TE was reduced by 13% than controls in 2 WAIT.  Compared with controls, mean height suppression of ‘Rosea’ treated with TE and 20 and 40 mg·L⁻¹ uniconazole was 23, 15, and 19% in 4 WAIT and 37, 24, and 32% in 8 WAIT, respectively.  Mean height of ‘Gracillimus’ was not influenced by uniconazole in 8 WAIT however; TE suppressed it by 17, 27, and 23% than controls in 2, 4, and 8 WAIT, respectively.  No treatment influenced the mean height of M. capillaris in 2 WAIT.  However, on average, M. capillaris treated with TE was 14 and 35% shorter than controls in 4 and 8 WAIT, respectively.  Thus, overall, TE was the more effective than uniconazole in controlling height of the Poaceae grasses.