Cyclanilide Increases Branching of Herbaceous Perennials

Many herbaceous perennials would benefit from additional branching to provide fuller pots in shorter production times. Cyclanilide (Tiberon, OHP, Inc., Mainland, PA, USA), a new product recently labeled in the USA for branching of woody ornamentals, was evaluated on several herbaceous perennials over two seasons. Cyclanilide was applied as a foliar spray to established plants grown in 1.1-L pots filled with a peat-lite medium in late summer. Plant height and number of branches were determined at two week intervals after treatment (WAT). Cyclanilide improved the lateral branching of Phlox paniculata ‘Bright Eyes’ with an eight-fold increase in the number of lateral branches per plant at 6 WAT with 20 mg/L (control 2.2 vs. 20 mg/L 17.8 branches). Higher rates of cyclanilide did not further increase the number of lateral shoots but did increase the phytotoxicity symptoms. Echinacea ‘Ruby Star’ treated with 20 mg/L cyclanilide had twice the basal branches as the untreated control. Lateral branching of Coreopsis ‘Sweet Dreams’ was also doubled by treatment with 20 mg/L cyclanilide. However, even 20 mg/L cyclanilide resulted in unacceptable phytotoxicity damage. Therefore, the study was repeated in the spring with lower rates (0, 5, 10, 15, 20, 25, 30 mg/L cyclanilide) applied to three cultivars of Echinacea, ‘Sunrise,’ ‘Sundown’ and ‘Double Decker’, Phlox paniculata ‘Blue Boy’ and Coreopsis ‘Sweet Dreams’. Only Phlox showed a significant improvement in branching for these spring-planted and spring-treated crops. Although cyclanilide may increase branching of some perennials, phytotoxicity may limit its use for spring production, and there are obviously production issues that affect its efficacy. INTRODUCTION Many producers are using a bedding plant production model to fast-track their herbaceous perennials. Many herbaceous perennials branch poorly and therefore could benefit from additional branching to provide fuller pots in shorter production times. Cyclanilide (Tiberon, OHP, Inc., Mainland, PA, USA), a new product recently labeled in the USA for woody ornamentals, increases branching of woody plants (Holland et al., 2007). Cyclanilide has been evaluated on some herbaceous plant material. Although cyclanalide enhanced branching of a poorly branched cultivar of poinsettia (Euphorbia pulcherrima ‘Visions of Grandeur’), phytotoxic damage was unacceptable (Allsup et al., 2007). Treatment of strawflower (Bracteantha bracteata) with cyclanilide increased branching 1.8-fold and caused early phytotoxic damage that was no longer visible at four weeks after treatment (Gu et al., 2007). Our goal was to evaluate cyclanilide on a variety of herbaceous perennials for enhanced branching with limited phytotoxic damage. MATERIALS AND METHODS The same treatment application procedure and experimental design were followed for each trial. After establishment and resumption of growth, about two weeks after potting unless otherwise stated, the plants were treated with a foliar spray of cyclanilide (rates varied with trial) using a hand-held CO2 pressurized sprayer (R&D Sprayers, Inc. Model AS, Opelousas, LA, USA). Sprays were evenly applied over a given time period to Proc. X IS on Flower Bulbs and Herbaceous Perennials Eds.: J.E. van den Ende et al. Acta Hort. 886, ISHS 2011 160 apply 210 ml/m to a square meter area in which five plants of each species were placed. Each plant species was set up as an individual experiment with plants arranged in a completely randomized design with five single plant replications. Data were collected at two-week intervals from four to ten weeks after treatment (WAT) depending on the crop and trial and included plant height (from rim of pot to top of plant, in cm), number of branches and observations of phytotoxicity. Plant height and branching data were subjected to linear and quadratic regression analysis. August 2005 Trial Plugs of Echinacea purpurea ‘Ruby Star’, Phlox paniculata ‘Bright Eyes’, Buddleia × weyeriana ‘Honeycomb’ and Coreopsis rosea ‘Sweet Dreams’ were planted into 1.1-L plastic pots filled with a peat-lite medium (Fafard 52, Conrad Fafard, Inc., Agawam, MA, USA) and irrigated as needed with 200 mg/L N (Peters 20-10-20, The Scotts Co., Marysville, OH, USA). Established plants were treated with a single foliar spray of 0, 20, 40, 60 and 80 mg/L cyclanilide. Data were collected for six weeks. April 2007 Trial A second trial was conducted in the spring using three cultivars of Echinacea, ‘Sunrise’, ‘Sundown’ and ‘Doubledecker’, Coreopsis rosea ‘Sweet Dreams’ and Phlox paniculata ‘Blue Boy’ plugs planted in 1.1-L plastic pots filled with a peat-pine bark medium (Fafard 3B, Conrad Fafard, Inc.). Plants were fertilized as above and allowed to establish and resume active growth after transplanting (about two weeks after potting) before cyclanilide was applied as described above at 0, 5, 10, 15, 20, 25 or 30 mg/L. Plants were measured at 2 and 4 WAT. RESULTS AND DISCUSSION August 2005 Trial Echinacea purpurea ‘Ruby Star’ showed an immediate response to cyclanilide with a significant quadratic increase in the number of basal branches ≥2 WAT (Fig. 1). There was no additional increase in the number of branches with rates above 20 mg/L. In fact, increased phytotoxicity at the higher rates tended to decrease growth and therefore, branching. The phytotoxicity was evident at five days after treatment as distorted foliage. Crinkling and cupping of the foliage was still obvious at later evaluations with the higher rates of cyclanilide. Cyclanalide had no significant effect on plant height. Phlox paniculata ‘Bright Eyes’ also showed rapid response to cyclanilide treatment with nearly a five-fold increase in the number of branches at 2 WAT with a 20 mg/L treatment (Fig. 1). Again increasing rates above 20 mg/L did not increase branch numbers significantly. Cyclanilide did not affect the number of shoots arising in the pots. Again, phytotoxicity was obvious at nine days after treatment and persisted especially at higher rates. Cyclanalide had no significant effect on plant height. Buddleia × weyeriana ‘Honeycomb’ was less responsive to cyclanilide than the other cultivars but rates at or above 40 mg/L increased branch numbers at 2 WAT but the significance of the response did not persist (Fig. 1). There was little evidence of phytotoxicity on the Buddleia. Coreopsis rosea ‘Sweet Dreams’ was very responsive to cyclanilide with increased branching at rates of ≥20 mg/L at 4 WAT (Fig. 2). The large number of branches made this plant very difficult to evaluate. Therefore, only 2 and 4 WAT were taken. Coreopsis showed less phytotoxicity than the other crops. All four crops responded to low rates of cyclanilide by increased production of lateral shoots (not increased number of basal shoots except for Echinacea). Phytotoxicity increased with increasing rates. April 2007 Trial Of the five crops tested in the Spring 2007 trial, only Phlox ‘Blue Boy’ showed a