Screening Perennial Bedding Plants for Response to Plant Growth Regulators
Perennial bedding plant species were tested for response to single treatments of Sumagic (0, 15, 30, 45, or 60 ppm), Bonzi (0, 40, 80, 120, or 160 ppm), Cycocel (0, 750, 1500, 2250, or 3000 ppm) or B-Nine (5000 ppm, applied twice) applied during greenhouse production in Spring 1997. Plant height of both Chrysanthemum parthenium and Malva alcea had a quadratic response to Sumagic and Bonzi rates, with excessive height reductions at the lowest application rates at 4 weeks after treatment. All rates of Cycocel reduced plant height of C. parthenium and M. alcea by 33% and 40%, respectively. These species did not establish in the landscape. Verbena bonariensis was moderately responsive to Sumagic and Bonzi, but not Cycocel. Application rates of 15 and 30 ppm Sumagic or 160 ppm Bonzi provided moderate height control without landscape persistence beyond 4 weeks after planting. Leucanthemum × superbum `Alaska' was responsive to Sumagic and Bonzi, but not Cycocel or B-Nine. Rates of 15 ppm Sumagic or 40 ppm Bonzi provided moderate control without landscape persistence. Plant height of Monarda didyma `Blue Stocking' had a linear response to Sumagic and Bonzi rates. Plant height of Rudbeckia fulgida var. Sullivantii `Goldstrum' was reduced by Bonzi and Sumagic but not B-Nine or Cycocel, with recommended rates of 30 to 40 ppm Sumagic or 160 ppm Bonzi. Treatment of Sedum × `Autumn Joy' with Sumagic resulted in excessive landscape persistence of growth retardation at all rates, but Sedum was not responsive to Cycocel. Veronica alpina `Sunny Border Blue' was responsive to all rates of Cycocel, but growth retardation persisted through 12 weeks after planting.