Growth and Flowering Responses of Sea Marigold to Daminozide, Paclobutrazol, or Uniconazole Applied as Drenches or Sprays

Borrichia frutescens (L.) DC., sea marigold, is a woody perennial shrub native to the Gulf and Atlantic coasts of North America and has potential as a landscape shrub or groundcover. This study assesses application rates of three commercially available plant growth regulators (PGRs) on B. frutescens during container production. In one experiment, plants were drenched with 0, 0.5, 1, 2, or 4 mg active ingredient (a.i.) pot−1 of uniconazole or 0, 5, 10, 20, or 40 mg a.i. pot−1 of paclobutrazol, and in a second experiment, plants were sprayed with solutions of either 0, 25, 50, 100, or 200 mg a.i. L−1 of uniconazole, 0, 50, 100, 200, or 400 mg a.i. L−1 of paclobutrazol, or 0, 2500, 5000, 10000, or 20000 mg a.i. L−1 of daminozide. Drench-applied paclobutrazol (40 mg a.i. pot−1) reduced shoot mass and root mass (52.9 and 48.5 %, respectively). Both paclobutrazol (40 mg a.i. pot−1) and uniconazole (2 mg a.i. pot−1) reduced leaf number by as much as 56.7 and 23.8 %, respectively. Height was reduced 54.9 % by paclobutrazol at 40 mg a.i. pot−1 and 34.9 % by uniconazole at 2 mg a.i. pot−1. Drench application of paclobutrazol and uniconazole reduced internode extension by 50.1 and 41.4 %, respectively. At the levels tested, daminozide, paclobutrazol, and uniconazole were generally ineffective at controlling growth when applied as a spray. Drench application of paclobutrazol or uniconazole can be used to control height during container production of B. frutescens, whereas spray application rates need to be tested at higher concentrations or multiple applications to achieve desired control.