In one experiment conducted in 1998 and two in 1999, Coreopsis rosea ‘American Dream’, or pink coreopsis, were treated with four plant growth retardants (PGRs): B-Nine from 2500 to 7,500 ppm, Cutless from 25 to 150 ppm, Sumagic from 10 to 40 ppm, and Bonzi from 25 to 100 ppm. The study was conducted to determine whether PGRs could be used to suppress growth of pink coreopsis without delaying flowering or causing phytotoxicity. Application of B-Nine, Cutless, or Sumagic suppressed plant growth 13–31% at first flower and when plants were marketable (one-third of flowers open) in all experiments and improved plant quality compared to controls. Plants treated with B-Nine, Cutless, or Sumagic had quality ratings 52–67% higher than those of control plants when marketable; treated plants appeared denser and more floriferous. Time to first flower and to a marketable stage were minimally affected by PGR application, and no phytotoxicity was observed. Bonzi did not significantly control growth or affect flowering of pink coreopsis in any of the three experiments.

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Author notes

2Graduate student.

3Professor.

4Assistant Professor.