Growth Retardant Application to Canna × generalis ‘Florence Vaughan’

Abstract

Abstract The effects of 15 to 45 ppm Cutless (flurprimidol), 2500/1500 to 7500/1500 ppm B-Nine/Cycocel tank mixes (daminozide/chlormequatchloride), and 20 to 60 ppm Sumagic (uniconazole) on the vegetative growth and flowering of Canna x generalis ‘Florence Vaughan’ were determined during container nursery production and landscape establishment. Vegetative heights 30 and 60 days after treatment (DAT) and vegetative and inflorescence heights at first and second flower were suppressed by all plant growth retardants (PGRs). There was no delay in flowering of the first inflorescence from any PGR treatment, and a three to seven day delay in flowering of the second inflorescence with only Sumagic. Vegetative height was suppressed quadratically 14–28% (30 DAT) and linearly 19–40% (60 DAT) by increasing Cutless rates. Inflorescence heights of plants treated with 15 or 30 ppm Cutless were suppressed proportionally to foliage heights without any detrimental effect on floral display. Heights of plants treated with Cutless and transplanted into the landscape at 60 DAT were similar to those remaining in containers at 90 DAT, and 7 cm (3 in) and 11 cm (3.5 in) taller at 120 and 150 DAT, respectively. Vegetative heights of plants in both locations were suppressed linearly by Cutless, 15–33% (90 DAT) and 7–12% (120 DAT) with height suppression effects dissipating by 150 DAT. Vegetative height was suppressed quadratically by B-Nine/Cycocel, 5–14% and 16–28% at 30 and 60 DAT, respectively. However, response was inconsistent with rate at all sampling dates both in containers and in the landscape. B-Nine/Cycocel treated plants were suppressed quadratically up to 33% (90 DAT) and up to 17% (120 DAT). Plants transplanted and treated with B-Nine/Cycocel were suppressed linearly 14–23% (90 DAT) and 6–16% (120 DAT). At 150 DAT, BNine/Cycocel treated plants were similar in height to control plants, with transplanted plants around 10 cm (4 in) taller than those remaining in containers. Sumagic suppressed vegetative height quadratically 28–33% (30 DAT) and 50–52% (60 DAT). At 60 DAT, the height suppression was excessive and leaf orientation was altered to a less upright position. Inflorescence height suppression by Sumagic was considered excessive with first and second flower occurring below the surrounding foliage. Compared to those transplanted into the landscape at 60 DAT, plants treated with Sumagic and remaining in containers were 12% (90 DAT), 36% (120 DAT), and 37% (150 DAT) shorter. In both locations, Sumagic suppressed vegetative height quadratically 46% (90 DAT) and 29% (120 DAT) compared to control plants. Compared to control plants, at 150 DAT, treated plants remaining in containers were suppressed to a greater extent (32–43%) than those transplanted into the landscape (11–14%).