A comparison of the effects of a new quaternary ammonium growth retardant with those of other growth retarding chemicals on the pot chrysanthemum (Chrysanthemum morifolium)

Abstract

SUMMARY A new quaternary ammonium growth retardant, i‐allyl‐i‐(3,7‐dimethyl‐octyl)‐piperidinium bromide (ADOPB), was compared with daminozide, ancymidol and chlorphonium chloride for its effectiveness in reducing lateral stem length in the pot chrysanthemum (Chrysanthemum morifolium). Single foliar sprays of ADOPB applied at 100 to 250 ppm active ingredient (a.i.) gave excellent height control without phytotoxicity in cv. Bright Golden Anne throughout the year. Similar results were obtained in two trials with cvs Purple Anne and Regal Anne. As much as 10 to 50 times this concentration of daminozide was required to achieve a similar degree of height control. However, under summer conditions even high concentrations of daminozide did not adequately reduce stem length. Foliar sprays of ancymidol (50–100 ppm a.i.) also gave good control of stem length but this chemical was more effective when applied as a compost drench. Compost drenches of ADOPB reduced stem extension but a greater quantity of a.i. was required compared to a foliar spray. Foliar sprays of dikegulac‐sodium (100 to 5000 ppm a.i.) were very phytotoxic. Reductions in thelength of lateral stems were associated with marked decreases in their fresh and dry weights. Growth retardants delay the flowering of pot chrysanthemums by inducing a slower rate of flower bud development. Foliar sprays of ADOPB generally delayed flowering by 2–3 days more than did sprays of daminozide, but this was comparable with that associated with the use of compost drenches of chlorphonium chloride. High concentrations of all the retardants reduced the diameter of open flowers. Only daminozide caused a loss of flower colour in cv. Regal Anne. The results are discussed in relation to the mode of action of growth retardants, with particular reference to the effects of gibberellins on stem extension and flower development in the chrysanthemum.