Chemical control of shoot growth and axillary inflorescence development in Chrysanthemum morifolium Ramat with 2,3-dihydro-5,6-diphenyl-1,4-oxathiin

Summary

A substituted oxathiin (code name UBI-P293) was wholly effective as a growth retardant on pot-grown Chrysanthemum morifolium ‘Bright Golden Anne’, a tall cultivar, in a single foliar spray at concentrations up to 2 000 mg a.i.l^-1. The application must be made at a later stage of growth than is normally recommended for daminozide; the delays in flowering were similar to those recorded for daminozide, i.e., less than with chlorphonium chloride or piproctanyl bromide. Unlike daminozide, UBI-P293 did not appear to change flower colour in a dark pink cv, Regal Anne. At higher levels the compound induced further decreases in stem extension and also inhibited the development of 50% or more of the axillary inflorescences, though the need for manual disbudding was not entirely eliminated. In order to achieve both height control and a substantial disbudding effect in one operation the concentration of the foliar spray and the timing of its application were critical. Too high a concentration at an ‘early’ stage of growth of the lateral shoots not only induced unnecessarily short stems but also severely retarded the development of terminal inflorescences and caused undesirable mottling and paling of young leaves on the lateral stems. When a substantial disbudding effect was realized the delays in flowering were similar to those expected for piproctanyl bromide.