CHEMICAL CONTROL OF SUGARCANE VERTICAL GROWTH TO IMPROVE THE QUALITY OF SEED CANE

THE GIBBERELLIN inhibitors, paclobutrazol (Cultar!) and trinexapac-ethyl (MODDUS!) were applied to sugarcane that was grown for use as seed cane. The aim of the treatments was to restrict vertical growth of the sugarcane to reduce the risk of lodging and to shorten the distance between nodes. Erect sugarcane with short internode distance is ideal for planting through billet planters. Paclobutrazol at rates of 1.25, 2.5 and 3.75 kg active/ha restricted growth by 26% for four weeks, 31% for seven weeks and 66% for seven weeks, respectively, in the cultivar Q181A. Repeat treatments two months after the initial treatment generally had a greater effect than the initial treatment. Paclobutrazol caused no deleterious symptoms other than restricted growth at rates up to 10 kg active/ha in cultivar Q158. In both cultivars, the internode length was restricted significantly, but the chemical had no deleterious effect on germination of billets taken from the treated cane. There was a slight stimulation of early germination in paclobutrazol-treated billets but, at the end of the germination period, there was no difference between treatments. Paclobutrazol may be a useful treatment in the management of sugarcane nursery plots. Trinexapac-ethyl also restricted vertical growth at rates of 25 g/ha and above. Unfortunately, the duration of the growth restriction could not be measured in this experiment because of lodging in the field. Trinexapac-ethyl did not affect germination of the treated cane but it caused a stunting of the germinating shoots at higher rates. The chemical was still active in the plant 11 and 16 weeks after treatment, and the vertical growth of the germinating shoots was restricted for 6-8 weeks after germination compared to the untreated control.