Growth Control of 'Glen Ample' and 'Tulameen' Raspberry Cultivars with Single and Repeated ProCa Applications

Prohexadione-calcium (ProCa) is used to control vegetative growth in some fruit crops. We evaluated the effects of single and repeated ProCa treatments (100 or 200 ppm) on vegetative growth and cropping potential of biennial-fruiting raspberry (Rubus idaeus L.) cultivars 'Glen Ample' and Tulameen'. After the initial reduction in primocane growth rate, growth resumed three to four weeks after the first ProCa application. The second application was necessary to achieve permanent reduction in cane height. In 'Glen Ample', primocane growth was reduced by 25 to 28 cm and dry weight by 18 to 26 % following two ProCa treatments. In 'Tulameen' the reduction in primocane growth was 15 cm, and in cane dry weight 19 %, when treated twice with 200 ppm ProCa. After ProCa applications, treated plants produced shorter internodes than the control plants. However, after growth resumption new internodes in the treated plants were longer than in the control plants. Effects on the reproductive performance were evaluated after dormancy release. In 'Glen Ample', repeated ProCa applications reduced the number of lateral shoots, as well as the number and proportion of flower buds, and slightly delayed flowering. Presumably, altered gibberellic acid metabolism had interfered with flower induction. However, the total number of flowers per cane was not affected in either of the cultivars. As ProCa was effective in reducing vegetative growth of primocanes without affecting cropping potential, it may become useful in growth control of biennial fruiting raspberry cultivars. However, timing and number of ProCa applications are extremely crucial.