Summer-pruning intensity affects on off-season production of primocane-fruiting red raspberries.

Summer pruning of primocane-fruiting red raspberries is an effective technique to induce late season production under non-heated greenhouses in mild-winter climates. The objective of this study was to evaluate the effect of pruning intensity and pruning date on fruit yield. The experiments were carried out in two consecutive years in southern Portugal. In the first year the canes were pruned at 5 to 25 nodes depending on cultivar. The dates where 16, 31 July and 15 August for 'Autumn Bliss','Autumn Cascade' and 'Heritage' respectively. In the second year the canes were pruned at the same number of nodes but on 2, 16 and 30 August. In the first experiment longer pruning gave higher numbers of laterals, higher fruit yield and earliness. The optimal pruning length varied with the cultivar. 'Autumn Bliss' yielded most when pruned at 15 nodes,'Autumn Cascade' at 20 nodes, acid 'Heritage' at 25 nodes. Later pruning in the second year reduced fruit yield without affecting cane growth. Although longer pruning shortened the cropping cycle, pruning early is crucial to avoid yield loss due to the Onset of low-light autumn conditions. Longer pruning induced a higher number of shorter laterals in the three cultivars. This study confirms the possibility of achieving a second crop in November-December when primocanes are cut immediately after the harvest of the normal summer crop.