Method to reduce low temperature stress (LTS) in red raspberry ( Rubus idaeus L.)

BACKGROUND: In Nordic regions the floricane of red raspberries often suffer 20-30% injury from exposures to low temperatures. OBJECTIVE: Implemented methods to improve winter survival of red raspberry. METHODS: We studied from 2011 to 2014 the bending and covering effect of red raspberry floricanes of 'Glen Ample', 'Stiora' and selection KV91-39-7 on winter injury and yield. Canes were trained to a rotating cross-arm (RCA) trellis system and covered with two layers of polyethylene (Agricover) sheets, and supplemental heat was provided at critical temperatures. RESULTS: Bending plus heating reduced freezing injury of buds for all cultivars, and tended to increase yield for 'Stiora' and KV91-39-7, but not for 'Glen Ample'. Plots lifted directly to vertical after winter covering yielded more than plots where canes were left horizontal till anthesis and then lifted to vertical. CONCLUSIONS: The experiments show that bending raspberry canes to avoid freezing injury, was possible without much visible cane injury if bending was undertaken carefully using a RCA trellis. However, standard trellising with erect canes improved fruit yield. It was found that a few more cane buds were torn off because of trellising reducing the amount of buds compared to canes in erect position. Additional studies should be undertaken to look at reasons why better cane survival resulted in lower yields.