Primocane blackberry cultivar response to pseudo double-cropping
The recent introduction of primocane-fruiting blackberry cultivars has enabled blackberry (Rubus subgenus Rubus) production in northern climates such as North Dakota. However, primocane yields have been low and methods to increase yield other than tipping, which has been shown to delay fruiting and reduce marketable yield, need to be evaluated. A field study evaluated overwintering primocane sections to determine if pseudo double-cropping of primocane blackberries was possible under North Dakota winter conditions. Four primocane cultivars (Prime-Jan®, Prime-Jim®, Prime-Ark® Freedom, and Prime-Ark® 45) in three growing environments (high tunnel, plastic mulch, and bare soil) were pruned to one of three lengths (0, 15, and 30 cm), before the 2016/17 and 2017/18 winter in order to leave a number of buds for floricane fruiting the following year. Canes were protected with wheat straw and a frost blanket through the winter. Cane dieback and fruit production was recorded and analyzed. Growing environment could not be compared due to the lack of replication. Winter protection did not decrease stem dieback as green stem tissue the following spring was minimal and no visible differences occurred. In 2018, primocane stem retention influenced the number of fruit harvested and the fruit fresh weight on a per plant basis for the months of September and October, along with total fruit number and yield. In October, more fruit was harvested and a greater fresh weight from plants with 15 cm primocane stem retained compared to plants with 30 cm primocane stems retained. For September and total fruit harvested and fresh weight, plants pruned to the soil surface had greater yields compared to plants with 30 cm primocane stems retained. Cultivar influenced monthly and total yield both years with Prime-Jim® and Prime-Jan® being more productive than Prime-Ark® Freedom in 2017, while Prime-Jim® in general was more productive than the other three cultivars in 2018. The season extension capability of a high tunnel environment was observed in 2017 with almost three times more fruit harvested during October in the high tunnel compared to fruit harvested from plants in bare soil or black plastic mulch. A severe storm in June 2018 tore the plastic from the high tunnel frame, thus the late-season ripening that was observed during October 2017, did not occur in 2018. Further research will investigate other thornless primocane cultivars and compare a single poly versus a double poly high tunnel, as well as evaluating additional primocane stem protection for further yield increases.
Hatterman-Valenti, H., Espe, A., Stenger, J. and Auwarter, C. (2020). Primocane blackberry cultivar response to pseudo double-cropping. Acta Hortic. 1277, 293-300
high tunnel, primocane, floricane, blackberry, northern climates