Pruning severity affects yield, berry weight, and hand harvest efficiency of highbush blueberry

The following pruning treatments were studied in mature 'Bluecrop' (1996-2000) and 'Berkeley' (1996-98) plants: 1) "conventional" pruning with removal of unproductive canes, thinning of 1-year-old shoots at the base of the bush, and removal of any unproductive wood or thinning of excessive fruiting wood near the top of the bush, as required; 2) "speed" pruning involving removal of one or two of the most unproductive canes at the base of the bush; and 3) "un-pruned" where no pruning was done for the length of this study. Conventional pruning took an average of 6.4 min/plot, while speed pruning saved 88.8% time. There was no pruning treatment effect on the percentage of fruit buds in 'Berkeley' (42%) or 'Bluecrop' (34%) or percent fruit set (70% to 90%, depending on cultivar and year) in any year. Un-pruned plants of both cultivars had significantly greater yield than conventionally pruned plants, depending on the year, while speed pruning generally resulted in intermediate yields. Un-pruned and speed-pruned plants produced berries that were 19% to 27% smaller than conventionally pruned plants, depending on year. The fruit harvest season of un-pruned plants began 3 to 5 days later and lasted a week longer than that of conventionally pruned plants. The harvest efficiency of un-pruned plants was reduced as much as 51% in the later years of this study and was most closely correlated with berry weight. Conventionally pruned plants had a significantly higher percentage of the above-ground dry weight allocated to 1-year-old wood and crown than un-pruned plants. In 'Bluecrop', N concentration tended to be higher in the crown of conventionally pruned plants than in un-pruned or speed-pruned plants. Conventionally pruned 'Bluecrop' plants had significantly higher concentrations of K and P and lower N than un-pruned plants and 'Berkeley' had lower concentrations of N, than un-pruned plants. Results indicate that not pruning mature plants may be an option in the short-term, but may have undesirable effects for long-term sustainability.