The 2011 ASHS Annual Conference

Commercial orchards of ‘French’ prune (Prunus domestica) in California are typically hand pruned using lopers and ladders -- the most expensive on-farm activity of the season for growers.  However, recent studies conducted in the northern Sacramento Valley suggest that mechanical pruning techniques, in combination with less-detailed hand-pruning from the ground, may reduce pruning costs without adversely affecting yield or fruit size. In 2010, a study was conducted in the southern San Joaquin Valley to determine the impact of mechanical pruning on tree height, canopy light interception, yield and fruit size.  In February 2010, four pruning techniques (standard hand prune with lopers and ladders, mechanical flat-topping, mechanical V-Cut, and hand pruning from pruning towers using hydraulic-powered saws) were established in a randomized complete block design, with treatments implemented over 0.54 acre rows.  All treatments other than the standard hand-pruning treatment were followed by less-detailed hand-pruning, using pole saws and pole lopers from the ground. Within each of three blocks, treatments were implemented over three consecutive rows, with all data collected from the central row. Pruning treatment affected tree height, with flat topped rows exhibiting significantly shorter height than other treatments.  Pruning treatment did not affect canopy light interception. Neither fresh nor dry yield was affected by pruning treatment; however, one block exhibited higher yield than the other two blocks. Use of pruning towers plus a cursory follow-up with hand pruning from the ground resulted in increased fruit size as estimated by dry fruit weight; however the distribution of fruit within size categories was not affected, suggesting that pruning treatments would not affect fruit value based on size.  The results suggest that mechanized pruning techniques may be employed without adverse affect on yield or fruit size; however, implementation of these treatments over successive years is necessary to evaluate the long-term implication of pruning treatments on the economics of yield.