ANNUAL AND BIENNIAL MECHANICAL PRUNING OF HEDGEROW ENGLISH WALNUTS

Annual and biennial mechanical pruning were compared for 6 years in a ‘Chico’ walnut (Juglans regia L.) hedgerow orchard (6.6 x 3.3 m, 450 trees/ha) planted in 1974 at Vina, CA. Pruning was performed with a vertical boom hedging machine positioned to side hedge 1.3 m from the trunks. The experiment also included standard hand-pruned trees (6.6 x 6.6 m, 225 trees/ha). Yield from trees hedged annually on alternate sides (one side each year) was significantly greater than yields from trees hedged annually on two sides or hand-pruned and standard density. Yields from biennially hedged trees (two sides pruned in either even or odd years) fluctuated widely with greater yield than alternate-side hedging during years in which trees were not pruned, but less in years following pruning. Nut size varied inversely with crop load, but biennial hedging resulted in smaller nuts than alternate-side hedging, even though the average yield was similar. Thus, alternate-side hedging of lateral-bearing walnut hedgerows appears to be the preferred pruning procedure and may provide sustained high productivity and quality in addition to the other advantages commonly attributed to high-density hedgerow systems.