DOES CANOPY MANAGEMENT HELP TO ALLEVIATE BIENNIAL BEARING IN ´ENNIS´ AND ´MONTEBELLO´ HAZELNUT TREES IN OREGON?

Biennial bearing in ‘Ennis’ is pronounced in young trees, and can have an influence on nut quality as well as yield. A 0.6ha block of ‘Ennis’ trees planted in 1983 on 3.05 m x 6.10 m spacing was used from 1993 to 2002. Three pruning treatments were applied: no pruning except removal of dead wood, selective scaffold removal (SSR), and removal of alternate trees. Alternate trees were heavily pruned in 1994 and 1995 prior to their removal. There has been less variation in yield in the pruned and unpruned trees over the past four years than in the tree removal treatment. When expressed on a yield per acre basis, there is little difference among all three treatments, even though there are half the number of trees in the removal treatment. Pruned trees (SSR) have had more giant/jumbo nuts than either unpruned or tree removal treatments in heavy crop years, but there has been no difference in nut size distribution in low crop years. In 1999, a heavy crop year, three pruning treatments were applied to three replicates of 39 trees each of ‘Montebello’ that were planted in 1985 on 5.5 m x 5.5 m spacing. Trees were either hand pruned or vertically hedged to remove 20-30% of canopy, or pruned lightly to remove dead wood and low hanging branches only. Mechanically hedged trees tended to have higher yields, fewer defects, and larger nuts.