Mechanical pruning as a new approach to manage alternate bearing of ‘Sirora’ pistachio trees

Abstract

Pistachio is an alternate bearing species. To overcome alternate bearing, mechanical pruning was trialled. Mechanical pruning, 1-side slant topping, across 4 continuous years showed much better results with even yield. With mechanical pruning, the pruning angle becomes an important factor to control flower bud formation in the following 2 years. This approach becomes a direct control compared with traditional methods. The trial was to test, in which winter (prior to on- or off-year), mechanical pruning showed maximum benefit. 7-years' data did not show clear differences. Practically, heavier pruning prior to an off-year would be much easier for growers to accept. Also, the pruning prior to on-year did not benefit the immediate off-year. From this it would seem to be unnecessary to take this 1 year action earlier. After mechanical pruning, winter 1 had no flower buds but just strong shoot growth. Winters 2 and 3 had reasonable amounts of flower buds. Winter 4 had not enough flower buds and a loss in production. To reduce long shoots, authors also tried mechanical tipping just 1 year after 1-side slant topping. Comparing with non-tipping trees, tipping trees reduced flower buds. Reasons are discussed. Fifteen years' production data showed that mechanical pruning mitigated alternate bearing. Comparing 2-years averages, regular bearing had higher averages than alternate bearing.