2019 ASHS Annual Conference

A six year trial, three alternate bearing cycles, trial investigated the effect of timing of mechanical topping and hedging on alternate bering in Pistacia vera cv. 'Kerman' female tree on four different rootstocks; P. atlantica, P. integerrima, P. atlantica X P. integerrima, P. integerrima x P. atlantica. Results demonstrated that both yield and alternate bearing were affected by rootstock. Trees on P. atlantica, P. integerrima, P. atlantica X P. integerrima, and P. integerrima x P. atlantica produced an average of 3823, 4641, 5433 and 5634 annual pounds per acre respectively. As demonstrated in an earlier trial alternate bearing of trees on a P. atlantica rootstock was more effectively mitigated by mechanical topping and hedging entering a low crop year versus a high crop year; the respective alternate bearing indexes in this trial were 0.41 and 0.79. The same treatment was equally effective on the less alternate bearing trees on the P. integerrima rootstocks; mechanical topping and hedging entering a low crop year versus a high crop year produced alternate bearing indexes of 0.21 versus 0.55. For 'Kerman' trees on the P. integerrima, P. atlantica X P. integerrima, and the P. integerrima x P. atlantica hybrid rootstocks the alternate bearing indexes were significantly lower than on single species rootstocks, virtually identical and unaffected by mechanical topping hedging entering the high or low crop year. The 'Kerman' scion on the P. integerrima x P. atlantica hybrid rootstock had an alternate bearing index of 0.27 when pruned entering both the high and low crop year. The 'Kerman' scion on the P. atlantica X P. integerrima rootstock has an alternate bearing index of 0.29 if topped and hedged prior to the low crop year and 0.30 if pruned entering the high crop year. The results demonstrate that that the current commercial rootstocks in California not only have a significant effect on both yield and alternate bearing of the 'Kerman' female scion but also produce significantly different reactions to mechanical topping. It appears the vigor of the P. integerrima parent confers the ability to decrease alternate bearing.