To evaluate the effects of chemical and hand fruit thinning on pistachio flower bud retention, experiments were conducted during 1382 and 1383. In the first year, ethephon treatments at the concentrations of 100 and 200 mg L^-1, urea at 2.5% and 5%, naphthaleneacetic acid (NAA) 125 and 250 mg L^-1 and naphthaleneacetamide (NAD) 250 and 500 mg L^-1 were sprayed on two branches of nine uniform trees with four replications. During the second year, hand fruit thinning treatments were used in addition to the previous treatments. Chemical treatments reduced flower bud abscission among them ethephon treatments were the most effective on flower bud retention. As compared with other treatments, hand thinning treatments had also positive effect on flower bud retention. Fruit thinning also increased kernel weight, reduced the number of nuts per ounce and decreased blank fruits. Fruit thinning had no significant effect on the yield of branches during ‘on’ year.

Keywords: Hand thinning, Chemical thinning, Alternate bearing, Pistachio.

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