The reasons and mechanisms of yearling and inflorescence shedding in pistachios are not exactly known. Iranian Pistachio Factors that accelerate the fall of inflorescence buds should be identified to control the annual growth of pistachios. Pistachio trees produce their produce on one-year-old leafless wood, and flower blooms occur before the leaf surface develops on the wood this year and before the ability to photosynthesize. Growth and development of pistachio fruit occurs from early April to mid-September, while new shoots begin to grow in late March to mid-March, and the inflorescence buds begin to grow and specialize on the branch for flowering the following year. They grow this year and continue until June. The formation of inflorescence buds and their subsequent shedding causes annual growth in pistachio trees. Unlike other fruit trees, the number of dedicated flower buds per year is low. Yearling in pistachios is related to the following: Competition for food resources The effect of hormones originating or accumulating in the brain Leaf area value The amount of carbohydrates available Number of pistachios on the branch with the product Brain growth and development