This study was carried out on Uzun and Siirt pistachio cultivars present at the Pistachio Research Institute orchards. After the most suitable pruning, fertilization and irrigation practices, different plant growth regulators were sprayed on entire trees at the different doses, and effects of plant growth regulators on alternate bearing were investigated. In the study, 10, 25 and 50 ppm 1-Naphthaleneacetic acid (NAA), 25 ppm Nbenzyl-9-(2-tetra-hydropyranyl) adenine (BA) and 0.25% urea were used, and 0.25% urea was added to all plant growth regulators' doses. Plant growth regulators were sprayed to the fruits, buds and leaves to the point of drip. Applications were done two times in year. First application was done at starting kernel development, and second application was done 20 days after the first application. According to the results, the highest yield was obtained from 25 ppm benzyladenine + 0.25% urea in Uzun (4.98 kg per tree) and 47.29% of inflorescence buds retained in this application. The lowest yield was obtained from control as 4.05 kg per tree and 47.56% of inflorescence buds retained in control. At the Siirt, the highest yield (8.26 kg per tree) was obtained from 0.25% urea application and 51.58% of inflorescence buds retained in this application. The lowest yield was obtained from 50 ppm naphthalene acetic acid application (5.16 kg per tree) and 58.49% of inflorescence buds retained in this application. At the Siirt, 5.53 kg yield per tree was obtained from control and 6.01 kg per tree obtained from 25 ppm benzyladenine + 0.25% urea.
