This is responsible for the greatest economic losses in pistachio production. Early season feeding usually results in fruit drop, but late season feeding causes the staining and under-development of fruits, which remain on the tree. Sprays for control of these pests have apparently caused outbreaks of scale problems, perhaps due to elimination of the scale's natural insect predators. In Italy, Greece, and Asia Minor, much of the production is unirrigated through the rain-less summer months, and yields are low. In California, irrigation during the summer greatly increases production.
Pistachios thrive in hot, dry desert-like conditions like the central California valley.
Under cool conditions at higher altitudes, kernel development is poor. Pistachios are intolerant of high humidity during the growing season due to disease susceptibility. P. atlantica and P. terebinthus were traditionally the most popular stocks, with the former more readily available and easier to bud. P. terebinthus is more cold hardy and used by growers in colder areas. Both are susceptible to Verticillium wilt, and many orchards originally planted with these stocks have died.