Evaluation of effects of two spring applications of micronutrients on the population density of common pistachio psylla (Agonoscena pistaciae) in pistachio orchards

The common pistachio psylla, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Aphalaridae) is one of the most detrimental pests to pistachio trees. This pest is distributed throughout all the pistachio producing regions of Iran. Nowadays various pesticides are used to control the common pistachio psylla, but extensive pesticide spraying against this pest over a period of several years has overpowered its natural enemies. Moreover, the overlapping of generations has resulted in an abundant presence of the pest. Many herbivorous insects can make qualitative distinctions between host plants, they can feed and oviposit preferentially on higher quality plants. Cultural methods such as crop fertilization can affect the susceptibility of plants to insect pests by altering a plant tissue's nutrient level. This study tested nitrogen (N), calcium (Ca) and zinc (Zn) fertilizers on A. pistaciae in pistachio orchards. The experiment was based on complete randomized blocks with three replications and nine treatments including once-applied Zn, Ca, N, NCa, ZnCa, ZnN, ZnCaN, pesticide (amitraz) and a control (distilled water), on common pistachio psylla fed on 20-year-old pistachio trees of Ahmadaghaei rootstock. The results demonstrated that the effect of nutritional solutions on nymph and egg populations showed a significant difference at a 5% level. The highest measure of control on eggs was related to amitraz, ZnCa and Zn while the least was related to NZn. The results also showed that the highest measure of pest control was related to Ca while the least was related to N and Zn. The results indicated that combinations of the elements mentioned had a stronger reducing effect on the concentration of pistachio psylla nymphs than the effect pesticide had.