Improving the efficiency of pesticides through biological additives is an effective strategy for reducing application dosages. This study was conducted to evaluate the effect of adding natural mineral biochar on the efficacy of spirodiclofen in controlling the common pistachio psylla (Agonoscena pistaciae) under field conditions. The experiment was carried out in a completely randomized design (CRD) with three treatments: control (water), spirodiclofen SC24% (35 ml/100 L), and a combination of spirodiclofen SC24% (35 ml/100 L) and natural mineral biochar (2.5 kg/100 L), with five replications in the orchards of Kerman in August 2025. Populations of 1st to 5th instar nymphs were monitored on days 0, 3, 7, 14, and 21 post-application.

The results indicated that the effect of treatments on the number of live nymphs was significant across all time intervals (P < 0.05). On the third day post-application, the combination treatment (pesticide + biochar) exhibited a significantly lower number of live nymphs compared to the pesticide-only treatment. This initial increase in efficacy is likely attributable to the physical abrasion of the cuticle by biochar particles, which facilitates the penetration of the pesticide into the pest's body. Although the mean number of live nymphs in the combined treatment remained lower than the pesticide-only treatment on days 14 and 21, this difference was not statistically significant (P > 0.05). Overall, by further reducing the initial nymph populations, the addition of mineral biochar demonstrates high potential as a supplement in integrated pest management (IPM) programs for pistachio.