Beauveria bassiana has proven to be an efficient crop colonizer due to its highly entomopathogenic activity against a wide range of sap-sucking pests. In this work, two different application methods of B. bassiana (Bals.-Criv.) strain PPRI 5339 were studied over two consecutive years: (A) seed coating on cotton and (B) trunk inoculation to kiwi trees. Untreated plants served as controls for both methods. The sucking insects, Aphis gossypii (Glover) on cotton plants, and Halyomorpha halys (Stål) on kiwi trees, were counted, and the total chlorophyll content and leaf area were measured as indicators of plant performance. The presence of B. bassiana slightly reduced the population of sucking pests but also enhanced the total chlorophyll content and the leaf area in both crops. These results demonstrate the dual role of strain PPRI 5339 as both a biocontrol agent and a growth promoter, highlighting its potential as an environmentally friendly alternative for managing sap-sucking pests that severely affect agricultural production in Greece.