The Koch (Acari: Tetranychidae) is one of the primary pests affecting buckwheat, and its management has become increasingly critical. Entomopathogenic fungi offer a promising way to solve this problem by providing both pest control and disease resistance, as well as promoting plant growth through endophytic colonization. This study investigated the effects of applying (Liang) Samson & Hywel-Jones and (Bals.-Criv.) Vuill. on different buckwheat varieties, and analyzed the physiological indices of buckwheat, the population of and (Ehara & Lee). Results showed that the optimum concentration for fungal colonization on buckwheat was 1 × 10 spores/mL. The combined application of and significantly enhanced buckwheat growth, with root length, plant height, main stem diameter, fresh weight, and dry weight reaching 63.3 mm, 24.1 cm, 2.1 mm, 2.0 g, and 0.1 g, respectively. The highest escape rate of was 76.33%. Furthermore, the combined application of mixed fungal suspension and had the best control effect on , with pest suppression exceeding 97.83% and an oviposition as low as 0.25 eggs per female. This study is the first to demonstrate that the joint application of and can promote buckwheat growth and, when combined with predatory mites, effectively control These findings provide a theoretical basis for the development of integrated biocontrol strategies combining entomopathogenic fungi and predatory mites.