An invert emulsion (water-in-oil formulation) based on coconut and soybean oils provided the most stable emulsion layer (93% V/V) and lowest viscosity (27±0.81 cps), suitable for a formulation of Trichoderma harzianum conidia. Conidia remained viable for 36 months (shelf-life) with 50% reduction in viability (half-life) after 5.3 months at 20±1°C., compared with 2.7 and 0.7 months, respectively, for dry non-formulated conidia. Stability and viscosity of the formulation remained constant during the time period of viability study. Bio-assay tests on wounded apple fruit indicated the presence of significant preventive effect of formulatedTrichoderma conidia against the causative organism of apple gray mold Botrytis cinerea. The diameter ofBotrytis lesions was significantly reduced (P<0.05) 5 days after inoculation and treatment with formulatedTrichoderma conidia. Botrytis sporulation on the lesion surface was also inhibited 10 days after inoculation. These results were confirmed under simulated natural conditions by spraying a Botrytis conidial suspension on microwounded apple fruit following treatment by dipping fruit. Treatment of healthy non-wounded apple fruits resulted in protection from Botrytis infections for >2 months following inoculation and treatment.