Ozone (O₃) fumigation is a potential quarantine treatment alternative for controlling stored-product pests and surface insect pests on fresh agricultural commodities. We explored the effects of temperature, treatment time, controlled atmospheres, and vacuum in combination with O₃ to control two important pests of ornamental crops: western flower thrips, Frankliniella occidentalis (Pergande), and longtailed mealybug, Pseudococcus longispinus Targioni Tozzetti. Treatment parameters tested were O₃ concentrations from 0 to 3,800 ppm, treatment durations were from 30 to 120 min, vacuums were from 0 to 0.41 bar below ambient, temperatures were from 32.2 to 40.6°C, and controlled atmospheres were composed primarily of nitrogen, carbon dioxide, or breathing air [BA]. Treatment efficacy was enhanced by higher O₃ concentration and temperature, lower oxygen, and longer treatment times. Reduced pressure was not an important factor. Mealybugs were more difficult to kill than thrips. A 30-min treatment of O₃ at ≈200 ppm in 100% CO₂ at 37.8°C killed 47.9 and 98.0% of mealybugs and adult female thrips, respectively. All of the ornamentals tested were damaged to some degree by O₃ treatments. However, crops with thick leaves such as orchids exhibited little damage, and the waxy portions of certain flowers were not damaged. The results suggest that O₃ has potential as a quarantine treatment to control thrips and mealybugs on selected commodities.