Flight abilities and dispersal distances of males of irradiated vs. untreated European grapevine moths (Lobesia botrana [Denis & Schiffermüller]: Lepidoptera: Tortricidae) were assessed in a flight assessment cage and in a vineyard. Newly emerged adult male moths were either untreated or γ-irradiated either with 150 Gy or 350 Gy, and each group was marked with a different colored fluorescent dust. Males were released in a laboratory flight assessment cage (70 × 40 × 50 cm) and at the center of a vineyard. The flight assessment cage test revealed significant differences in the flight responses of irradiated and untreated L. botrana males to calling females during the first 2 days after the initiation of the test. The greatest percentage of non-flying males (47%) was observed in the 350 Gy-treatment, whereas no significant differences were detected in male flight ability between untreated and 150 Gy γ-irradiated male moths. Six hundred male moths were released in a vineyard with a rectangular trapping grid around a central release point, and traps were baited with a synthetic pheromone. One hundred and thirty one males (21.8%) were recaptured, with the farthest being caught 40 m from the release point. No differences were observed in male field performance between 150 Gy γ-irradiated and untreated male moths, whereas 350 Gy γ-irradiated males showed limited field dispersal when compared with either 150 Gy γ-irradiated or untreated male moths. The results, the values of several attributes (flight ability, dispersal distance and recapture rate of released males in pheromone-baited traps)—which are critical for effective population suppression by the sterile insect technique with inherited or F₁ sterility (SIT/F1)—were significantly decreased by increasing the radiation dose applied to L. botrana males from 150 Gy up to 350 Gy. The flight assessment cage proved to be a valuable tool for measuring differences in the quality of untreated and irradiated moths.