Two experiments were conducted to determine the effect of ozone treatment on controlling deterioration of high-moisture maize under extreme and moderate environmental conditions experienced during harvest. In the first experiment, 0.77-kg maize samples held at 22% moisture content were treated with ozone at 0.08, 0.16, 0.31, 0.62, 0.94, 1.25 and 1.56mgkg maize −1 min −1 (60–1120ppm ozone in air during application) for periods of 5 or 24h, with an additional treatment of 1.56mgmin −1 repeated every 3d, and stored at 32°C for 9d under continuous aeration. Ozone treatment decreased dry matter loss compared to the control, but not to a level that would likely justify ozone treatment at the rates and treatment times used. In the second experiment, 2.43-kg maize samples held at 26% moisture content were treated with ozonation rates of 0.25, 0.5, 1, and 2mgkg maize −1 min −1 (1090–8680ppm ozone during application) for 24h, stored at 15.5°C for 30d and passively aerated every 3d. Additional ozone treatments at the 2mgkg maize −1 min −1 rate were applied for 1h on 3-, 6-, and 12-d intervals throughout the experiment. Single ozone treatments of 1 and 2mgkg maize −1 min −1 were equally effective, reducing dry matter loss by 1.3 percentage points compared to the control after 30d of storage. Repeat treatments at 2mgkg maize −1 min −1 did not reduce dry matter loss compared to the single treatment.