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Abstract Botrytis blight on petunia flowers causes significant losses in the postharvest environment. Infection occurs during greenhouse production, and symptoms are expressed during transport. This phenomenon is termed petunia flower meltdown because of the rapid collapse of flower petal tissue as the plants are transported from the production greenhouse to the retail store. The objective of this study was to determine the effect of calcium (Ca) spray applications on botrytis blight severity in petunia flowers. For the first experiment, petunia ‘Pretty Grand Red’ plants were sprayed twice per week for 2 weeks with calcium chloride (CaCl2) at rates of 0, 400, 800, and 1200 mg·L−1 Ca. A fungicide (cyprodinil, 37.5%; fludioxonil, 25%) was used as an additional control treatment. Twenty-four hours after the last treatment, freshly opened flowers were harvested, placed into a humidity chamber with 99% relative humidity, and inoculated with a Botrytis cinerea spore suspension (1 × 104 conidia/mL). Disease progression was recorded every 12 hours for 72 hours. The results showed a 96% reduction in botrytis blight severity as Ca concentration increased from 0 to 1200 mg·L−1 Ca. The Ca treatments provided better disease control than the fungicide treatment because of the fungicide resistance of the isolate used in the study. A second experiment was performed to determine whether the beneficial response to CaCl2 application was influenced by chlorine (Cl) or the electrical conductivity (EC) of the spray solutions, and no significant responses were observed. These studies prove Ca is the sole source of the reduction in botrytis blight severity following treatment with CaCl2 sprays, and demonstrate the benefit of using Ca as a tool for the management of botrytis blight on petunia flowers.