The potent antioxidant N-acetylcysteine amide (NAC amide), or a physiologically acceptable derivative, salt, or ester thereof, is topically or exogenously applied to a plant, or part thereof, to reduce or prevent adverse reactions of plants and crops to environmental biotic and abiotic stresses, such as extremes of temperature, drought, humidity, frost, rain, as well as the presence or invasion of a variety of pests and pathogens. Such environmental stresses can result in oxidative stress and the correlated production (and buildup) of free radicals in plant cells, which damages plant cells and tissues and can lead to plant death. NAC amide reduces, prevents, alleviates, or otherwise counteracts such oxidative stress and free radical production, which adversely effect the overall growth and viability of the plant.