This study examined lipid peroxidation and the dynamics of the enzymatic antioxidant response in winter triticale under herbicide stress, as well as the possibility of alleviating oxidative load through the co-application of a plant growth regulator of natural origin. Field and laboratory studies were conducted in 2023–2025 under the conditions of the Right-Bank Forest-Steppe of Ukraine. The herbicide Dialen Super was applied at rates of 0.8, 1.0, and 1.2 L/ha, alone and in combination with the plant growth regulator Kelpak (2.0 L/ha). Lipid peroxidation intensity was assessed by malondialdehyde content, and the enzymatic antioxidant response by the activities of the enzymes catalase and peroxidase. On the 5th day after treatment, malondialdehyde content under the herbicide exceeded the control by 64.7–111.0%, while catalase and peroxidase activities exceeded it by 40.3–77.6% and 40.5–81.0%, respectively. The addition of Kelpak reduced malondialdehyde content by 22.3–24.0% on the 5th day and by 20.2–29.9% on the 10th day compared with the corresponding herbicide-only treatments. On the 5th day, Kelpak additionally increased catalase activity by 16.9–18.0% and peroxidase activity by 20.4–22.7%. On the 10th day, the action of the plant growth regulator was accompanied by consistently lower malondialdehyde content and decreased peroxidase activity relative to the corresponding herbicide-only treatments; the catalase response depended on the herbicide rate. Taken together, the obtained indicators characterize an alleviation of the examined component of herbicide-induced oxidative stress.