The objective of this study was to characterize the effects of barley powdery mildew infection on wheat via the evolution and dynamics of chloroplasts and oxidative processes based on in vivo measurements of ultra-weak photon emission, parallel measurement of chlorophyll and ascorbic acid content, and molecular identification of the pathogen. The results showed the temporal dynamics of the evolution of ultra-weak photon emission signals that were evidently different for healthy and powdery mildew-infested wheat leaves. In the dark, the ceasing of delayed fluorescence signal made it possible to visualize the ultra-weak luminescence signal as well. Both delayed fluorescence and ultra-weak luminescence signals were characteristic of stress symptoms induced by powdery mildew that was further strengthened by the changes of chlorophyll and ascorbic acid content as typical stress analytical parameters. The presented data and parameterization enabled the identification of stress induction due to powdery mildew infestation in wheat, which should be investigated in detail in the future for fine-tuning our measurements, even by using other species and increasing the length of the measurement in order to increase its specificity. The changes in R2 values are suitable for monitoring the changes of plant stress response. The measurement of fluorescence and luminescence leads to a greater comprehension of the underlying photon emission-related processes, both in general and in the case of powdery mildew infestation.