Abstract: Methods are provided for determining the effectiveness of a plant treatment agent in controlling a plant disease organism. The methods involve (a) applying the plant treatment agent to a substrate, (b) inoculating the substrate with the disease organism, and detecting photon emission from light-generating moieties. The methods also involve (1c) after a period of time in which the disease organism can grow, applying a pro-light-generating moiety which is selectively transformed by the disease organism or the substrate to a light-generating moiety, (1d) detecting photon emission from the light-generating moiety (e.g. over an area of the substrate), and (1e) determining the effectiveness of the plant treatment agent based on the amount of detected photon emission and/or the fraction of the substrate area from which photon emission is detected.