A method and system of treating plants is provided. The method includes measuring optical properties of a plant using a plurality of spectral bands. The method further includes calculating in a computational device at least two vegetative indexes using the optical properties, each of the at least two vegetative indexes correlating to one or more plant growth parameters. The method further includes calculating in the computational device a water invariant chlorophyll index from at least two vegetative indexes using the plurality of spectral bands. The also provides for treating one or more of the plants based on the water invariant chlorophyll index.