Ornamental crop production systems face low tolerance of aesthetic crop damage by consumers and during exports by quarantine inspection entities. Consequently, development and testing of pesticide applications on ornamental crops involve two equally important assessments: 1) demonstrate the ability of pesticides to suppress target pest populations significantly and 2) minimize risks of applied pesticides causing phytotoxicity of leaves, shoots, and flowers. To maximize the accuracy and repeatability of phytotoxicity assessments, it is paramount that methods of detection and diagnosis that are rapid, repeatable, and quantitative be developed and promoted. We performed visual phytotoxicity inspection of three ornamental plants [zinnia (Zinnia elegans), marigold (Tagetes patula), and gerbera (Gerbera sp.)] to a numbered compound applied at three doses. The same plants were also subjected to optical (remote) sensing and classified as having either no or low phytotoxicity response. Although results from visual inspections suggested very low levels of phytotoxicity, 32 of 40 plants (80%) were classified correctly based on optical sensing. Importantly, classified plants showed no significant morphometric differences. We provide proof-of-concept results that optical sensing may be used to detect accurately even highly subtle stress responses by ornamental plants to high doses of foliar pesticides.