Healthy plants are saleable plants and are key in a lucrative flower business. Clean stock programs are foundational to successful flower enterprises. Since flowers bring aesthetic pleasures to humanity and the beauty is enhanced by health, then disease-free production is even more important. Chrysanthemums are sold as cut flowers, as potted flowering plants, or as garden plants. During the first half of the twentieth century, as the chrysanthemum industry was being developed, devastating diseases had to be overcome in order for the business to survive. Methods had to be developed to detect systemic fungal and bacterial pathogens and later expanded to include virus and viroid pathogens in order to deliver clean plant products to customers. Visual inspection could not adequately detect vascular pathogens or virus/viroid pathogens that did not express symptoms until flower. The procedures developed by specialist propagators combined with fungicides have been so effective that fungal diseases such as Ascochyta, Septoria and Verticillium no longer cause major losses and many growers today do not recognize diseases that were a constant menace in the past.