Evaluation of Poinsettia Cultivars for Susceptibility to Powdery Mildew

Powdery mildew ( Oidium spp. Link) on poinsettias ( Euphorbia pulcherrima Willd. ex Klotzsch) growing in commercial greenhouses was first observed in the United States in 1990. Susceptibility of poinsettia cultivars (`Freedom Red', `Hot Pink', `Jingle Bells 3', `Pink Peppermint', `Red Sails', `Supjibi Red', `Topwhite', `V-14 Glory', `V-14 Pink', `V-14 White', `V-17 Angelika White') to powdery mildew was investigated using 8- to 10-week-old poinsettias with mature bracts. Area under the incidence of disease progress curve was used to express the incidence of bracts infected over 31 d after inoculation. Three cultivars with red bracts (`Freedom Red', `Supjibi Red', `Red Sails') had significantly more infection than the other cultivars in both experiments, while one cultivar with white bracts (`V-17 Angelika White') had significantly less infection.