US: The plight of the poinsettia with aerial blight
Poinsettia’s (Euphorbia pulcherrima) are susceptible to a variety of pathogens when grown in a greenhouse. Some common diseases, such as bacterial soft rot, Botrytis blight, poinsettia scab, powdery mildew and a variety of root rots, as well as insect and production issues, are outlined in “Common greenhouse poinsettia production problems” from Michigan State University Extension, However, certain species of the pathogen Phytophthora, that is typically thought of as a root rot, can also cause issues above-ground.
Phytophthora is a water mould pathogen that can be splashed onto stems and foliage and cause an aerial blight. Symptoms of aerial Phytophthora include brown or purple-black stem lesions that may spread quickly to bract petioles causing the bracts to wilt. Leaf lesions are also possible and will be greyish brown at first and then turn to brown to black. Growth of this disease is promoted by wet conditions and overhead irrigation spreads the infection from plant to plant.
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