The lacy white patches seen on this poinsettia may resemble snowflakes, but they are powdery mildew caused by the fungus, Oidium. High temperatures are a contributing factor to this disease. Fungicides are utilized to control and prevent this problem during commercial production of poinsettias. This image is from the APS Feature story, Poinsettia: The Christmas Flower by D. M. Benson, J. L. Hall, G.W. Moorman, M. L. Daughtrey, A. R. Chase, and K. H. Lamour
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