Watch for bacterial leaf spots on poinsettias. Xanthomonas leaf spot on poinsettias begins with dull gray water-soaked areas. Yellow or tan spots can develop across the leaf. As the disease progresses, spots turn brown and angular so it could be confused with poinsettia scab. It is a good idea to send samples to the diagnostic laboratory if you see leaf spot symptoms.
Like all bacterial diseases, Xanthomonas is spread by water splash from overhead irrigation, high humidity and close plant spacing. If detected early, discarding plants showing symptoms and reducing leaf wetness help reduce disease spread. The use of bactericides such as Bacillus subtilus (Cease) or coppers (Phyton 27) may also help.
Reprinted from "Xanthomonas Leaf Spot on Poinsettias" by Leanne Pundt, University of Connecticut in the New England Greenhouse Update http://www.negreenhouseupdate.info/greenhouse_update/index.php.
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