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Etiology and Control of Poinsettia Blight Caused by Phytophthora nicotianae var. parasitica and P. drechsleri. M. A. Yoshimura, Department of Biological Science, California Polytechnic State University, San Luis Obispo 93407. J. Y. Uchida and M. Aragaki, Department of Plant Pathology, University of Honolulu, HI 96822. Plant Dis. 69:511-513. Accepted for publication 11 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-511.

A blight of poinsettia (Euphorbia pulcherrima) leaves, bracts, and cyathia was shown to be caused by Phytophthora nicotianae var. parasitica and P. drechsleri. Leaf lesions, initially grayish brown, turned brown to black, expanded into irregular shapes, and elongated along veins. On bracts, lesions were purple to brown, spread very rapidly, and blighted large areas or entire bracts. Black lesions that expanded rapidly into rots were characteristic on cyathia. Fosetyl Al and ethazol were not effective at the rates tested for control of this disease. Metalaxyl as soil drenches at 6 or 12 mg a.i./960 cm3 of potting medium provided excellent control of poinsettia blight.