Etiology and Control of Alternaria Blight of Poinsettia. 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 Hawaii, Honolulu 96822. Plant Dis. 70:73-75. Accepted for publication 5 August 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-73.

Blight of poinsettia (Euphorbia pulcherrima) bracts, leaves, and stems was shown to be caused by Alternaria euphorbiae comb. nov. Bract lesions, circular to elliptical when small, then expanding to irregular shapes up to 40 mm across with a tan or light brown central area, were surrounded by dark brown zones with purplish black borders. Leaf lesions were irregular, elongate, or angular along veins up to 20 mm across, and dark brown. Lesions on green stems were elliptical, up to 3 × 20 mm, and tan to medium brown with dark borders. These lesions occasionally expanded to girdle stems, resulting in wilting of terminal parts. Iprodione or anilazine provided excellent control in greenhouse studies.

Keyword(s): Euphorbia marginata.