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Cryptocline cinerescens and Discula quercina Causing Twig Blight of Oaks in California. E. I. Hecht-Poinar, Department of Plant Pathology, University of California, Berkeley 94720. J. R. Parmeter, Department of Plant Pathology, University of California, Berkeley 94720. Plant Dis. 70:800. Accepted for publication 18 March 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-800d.

Extensive, previously unrecorded twig blight of Quercus agrifolia Née and, to a lesser extent, of Q. lobata Née and Q. wislizenii A. DC. have appeared in California during the past 5 yr. Cryptocline cinerescens (Bub.) v. Arx (1) and Discula quercina (West) v. Arx (2) were consistently isolated from diseased twigs. Pathogenicity was confirmed by Koch’s postulates, using conidial suspensions on greenhouse seedlings of Q. agrifolia. The two fungi were distinguished by size of conidia (av. 8.2 × 12.4 μ and 2.5 × 6.6 μ, respectively). Conidiospore masses of C. cinerescens were dark, and those of D. quercina were pink. Only current year’s growth was affected, and wounds were not required for infection. Symptoms appeared in July, and dead leaves clung to the twigs throughout the winter. Acervuli were produced at the base of infected twigs. Symptoms of the two twig blights were similar and quite distinct from dieback caused by Diplodia quercina, which affects mainly larger branches (1–6 in. in diameter). Susceptibility to twig blight varied, and severely affected trees were found beside unaffected ones. Trees infected repeatedly and heavily have died.