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Disease Note.

Powdery Mildew Caused by Erysiphe cichoracearum on Five New EucalyptusHosts in Arizona. M. E. Matheron, Yuma Agricultural Center, University of Arizona, Yuma 85364. J. C. Matejka, Yuma Agricultural Center, University of Arizona, Yuma 85364. Plant Dis. 76:1077. Accepted for publication 9 July 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1077D.

In February 1992, conidia and mycelia of powdery mildew were observed on I-yr-old plants of Eucalyptus cladocalyx F.J. Muell., E. viminalis Labill., E. camaldulensis Dehnh., E. leucoxylon F.J. Muell., and E. polyanthemos Schauer growing in a greenhouse in Arizona. E. citriodora Hook., E. globulus Labill., and E. maculata Hook. plants of the same age in the same greenhouse showed no symptoms of the disease. Both sides of leaves of affected plants were covered with mycelia and conidiophores. The ellipsoid conidia were in chains, did not contain fibrosin bodies, and conformed to those of Erysiphe cichoracearum DC. At the time symptoms appeared, maximum and minimum temperatures in the greenhouse were 32.5 and 16.3 C, respectively. This pathogen has been described on 11 species of Eucalyptus growing in greenhouses in California (1), but this is the first report of E. cichoracearum in the United States on the species of Eucalyptus named here.

Reference: (1) M. W. Gardner et at. Plant Dis. Rep. 54:399, 1970.