Powdery mildews on lilac in western North America include Phyllactinia syringae, sp. nov.

ABSTRACT

Two powdery mildews, Erysiphe syringae and the previously undescribed Phyllactinia syringae, sp. nov., occur on lilac in western North America. Phyllactinia syringae is found on common lilac, whereas E. syringae is found on Chinese lilac and, occasionally, common lilac. Infection by P. syringae is extremely unobtrusive until formation of a hypophyllous mycelial mat with chasmothecia in late fall. Infection by E. syringae in late summer is conspicuous, with its thick, superficial mycelial mat on the leaf upper surface detracting from the aesthetic appearance of the bush.

KEYWORDS:

• Erysiphe syringae
• E. syringae-japonicae
• morphology
• Phyllactinia fraxini
• Syringa vulgaris
• S. × chinensis.

ACKNOWLEDGMENTS

A. W. Ramaley provided the first known collections of P. syringae (RMS 48256 and RMS 48255, collected in 1984 and 1986, respectively) and suggested then that the mildew probably was an undescribed species; for this reason, we include her as one of the authorities for the new species. S. Thomson provided the specimen from Logan, Utah (RMS 48259). Finally, we thank the staff of the RMS for assistance with the deposition of specimens.

This article is a Colorado Agricultural Experiment Station Research Publication (Project 1-50779).

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