Disease Note.

Leaf Mottle, a New Disease of Canarygrass Caused by Septoria triseti. B. Berkenkamp, Agriculture Canada Research Station, Melfort, Saskatchewan S0E 1A0. G. D. Jesperson, and J. Bissett. Saskatchewan Agriculture, Regina S4S 0B1; and Biosystematics Research Center, Agriculture Canada, Ottawa, Ontario K1A 0C6. Plant Dis. 73:859. Accepted for publication 5 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0859E.

In 1987, canarygrass (Phalaris canariensis L.) in central and northern Saskatchewan showed pale tan to gray, oval lesions with diffuse margins on leaf blades and sheaths. Later, numerous small, brown pycnidia formed in the lesions, and the distal portion of reaves died above large lesions. Septoria triseti Speg. was consistently associated with these symptoms. Conidiomata were pycnidial, subepidermal, dark brown, subglobose, and mostly 40-95 µm. Conidia were hyaline, filiform, straight or slightly curved, 17-34 X 1.4-2.2 µm, and aseptate or with one septum. Microconidia were occasionally produced in the same conidiomata with conidia or in separate spermagonia; they were hyaline, aseptate, filiform, straight actuate, and 5.5-9.6 X 0.7-1.0 µm. S. triseti was isolated from diseased leaves, and Koch's postulates were used to confirm pathogenicity on annual canarygrass in growth cabinets. In 1988, leaf mottle was the most widespread and severe disease of canarygrass in Saskatchewan, surpassing root rot and spot blotch.