Southerly Extension of Poplar Leaf Blight (Linospora tetraspora) in the Pacific Northwest.

Poplar leaf blight caused by Linospora tetraspora G. E. Thompson (Ascomycetes, Valsaceae) is widespread on Populus balsamifera in Canada from Quebec to British Columbia (1). The only United States records of this northerly fungus are from Vermont, Wisconsin, and Alaska (1,2). There are no records of this fungus on the Pacific Coast south of British Columbia, despite the presence of susceptible hosts (i.e., Populus trichocarpa and its hybrids). However, in September of 1997, the disease was observed in a hybrid poplar plantation at latitude 47.9°N and longitude 122.1°W near Snohomish, Washington. Blight affected the lower crown of trees in their second year of growth. Leaf lesions, with their characteristic black stromata, were easily distinguished from symptoms of other diseases. Some individual lesions of L. tetraspora affected entire leaf laminae, but there appeared to be little premature defoliation at the time of observation. Populus trichocarpa × P. deltoides hybrids were more commonly blighted than were P. trichocarpa × P. maximowiczii hybrids (i.e., 13/18 clones affected versus 4/11, respectively). A voucher specimen was deposited in the Herbarium at the Pacific Forestry Centre (DAVFP 25289). References: (1) M. E. Barr. Mycol. Mem. No. 7:130, 1978. (2) D. F. Farr. et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.