Disease Note

Mycosphaerella laricina on European Larch in Vermont. D. R. Bergdahl, Department of Forestry, University of Vermont, Burlington 05405. S. S. Halik, and D. L. K. Smeltzer, Department of Forestry, University of Vermont, Burlington 05405. Plant Dis. 69:83. Accepted for publication 14 September 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-83A.

Premature defoliation of European larch (Larix decidua Mill.) was first observed in Chittenden County, Vermont, during 1983. In the fall, needles bearing black acervuli with conidia were collected from European larch. Hyaline conidia were mostly three-septate with rounded tips and truncate bases and were 16–29 μm long (av. 22.3 μm). In June 1984, perithecia were found on needles that had overwintered on the ground. These perithecia had mature asci 36.3–50.6 μm long (av. 38.7 μm) and contained hyaline ascospores averaging 14.2 × 3.3 μm. These measurements are similar to those reported for Mycosphaerella laricina (Hart.) Neg.; R. F. Patton has confirmed our identification of M. laricina on European larch. This report extends the known geographic range of this fungus in the United States to include part of New England.