Disease Note

Needlecast of Western Larch Seedlings Caused by Mycosphaerella laricina. M. E. Ostry, North Central Forest Experiment Station, USDA Forest Service, St. Paul, MN 55108. T. H. Nicholls, and M. A. Palmer, North Central Forest Experiment Station, USDA Forest Service, St. Paul, MN 55108. Plant Dis. 69:542. Accepted for publication 7 March 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-542b.

Western larch (Larix occidentalis Nutt.) seedlings in northeastern Iowa and southwestern Wisconsin are highly susceptible to Mycosphaerella laricina (Hart.) Neg., a fungus recently reported on European larch (L. decidua Mill.) in the United States. To test their susceptibility, western larch from an Oregon seed source and European larch from nine seed sources were planted in 1984 in completely randomized blocks with four replicates on the edge of stands of infected European larch. Seedlings were evaluated for infection in September 1984. Western larch was uniformly severely diseased, whereas European larch varied in susceptibility by seed source. On seedlings that had been defoliated early, refoliated needles were also infected. M. laricina may threaten western larch if introduced into the western United States.