Disease Note

Root Rot of Western Swordfern Caused by Phytophthora cinnamomi in California. T. E. Tidwell and K. L. Kosta, California Department of Agriculture, Sacramento, and J. C. Henderson, Placer County Department of Agriculture, Auburn, CA. Plant Dis. 68:536, 1984. Accepted for publication 3 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-536d.

Phytophthora cinnamomi Rands was isolated from discolored roots, crowns, and fronds of dying swordferns ( Polystichum munitum Kaulf.) and from soil sampled throughout the infested site.  Field symptoms included wilting of one to several fronds, with ultimate collapse of the plant.  The pathogen was inadvertently brought to the site via rhododendron nursery stock.  Pathogenicity was confirmed in greenhouse tests.  In both initial and repeated tests, root rot developed in inoculated plants but not in controls.  To our knowledge (based on manual and computer searches), this is the first report of a Phytophthora attacking a fern confirmed by the completion of Koch's postulates.

References: Bega, R. V. Plant Dis. Rep. 58:1069, 1974.