Disease Note.

Canola Winter Decline Syndrome. C. B. Hill, Ameri-Can Pedigreed Seed Co., 7664 Moore Road, Memphis, TN 38120. D. V. Phillips, and D. E. Hershman. Department of Plant Pathology, Georgia Experiment Station, Griffin 30223; and Department of Plant Pathology, University of Kentucky Research and Education Center, Princeton 42445. Plant Dis. 76:861. Accepted for publication 13 March 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0861B.

Many producers of canola (Brassica napus L.) in southeastern and midsouthern states have experienced a gradual reduction of winter canola stands during the late winter and early spring months. Taproots and crowns of affected plants deteriorate and often become hollow. Plants may die before or during bolting, depending on the timing and degree of root and crown deterioration. Many plants appear to bolt normally but lodge later because of weakened crown tissue; others remain upright but die prematurely, with severely reduced seed yield. Stands may be reduced by over 90%. The proposed name for this malady is winter decline syndrome (WDS). While the exact cause is unknown, WDS appears to follow physical damage to roots, crowns, or stems caused by 1) sublethal low temperatures that injure plants that have bolted prematurely or are not adequately cold-hardened. 2) plant heaving, and! or 3) depletion of soil oxygen resulting from waterlogged soils. Physical damage provides ports of entry for invasion by a variety of secondary organisms. Soilborne bacteria (Xanthomonas sp., Clavibacter sp.) and fungi (Rhizoctlonia sp., Fusarium sp.) have been isolated from affected tissue, but there has been no consistent pattern of isolations. in addition, affected roots and crowns are frequently, but not always, infested with seedcorn maggots (Delia platura (Meigen). Severity of WDS differs among cultivars.