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Canker diseases in northwestern forest nurseries have been referred to collectively as top blight. To distinguish among the various symptoms and their associated fungi, we made systematic observations of and isolations from Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings through two crop cycles in four northwestern nurseries, and suspect fungi were subjected to pathogenicity testing. Five diseases were distinguished. Hypocotyl rot, caused by Fusariumoxysporum, kills seedlings during their first growing season. Upper stem canker, caused by Phomaeupyrena and Fusariumroseum, girdles seedlings in midstem in the fall of their 1st year. Lower stem canker, also caused by P. eupyrena and F. roseum, kills seedlings in the winter or early spring of their 2nd year and is associated with soil collars built up by splashing water. Botrytis and Phomopsis cankers occasionally kill new shoots during the 2nd year. Not all diseases are damaging every year or in all nurseries.
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Hansen et al. (1988) studied this question.
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