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First Report of Hemp Canker Caused by Sclerotinia sclerotiorum in Alberta, Canada

Hemp (Cannabis sativa L.) is a herbaceous annual grown mainly for its blast fiber and seed oil. In 1999, Health Canada issued licenses to plant 12,145 ha of hemp in Canada. Of these, 730 ha were in Alberta. During the last week of August, hemp plants (cv. Fasamo) in a central Alberta field showed the following symptoms and signs: wilting foliage turning light brown; dry tan to gray lesions on stems; shredding and breaking of stems at the lesion; presence of white mycelium in the lesion; and black round, irregular, or oblong sclerotia (up to 5 mm diameter and 2 to 11 mm long) present externally at the lesion on the stem and inside the pith cavity. Lesions were found at the crown, near the inflorescence, and along the entire stem length. Disease incidence in a survey of six commercial fields (40 ha) ranged from 1 to 8%. The organism isolated from lesions on potato dextrose agar produced white aerial mycelia and large numbers of sclerotia characteristic of Sclerotinia sclerotiorum. Pathogenicity was confirmed by inoculating 23-day-old greenhouse-grown hemp plants (cv. Fasamo) with autoclaved wheat grains colonized for 14 days with a S. sclerotiorum culture previously isolated from an infected hemp plant. The grains were placed on soilless growing medium near the plant and covered very lightly. One week after inoculation, grayish lesions appeared on the stems, white mycelia appeared on lesions, and plants wilted. The pathogen was reisolated from the lesions. This is the first report of S. sclerotiorum on hemp in Alberta, Canada. The disease known as hemp canker has been reported to cause severe losses under cool wet conditions in the Netherlands (1).

Reference: (1) J. M. McPartland. J. Int. Hemp Assoc. 3:19, 1996.