Cyclic Occurrence of Sclerotinia Wilt of Sunflower in Western Canada. H. C. Huang, Plant Pathologist, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1. G. C. Kozub, Statistician, Agriculture Canada Research Station, Lethbridge, Alberta, Canada T1J 4B1. Plant Dis. 74:766-770. Accepted for publication 11 March 1990. Copyright 1990 Department of Agriculture, Government of Canada. DOI: 10.1094/PD-74-0766.

Field studies in Manitoba and Alberta revealed that Sclerotinia sclerotiorum may cause wilt of sunflower (Helianthus annuus) at any stage of growth but that the disease occurs mainly in two cycles: the first during seed germination and seedling establishment and the second from bud formation through seed development. Increase of wilt at the vegetative growth stage between the two disease cycles is low. In greenhouse and field experiments using artificial inoculation of sunflower with light brown, brown, black, or black, injured sclerotia, the first cycle of wilt at the establishment stage was attributed to myceliogenic germination of incompletely melanized or injured sclerotia. The second cycle of wilt may possibly be attributable to myceliogenic germination of black sclerotia, induced by exogenous nutrients.