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Pest/Pathogen of the Month: August

Scientific name:  Sclerotinia sclerotiorum (Lib) de Bary.

Common names: white mold, cottony root, watery soft rot, stem rot, drop, crown rot and blossom blight.

Sclerotinia sclerotiorum (Lib.) de Bary is an Ascomycete fungus in the order Helotiales. This species is a multi-host necrotroph that infects more than 400 plant species, with lettuce, sunflower, canola and sugar bean being of economic importance to the South African agriculture industry. Sclerotinia sclerotiorum is characterized by the production of long-term survival structures called sclerotia which form an important part of the infection cycle. These structures can lay dormant in the soil for up to 8 years until environmental conditions become conducive for germination. Carpogenic germination of sclerotia results in the formation of a sexual structure (the apothecia) at soil level, which releases millions of ascospores that start the infection cycle. Myceliogenic germination forms hyphae and mycelium that results in direct sub-terrain infection of host plants, although this is limited to a radius of about 2 cm around the sclerotia. Signs and symptoms of disease depend on the host plant infected and can include water-soaked lesions or dry lesions on stems, leaves, fruits, or petioles. The presence of white fluffy hyphae on the host surface during high humidity forms the basis of the name “white mold” that refers to the disease. 

Photograph:Sclerotia (black structures) mixed in with soybean (Photo by Lisa Rothmann, taken from The South African Sclerotinia Research Network (SASRN) website)

 

 

New Publications

Botha I, Maduna SN, Hagen SB, Lall N, Berger DK. (2026) 3RAD-guided SNP discovery for species identification and conservation of the medicinal southern African tree Genus Greyia Hook. & Harv.. Ecology and Evolution 16(5):e73412, 1-29. 10.1002/ece3.73412
Balocchi F, Duncan G, Yilmaz N, Wingfield MJ, Paap T. (2026) The critically endangered geophyte Gladiolus aureus threatened by a wilt disease associated with Fusarium libertatis. Journal of Plant Pathology 10.1007/s42161-026-02227-7 PDF
Bose T, Wingfield MJ. (2026) Plantations are invasive pathogen bridgeheads—response to Li et al.. Trends in Ecology & Evolution 10.1016/j.tree.2026.05.006
Jamieson B-A, Paap T, Pegg GS, Carnegie AJ, Wingfield MJ, Roux J, Hardy GEStJ, Drenth A, Hammerbacher A, Bose T. (2026) Quambalaria spp.: Emerging Tree Pathogens of Concern. Current Forestry Reports 12:13. 10.1007/s40725-026-00274-y
Masuku SK, De Vos L, Thabiso TE, Steenkamp ET, Wingfield BD. (2026) Baseline sensitivity of South African Fusarium circinatum to tebuconazole. Journal of Plant Pathology 10.1007/s42161-026-02197-w