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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

Pham NQ, Wingfield MJ, Duong TA, Wingfield BD. (2026) Draft genome sequence of Elsinoe masingae: the causal agent of Eucalyptus scab in South Africa. Australasian Plant Pathology 55:37. 10.1007/s13313-026-01082-5
Pham NQ, Marincowitz S, Wingfield BD, Crous PW, Santos SA, Durán A, Tarigan M, Wingfield MJ . (2026) Pseudoteratosphaeria supramediana sp. nov. (Teratosphaeriaceae, Mycosphaerellales), a new foliar pathogen on Eucalyptus in Indonesia. Australasian Plant Pathology 55:28. 10.1007/s13313-026-01092-3
Nel WJ, Jali S, Barnes I, Wondafrash M, Hurley BP. (2026) Outbreaks of a native jewel beetle, Agrilus grandis (Coleoptera: Buprestidae), on commercial black wattle, Acacia mearnsii, plantations in South Africa. African Entomology 34(1):1-5. 10.17159/2254-8854/2026/a24625
Postma A, Klynsmith L, Duong TA, Allison JD, Smidt W, Waterhouse RM, Lesny P, Oeyen JP, Petersen M, Martin S, Liu S, Zhou X, Ziesmann T, Donath A, Mayer C, Misof B, Niehuis O, Peters RS, Podsiadlowski L, Coetzee MPA, Joubert F, Slippers B. (2026) Genome and transcriptome-based identification and expression profiling of chemosensory gene families across developmental stages and tissues in Sirex noctilio (Hymenoptera: Siricidae). Insect Molecular Biology :1-14. 10.1111/imb.70029
Aylward J, Visagie CM, Roets F, Wingfield BD, Wingfield MJ. (2026) Genome analyses reveal two novel species of Seiridium from Acacia mearnsii. Mycological Progress 25:8. 10.1007/s11557-026-02121-7