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Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

Cabbage Rhizoctonia web blight (126)

Photo 1. Sclerotia of Rhizoctonia on stem and leaves of carrot.

Photo 2. Sclerotia of Rhizoctonia on potato.

Photo 3. Collar rot of tomato caused by Rhizoctonia, showing the cottony growth of the fungus on the stem.

Photo 4. Head rot of cabbage caused by Rhizoctonia.

Summary

Worldwide distribution. Temperate as well as tropical countries. A fungus causes the head rot; it attacks many vegetables and also causes seedling “damping-off”. An important disease.
It survives in soil either living on dying and dead plants or as dormant balls of fungal growth (called "sclerotia") which are splashed onto plants to germinate, infect, and rot the leaves, binding them togethre with cottony fungal growth.
Cultural control: Grow seedlings in either soil-less potting mix, or in pasteurised soil, and clean trays or pots; avoid wounds to plants during cultivation; allow crop remains to decompose completely before replanting; grow root crops in rotation with cabbages.
Chemical control: not recommended.

Common Name

Leaf blight, seedling blight, stem canker, sheath blight, web blight. Usually, the common name is followed by the host, e.g., web blight (of beans), sheath blight (of rice).

Scientific Name

Thanatephorus cucumeris and Ceratobasidium cornigerum are the name of the sexual states, whereas the asexual states are placed in the genera Rhizoctonia and Ceratorhiza, respectively. In this fact sheet, the pathogen is called Rhizoctonia.

AUTHOR Grahame Jackson
Information from CABI (2014) Crop Protection Compendium: Thanatephorus cucumeris (https://www.cabi.org/cpc). Photos 1,2&3 Gerlach WWP (1988) Plant Diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany. Photo 4 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia.

Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.

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