Pacific Pests, Pathogens and Weeds - Online edition

Pacific Pests, Pathogens, Weeds & Pesticides

Bean Pythium cottony leak (128)

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Photo 1. Pythium sp. causing cottony leak disease on a bean pod. Note that the white cottony growth on the lower part of the pod is the mycelium of the water mould (it is not a fungus).

Photo 2. Cottony leak fungus, Pythium sp., developing on stored beans. The water mould develops in storage if the beans are not dried properly after harvest and/or they have been damaged.

Photo 3. Pythium sp. causing cottony leak disease on a cucumber fruit. Note that the white patch on the lower left of the fruit is the mycelium of the water mould (it is not a fungus).

Summary
  • Worldwide distribution. On beans, capsicum, cucumber, tomato, and causes damping off (see Fact Sheet no. 47).
  • Grey patches on leaves; fungal growth spreading to stems causing wilts; thick cottony growth rots pods in field and storage. Cucumber touching the soil rot.
  • Usually a minor disease, except during long rains.
  • Cultural control: allow air movement; avoid wounds; stake beans and cucumbers; improve drainage; use mulch; rotate with e.g., root crops; avoid harvesting in wet weather; for damping off (see fact sheet).
  • Chemical control: treat seed with fungicides: captan, matalaxyl or thiram; damping-off (see FS above).
Common Name

Cottony leak and stem rot. It is also known as Pythium fruit rot or Pythium cottony leak.

Scientific Name

Pythium species, Pythium deliense and Pythium aphanidermatum.

Photo 4. Cottony leak, Pythium sp., on watermelon.

AUTHOR Grahame Jackson
Information (and Photo 2) Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, et al. CSIRO Publishing; and from (including Photos 1&3) Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany; and from Melanson RA (undated) Cottony leak in cucurbits. Mississippi State University. (https://extension.msstate.edu/sites/default/files/publications/publications/P3210_web.pdf). Photo 4 Jacquie (Wright) Kami, formerly Plant Pathologist, Secretariat of the Pacific Community, Suva, Fiji.

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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