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Pacific Pests & Pathogens - Mini Fact Sheet Edition

Taro minor leaf spots (094)

Photo 1. Early symptoms, brown or ghost leaf spot, Cladosporium colocasiae; some spots show a faint darker border.

Photo 2. Older leaf with brown leaf spot, Cladosporium colocasiae.

Photo 3. Underside of the leaf with orange leaf spot, Neojohnstonia colocasiae; spores develop in the spot on the underside of leaves.

Photo 4. Upper surface of leaf with orange leaf spot, Neojohnstonia colocasiae (matching Photo 3); spores develop in the spot on the underside of leaves.

Photo 5. Older leaf with orange leaf spot, Neojohnstonia colocasiae.

Photo 6. White leaf spot, Pseudocercospora colocasiae, on upper surface of taro leaf.

Photo 7. White leaf spot, Pseudocercospora colocasiae, on upper surface of taro leaf.

Photo 8. White leaf spot, Pseudocercospora colocasiae, on lower surface of taro leaf.

Photo 9. Shot-hole, Phoma sp., showing large oval spots with yellow halos, some with holes where the centres of the spots have fallen out.

Summary

Widespread distribution. Asia, Southeast Asia, Oceania. Ghost spot has probably the widest distribution, and is likely to be present wherever the crop is grown. On taro. Minor diseases.
Ghost leaf spot (Cladosporium), orange leaf spot (Neojohnstonia), white leaf spot(Pseudocercospora) and shot-hole (Phoma). On older leaves.
Ghost – reddish-brown with light brown centres, not all penetrating to the undersurface; orange – yellow-brown, sometimes with yellow border; white – whitish-green, dark centres below, leaving white margin; shot-hole – brown up to 20 mm (larger than others), centres fall out leaving hole with yellow halo. All are spread in wind and rain.
Cultural control: none recommended, as the spots are unlikely to affect yields.
Chemical control: none recommended.

Common Name

Brown or ghost leaf spot, orange leaf spot, white leaf spot and shot-hole

Scientific Name

Cladosporium colocasiae (brown or ghost leaf spot), Neojohnstonia colocasiae (orange leaf spot), Pseudocercospora colocasiae (white leaf spot), Phoma sp.(shot-hole). Phoma sp. is often given as Phyllosticta colocasiicola.

AUTHORS Helen Tsatsia & Grahame Jackson
Photos 2,5&6 (Gerlach WWP (1988) Plant diseases of Western Samoa. Samoan German Crop Protection Project, Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) Gmbh, Germany. Photos 3&4 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Neojohnstonia colocasiae. PaDIL - (http://www.padil.gov.au). Photo 6-8 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Pseudocercospora colocasiae. PaDIL - (http://www.padil.gov.au).

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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