Casava grey leaf spot
Pacific Pests, Pathogens, Weeds & Pesticides
Cassava grey leaf spot (321)
Periconia manihoticola; a previous name is Haplographium manihoticola.
Asia, Africa, South and Central America, Oceania. It is recorded from Fiji, Niue, Papua New Guinea, Solomon Islands, and Vanuatu.
Cassava and rubber (Hevea brasiliensis).
A fungus causing a leaf spot on cassava, somewhat similar to Passalora henningsii (see Fact Sheet no. 95), but affected areas usually larger, somewhat angular and more commonly resulting in withering and death of the leaves. The leaf spots are circular, up to 10 mm diameter, with pale centres and wide brown or purplish borders (Photos 1&2). On rubber, the fungus causes leaf spots and blight of the leaves, petioles (leaf stalks) and twigs.
A disease of minor importance on cassava, but there are reports of it causing leaf spots, blight of leaves, petioles and twigs, and premature leaf drop on rubber. This was reported from Brazil on seedlings of two clones in nurseries as well as plants in the field.
Look for the small spots with pale centres and wide brown/purple margins. Look (using a hand lens or a low power microscope) for the erect stalk-like fungal structures on the spots with groups of spores at the tips (Photo 3).
It is unlikely that disease management is necessary for grey leaf spot on cassava as there have been no reports of yield loss. However, on rubber the disease has been considered severe enough to warrant sprays of mancozeb or chlorothalonil every 7 days.
When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval. Recommendations will vary with the crop and system of cultivation. Expert advice on the most appropriate pesticides to use should always be sought from local agricultural authorities.
AUTHORS Grahame Jackson & Eric McKenzie
Photos 1&2 (taken by Eric McKenzie), and used in this fact sheet, appeared previously in McKenzie E (2013) Periconia manihoticola PaDIL - (http://www.padil.gov.au). Photo 3 Valmir Duarte, Universidade Federal do Rio Grande do Sul, featured on 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.