Casava grey leaf spot

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.

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