Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Yam leaf spot (312)

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Photo 1. Typical infection on mature leaves of Dioscorea esculenta by leaf spots of Guignardia dioscoreae.

Photo 2. Yam leaf spots of Guignardia dioscoreae on Dioscorea esculenta, tan with darker margins.

Photo 3. Yam leaf spots, Guignardia dioscorea, on Dioscorea pentaphylla.

Summary

• Widespread distribution. On all yam species, but most common on asiatic yam (or lesser yam), Dioscorea esculenta. A minor disease, unlikely to effect yield.
• Leaf spots, circular or irregular, up to 10 mm diameter, tan or grey, merging, with dark brown or black borders. Fruitbodies can be seen as black pin points in the spots.
• Spread occurs when spores ooze from fruitbodies during wet weather and splashed by rain or carried by wind.
• Cultural control: collect debris (vines and leaves) and destroy after harvest; 2-3 year crop rotations; test varieties for differences in tolerance.
• Chemical control: unlikely to be needed, but if requuired use chlorothalonil, copper, or mancozeb.

Common Name

Yam leaf spot

Scientific Name

Guignardia dioscoreae. Previously known as Guignardia dioscoreae-bulbiferae and Phyllostricta dioscoreae. Guignaria is the sexual state, and Phyllosticta dioscoreae is the asexual state, i.e., spores are produced without mating strains combining.

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