Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Yam anthracnose & dieback (016)

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Photo 1. Leaf spots of Colletotrichum gloeosporioides with typical yellow margins (haloes), expanding, and in some cases developing into a severe blight resulting in early death of the leaves.

Photo 2. Only leaf veins of some yam varieties are infected by Colletotrichum gloeosporioides, and this happens when the leaves are young. As the leaves expand the damage causes them to become boat-shaped.

Photo 3. Leaves blacken rapidly after lengthy periods of rain followed by sunny days. Blackening occurs on the leaves and also on the stems in response to spores of Colletotrichum gloeosporioides. The spores germinate but do not infect.

Summary

• Worldwide distribution. There are many strains of the fungus attacking crops and weeds. An important disease.
• A wet weather fungus mainly on greater yam. Spots on young leaves expand rapidly causing them to fall early. Shoots die back, and old leaves turn black. New shoots grow from the sett, but if they become infected, these die back, too. Often, there are no tubers, or just many small ones.
• Spread occurs when spores are moved in wind-driven rain and, perhaps, long distance in planting setts.
• Cultural control: plant early ahead of rainy season; check setts for rot; interplant with maize; do not weed when plants are wet; collect and burn trash after harvest; resistant varieties; 3-year crop rotation.
• Chemical control: copper, chlorothalonil, or mancozeb.

Common Name

Yam dieback, yam anthracnose, lightening disease of yam

Scientific Name

Glomerella cingulata (it also has the name of Colletotrichum gloeosporioides). Glomerella is the sexual state of the fungus.

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