Scab

Causal organism: Fungus

Host plants

Mango, sweet potato

Affected plant stages

All growth stages

Affected plant parts

Stems and leaves

Symptoms

Mango scab (Elsinoe mangiferae)

Attacked leaves have dark-brown to black circular and somewhat angular lesions. As the lesions enlarge, they become white to gray with narrow and dark margins. Attacked stems have grayish and irregular blotches. Infected fruit's skin has blemishes. The early infection appears as grayish-brown lesions with irregular margins. As the disease develops, it causes cracked and corky appearance. Even if the disease is only found on the skin, the numerous spots lessen the appeal of the consumers.

Sweet potato scab (Sphaceloma batatas)

Small brown lesions are found on the veins of the leaves. As the disease progresses, these lesions become corky that caused the leaves to curl. The stem lesions are slightly raised with rusty-brown spots. Scab-like structures form on the stems as the spots meet.

Preventive control

Hot water treatment for mango

Dipping newly harvested fruits in hot water (53°C for 5-10 minutes) minimizes anthracnose and stem-end rot infestations. Anthracnose will be reduced by 83% and stem-end rot by 100%.

To facilitate heat water treatment, you need dipping tank, thermometer, and wire baskets. The water should have a uniform temperature within the tank to be effective. After dipping the fruits in hot water, dip them in tap water to about two hours or place them in a well ventilated room to cool down.

For sweet potato, proper selection of planting materials and there are now new cultivars that are found to be resistant to the disease.

References

• PCARRD. (1988): Cebu Techoguide: Mango. Philippine Council for Agriculture and Resources Research and Development and Central Visayas Technology Packing Project, Philippines.
• Ploetz, R.; et. al. Editors. (1998): Compendium of tropical fruit diseases. APS Press, The American Phytopathological Society. Saint Paul, Minnesota, USA.
• Thurston, D. (1998): Tropical plant diseases. Second Edition. APS Press. The American Phytopathological Society. St. Paul, Minnesota, USA.