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Scab

Causal organism: Fungus

Host plants

Mango, sweet potato, potato

Affected plant stages

All growth stages

Affected plant parts

Stems, leaves, and tubers

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.

nPotato scab (Streptomyces scabies)

Reddish-brown spots appear on the surface of the developing tubers during the early infection. The spots are circular which coalesce into large scabby areas. The tissues become corky and warty with shallow to deep holes and are necrotic as the infection progresses.

Sweet potato scab (Elsinoe batatas, 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 (53C 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 potato scab, practice crop rotation (rye, soybean, alfalfa, corn and small grains are good rotation crops); avoid carrots, beets, red clover and radish as rotation crops; plant resistant varieties; provide enough soil moisture during the tuber formation; and maintain the soil pH level between 5 -5.2.

For sweet potato scab, proper selection of planting materials, crop rotation with small grains and corn, and practice field sanitation. There are now new sweet potato cultivars that are found to be resistant to the disease.



External links


References


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