Diseases 121
Infection on these petioles is important since they may act as a source of inoculum
for infection of fruit. The trunk also gets scorched on the side exposed to sun and
develops sunken area on its bark which gets dry and fibrous, causing the plants to
collapse during the summer season.
10.9.2 Management
The affected fruits should be removed and destroyed properly. The fruits should be
harvested as soon as they mature. Since the disease is associated with scorching sun,
shading the fruits and trunk is a preventing measure. Closer planting and frequent
irrigations may reduce this malady. Ammonium carbonate (3.0%) incorporated into
the wax formulation effectively reduced anthracnose incidence by 70% in naturally
infected papaya and extended the storage life by maintaining the firmness, color
and overall quality of the fruit in low temperature storage (13.5°C) and 95% R.H.
for 21 days, followed by 2 days, under marketing conditions (Shiva Kumar et al.
2002). It can also be controlled by propiconazol (Sepiah 1993), double dip hot water
treatment and hot water dip treatment at 43–49°C for 20 min with combination of
fungicide (Couey et al. 1984). However, hot drip water treatment also affects the
ripening process (Paull 1990). Sodium bicarbonate (2%) significantly reduced the
disease incidence and severity up to 60% during storage in papaya (Hasan et al.
2012). In the initial stage of this disease, it can also be controlled by spraying with
mancozeb (1.0 g/L of water) or carbendazim (1.0 g/L of water) or thiophanate methyl
(1.0 g/L of water) at 15 days interval (NHB 2002).
10.10 Leaf Blight
The disease is caused by Corynespora cassiicola and severely damages the leaves. The
disease first appears as small, discoloured lesions, which are irregularly scattered on the
leaves. These spots become irregular in shape, then increase in size and appear brown
to grey in colour. A light yellow zone surrounds the spots. Several lesions coalesce to
cover large areas of the leaf and in severe infections; the whole leaf dies (Figure 10.9).
A considerable reduction in the yield is observed. It can be controlled by spraying of
mancozeb (2.0 g/L of water) starting from the appearance of the disease symptoms.
10.11 Phytophthora Blight
Phytophthora blight has also been called soft foot rot, stem canker, soft fruit rot
and root rot. The pathogen, P. palmivora was named in 1919 by E.J. Butler. It was
once classified as a fungus, but now it is regarded as a pseudo fungus in the stra-
menopiles. It is caused by a fungus (Phytophthora parasitica) and major disease in
high-rainfall areas and wet weather. Young fruits are affected by this disease with
water-soaked lesions exuding milky latex. Fruit rot initially appears as small, circu-
lar water-soaked lesions about 5–10 mm in diameter. Large lesions, often forming
first where the fruit contacts the stem of the plant, are covered with whitish myce-
lium and masses of Phytophthora sporangia (Erwin and Ribeiro 1996). Fruits can
rot, turn soft and fall prematurely and mummify. The top portion of the fruit-bearing