Diseases 115
the petioles are twisted. In severe cases, complete defoliation of the affected plant
is observed. The affected plants show a stunted growth with reduced fruit yield and
quality (Ram 2005).
10.2.1 Management
Practically, there is no control measure for this virus. Removal (rouging) and
destruction of the affected plants is the only control measure to reduce the spread of
the disease. It can also be minimised by planting the crop after rainy season (Ram
1984a, b). Checking the population of whitefly can also reduce the infection severity.
Application of dimethoate (0.05%) or metasystox (0.02%) at an interval of 10 days
effectively controls the whitefly population (NHB 2002). Addition of heavy doses of
organic matter results in lesser disease incidence as compared to the application of
chemical fertilisers.
10.3 Papaya Apical Necrosis
Papaya apical necrosis is a relatively new virus. Symptoms include a drooping and
downward cupping of the leaves, reduced leaf size and browning of the leaf margins.
At present, there is no control for this disease.
10.4 Collar Rot or Foot Rot
This disease is caused by soil-borne fungi namely Pythium aphanidermatum and
Phytophthora palmivora (Guadalupe 1981). The oospores are formed on the papaya
residue in soil. The pathogen can survive on dead organic matters as saprophyte
and causes infection when suitable host is grown in such soil. The secondary spread
takes place by zoospores. This disease is widely spread in papaya plantations of
India, Sri Lanka, Hawaii and South Africa. Under favourable conditions of high rain
fall and high temperature, the whole plantation is wiped out within one season. The
incidence of this disease would be severe during rainy season and commonly found
in poor-drained soils (Erwin and Ribeiro 1996). It is characterised by the appearance
of water-soaked patches on the stem near the ground level. These patches enlarge
rapidly and girdle the stem, causing rotting of the tissues, which then turn dark
brown or black. Such affected plants cannot withstand strong wind and topple over
and die. If the disease attack is mild, only one side of the stem rots and the plants
remain stunted. Fruits are shriveled, malformed and gradually the plant dies. Trunk
rot (P. ultimum) is damaging to papaya in USA, Africa and India. It is also known as
collar rot in 8–10 months old seedlings, evidenced by stunting, leaf-yellowing, shed-
ding and total loss of roots (Koffi et al. 2010).
10.4.1 Management
Papaya is, generally, not recommended on land previously planted and this is due to
soil infestation by P. aphanidermatum and P. palmivora. Plant refuses from previ-
ous plantings should never be incorporated into the soil. In the case of new plantings,