116 Papaya
preventing water logging of the soil may control the disease. Soil fumigation is
necessary before replanting papaya in the same field. Application of Trichoderma
viride (15.0 g/plant) mixed in well-decomposed farmyard manure (FYM) should be
applied around the root zone of the plants at the time of planting. The soil should
be drenched with 2–3 L of copper oxychloride (2.5 g/L of water). The application
should be carried out regularly at 15 days interval from the time of planting. During
fruit formation, the plant should be sprayed with the same solution at the same time
interval (Erwin and Ribeiro 1996). Alternately, mancozeb (2.5 g/L of water) may
also be applied. In the case of coller rot/stem rot attack in existing crops, the rotted
portion of the plant should be scraped and copper oxychloride or bordeaux paste
should be applied (Ram 2005). The paste can be prepared by dissolving 1.0 kg of
copper sulphate and 1.0 kg lime separately in 10 L of water each. The two solutions
should be mixed and shaken to form a paste. We have observed that root drenching
with ridomil MZ @ 2.5 g/L of water is also very effective. Phytophthora is effec-
tively managed by application of metalaxyl M + phosphonate (Erwin and Ribeiro
1996). This fungicide is a xylem-translocated compound with an upward movement
in plants in the transpiration stream (Guest et al. 1995). Thus, metalaxyl and related
acylanilide compounds have no effect on root diseases if applied as a foliar spray
because they are not transported to the roots. Phosphonates will not eradicate the
pathogen or eliminate disease, but remain an excellent, cost-effective option for con-
trol of phytophthora diseases (Drenth and Guest 2004).
10.5 Bacterial Wilt
This disease, also known as wilting, chlorosis and necrosis, is caused by the bacteria
Pseudomonas solanacearum and was discovered by E.F. Smith (Seshadri et al. 1977;
Nelson 2012a, b; APS 2014). The incidence of this disease can be severe during the
rainy season and very commonly found in papaya plantation raised in poor-drained
soils. Wilt-like symptoms are very severe in India, especially in Bihar, as growers
wish to abandon their plantations. It is characterised by symptoms viz., yellowing of
upper leaves (Figure 10.4a), followed by death of leaves and subsequent defoliation
(Nelson 2012a, b). The root system was extensively rotted starting first from tertiary
to secondary roots and finally to tap roots (Figure 10.4b). Fruits get shriveled, drop
their unripe fruits gradually, and plant dies within 10–15 days (Figure 10.4c). Further
research for this disease is required.
10.5.1 Management
Generally, papaya is recommended three-year crop rotation and this is to avoid soil
infestation on land previously planted. The crop should be irrigated by adopting the
ring method of irrigation so that the water does not come in direct contact with the
stem. In the case of new plantings, preventing water logging of the soil may control
the disease. Plant refuses/residue from previous plantings should never be incorpo-
rated into the soil. It has been observed that the root drenching with combination of
copper oxychloride (2.0 g/L of water) + streptocycline (0.03 g/L of water) is effec-
tive to recover the plants (Figure 10.5).