118 Papaya
mildew in papaya is promoted at high humidity (80%–85%) and a temperature range
of 24–26°C. Infection is first apparent on undersurfaces of leaves as small, slightly
darkened areas, which later become white powdery spots (Rawal 2010). These spots
enlarge and cover the entire leaf area. Severely infected leaves may become chlorotic
and distorted before falling. Fungus may also attack the stem and petioles of young
plants under reduced light. Affected fruits are small in size and malformed. Fungus
takes nutrients from the cells of the leaf surface by haustoria and produces mass of
spores which are carried out by wind from diseased to healthy plants.
10.6.1 Management
In the initial stage of disease, dusting or spraying of sulphur (2.0 g/L of water) at
15 days interval helps to control the disease (Rawal 2010). It may also be controlled
by spraying of Karathen @1.0 mL/L of water (Ram 2005).
10.7 Damping-Off
Damping-off can occur at the pre-emergence stage, in which case seedlings do not
emerge, or post-emergence where seedlings will fall over and die from a constriction
on the stem (often brown) at soil level (Figure 10.6). The tissues of papaya seedling,
arises from soil line, become water-soaked and collapse due to the growth of fungus.
The disease is caused by a complex of fungi viz., P. aphanidermatum, P. palmi-
vora, Rhizoctonia solani and Fusarium sp. (DAIS 2009). Commonly, this disease is
caused by Rhizoctonia. Lesions are seen on the stem at or just above soil level. This
is a soil-borne disease. The stem becomes watery and shrinks, followed by death
of the plant. This disease is aggravated by excessive water or fertiliser, heavy soils,
overcrowding in seedling beds, wet weather and high-humidity conditions (Rawal
2010).
FIGURE 10.6 Post-emergence stage of damping-off in nursery.