196 Papaya
The damage caused by the virus is usually much greater than the mechanical
injury caused by the insect vector. Bacterial diseases are less frequent but under
high moisture and poor irrigated condition may cause huge damage, namely
Erwinia, Xanthomonas, etc. in papaya.
Fungal diseases constitute one of the biggest groups of foliar pathogens causing
immense damage under protected environment. It was found that the incidence
and severity of diseases vary considerably under protected environment when com-
pared to the open field. As observed in papaya, Phytophthora, Pythium, Fusarium,
Alternaria and Colletotricum were observed to be of higher significance under
polyhouse conditions (Dubey and Singh 2012). This may be attributed to the fact
that temperature and humidity are nearly balanced inside protected structure, even
when outside field temperature is comparatively low and so on. Survival of patho-
gen is also enhanced inside polyhouse due to availability of host because of longer
growing season (Figure 17.3).
17.6.1 Management Strategy
Proper field sanitation is one of the most important management strategies. Since, once
the inoculums build up inside polyhouses it is very difficult to manage it. Incidence
of different diseases was managed by providing ample spacing between plants for
proper air movement and reducing of leaf wetness by avoiding overhead irrigation.
Balance use of chemicals with least toxicity is recommended, especially for poly-
house cultivation. Scout the fields for the first occurrence of virus disease. Pull up and
destroy infected plants, but only after spraying them thoroughly with an insecticide
to kill any insects they may be harbouring. Use reflective mulches to repel insects,
thereby reducing the rate of spread of insect borne viruses. Monitor vector popula-
tion early in the season and apply insecticide treatments when needed. Minimise
plant handling to reduce the amount of virus spread mechanically. Composts have
FIGURE 17.3 Nursery raising under polyhouse.