Fruit rot or koleroga or mahali (Phytophthora arecae ):

The infection and spread of this disease is related directly to the incidence of heavy
rainfall. The disease first makes its appearance just after the first monsoon showers and
extends its stay throughout the monsoon period. A warm damp interval is always very
helpful for its rapid development. It attacks nuts of all ages and if unchecked will extend
to the crown of the plant ultimately bringing about its death.
The first sign of the disease is the appearance of patches of water soaked areas or rotting
tissue at the base of the nuts. The nuts darken and the patches enlarge and they begin to
drop in large numbers. These fallen nuts soon develop a whitish mass all over. If
unchecked, the disease may later invade the crown causing the leaves and bunches to die
within one or two seasons. The disease is carried forward in the remains of infected
materials lying in the gardens from year to year.

Management
 Spray 1% bordeaux mixture in 10 litres of water as  a prophylactic spray just
before the onset of the monsoon.
 Covering the bunches with polythene sheets in the month of June will also control
koleroga to a considerable extent
systemic fungicide  have exellent   protective activity against Phytophthora when spray before monsoon 


systemic fungicides need a minimum of 3 hours on the plant surface before a rain. Contact fungicides are always sensitive to rain but more so prior to drying on plant surfaces.