Palms of all age are liable to be attacked but normally young palms are more susceptible, particularly during monsoon when the temperature is low and humidity is very high. In seedlings, the spear leaf turns pale and comes off with a gentle pull. The earlier symptom is the yellowing of one or two younger leaves. Black spots appear on spindle leaves. Basal tissues of the leaf rot quickly and can be easily separated from the crown. Infection spreads to the older leaves, causing sunken leaf spots covering the entire leaf blade. Spot margins are irregular and water soaked, and when the leaves are unfolded the characteristic irregular spots are conspicuous on the blade. In the later stages the spindle withers and drops down. The tender leaf base and soft tissues of the crown rot into a slimy mass of decayed material emitting foul smell. Ultimately the entire crown falls down and the palm dies.
In early stages of the disease, when the spindle leaf starts withering, cut and remove all affected tissues of the crown along with some healthy tissues and apply Bordeaux paste and protect it from rain by providing a mud pot or a polythene covering till normal shoots emerges.
- Spray 1% Bordeaux mixture to the spindle leaves and 2-3 innermost whorls of leaves.
- Burn all diseased tissues removed from the palm.
- As a prophylactic measure, spray 1% Bordeaux mixture on the spindle leaves and on the base of 3-4 innermost whorls of leaves of neighboring palms.
- In palms that are sensitive to copper containing fungicides, spray and spray drench with Mancozeb 0.4% (4g/L).
- Small perforated sachets containing 2g Mancozeb may be tied to the top of the leaf axil. When it rains, a small quantity of the fungicide is released from the sachets to the leaf base, thus protecting the palm.
- Adopt control measures for rhinoceros beetle and red palm weevil.
- Provide adequate drainage in gardens.
- Adopt proper spacing and avoid overcrowding in bud rot prone gardens.
- In bud rot prone gardens, prophylactic measures should be done to all palms 2-3 times at 45 days intervals.
- Clean the crown before monsoon and follow strict phyto-sanitation.
- Regular application of organic matters favors the establishment of bio-control agents and suppression of pathogens.
- Apply salt and ash mixture or paddy husk after removing the affected portion in the crown and subsequently cover with a mud pot. They absorb moisture and keep the protected portion dry.
- Apply bleaching powder on the affected portion.
- Cut and remove badly affected palms from the field.
Stem bleeding is characterized by the exudation of a dark reddish brown liquid from the longitudinal cracks in the bark and wounds on the stem trickling down for a distance of several inches to several feet. The lesions spread upwards as the disease progresses. The liquid oozing out dries up and turns black. The tissues below the lesions become rotten and turn yellow first and later black. In advanced cases, the interior of affected trunks are hollow due to decay of interior tissues. As a result of extensive damage in the stem tissue, the outer whorl of the leaves turn yellow, dry and shed prematurely. The production of bunches is affected adversely. Nut fall is also noticed. The trunk gradually tapers at the apex and crown size becomes reduced in chronic cases.
For early infections, chisel or scrape out the rotten portion. Treat wounded or infected areas with fungicide and tar (for example, Bordeaux paste, mancozeb, or copper oxychloride), followed by sealing with coal tar two days later. Burn or destroy the chiseled pieces. Apply neem cake to the base of affected plants. Advanced symptoms may be virtually untreatable, requiring palm removal and destruction. Weakened coconut palms with rotting stems may be a toppling hazard in high winds.