The Coconut Research Station, Veppankulam, has advised farmers engaged in replanting coconut seedlings in areas affected by cyclone Gaja to adopt an integrated approach to check rhinoceros beetle attack in trees.
Rhinoceros beetle is a pest which cuts the leaves of coconut in a ‘V’ shape. Fallen coconut stems kept in heaps in farmers’ gardens and in common sites in villages serve as breeding ground for carry over population of rhinoceros beetles. From there they spread to coconut seedlings posing a threat to coconut farms, said V.G. Mathirajan, Assistant Professor, Coconut Research Station, Veppankulam, in an advisory to farmers.
Coconut trees on 41,492 hectares of the total area of 54,133 hectares in Thanjavur, Thiruvarur, Nagapattinam and Pudukkottai districts were damaged in cyclone Gaja during November 2018, affecting the livelihood of thousands of delta farmers.
With 76% of the total coconut area in the districts damaged due to cyclone, replanting of coconut seedling has been taken up in the affected areas.
Mr. Mathirajan says adult rhino beetles damaged the replanted young seedlings through a unique mode of entry at the collar region, the junction point of seedling stem with soil. Soil bore holes are seen in the collar portion of the coconut seedlings and presence of adult beetle is noticed when the affected collar region is split opened.
““Drying of central shoots are seen in the damaged seedlings and these dried shoots come out when they are pulled out. The extent of damage by rhinoceros beetle in young seedling ranged from 21% to 30%,” he said.
“The foremost management strategy to save the seedlings is removal and burning of coconut stems left in the garden and in the common places to maintain good sanitation,” he added.
The beetle in its various bio-stages should be collected from the manure pits and destroyed. Green muscardine fungus ( Metarrhizium anisopliae ) can be sprayed at the rate of 250 ml with 750 ml water for every cubic meter area of manure pits to check the perpetuation of the pest. As a physical barrier, the young replanted coconut seedlings may be covered with old nylon net used by fishermen to curtail the entry of rhino beetle into the seedlings.
To monitor and mass trap the adult beetles, light traps and pheromone trap (one each for a hectare) can be placed. A mixture of neem seed kernel powder and sand (150 gm/seedling) may be placed in the leaf axils at the rate of 1:2 ratio to keep the beetles at bay. Napthalene balls (12 gm per seedling) may also placed in the central whorl to repel the beetles attacking the young seedling, Mr. Mathirajan suggested.
