Controlling coconut root grub
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The beetles are nocturnal in nature
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ROOT GRUB has become a serious pest of coconut mainly in the states of Kerala and Karnataka.
Many of the intercrops in coconut such as cassava, nutmeg, clove, cocoa, colocasia and vegetables, are prone to root grub attack.
Damage to intercrops
Intercrops cultivated during September and February suffer severe damage since this period coincides with the heavy feeding third instar stage of the grubs.
The pest is a chestnut brown coloured beetle. The longevity of both sexes is around 42 days. Eggs laid in soil are white in colour and vary from 30 to120 in number.
On onset of the pre-monsoon showers, the beetles emerge in large numbers in the evening hours thus acquiring the name May-June beetles.
Visible symptoms
Leaf yellowing, delayed flowering and immature nut shedding are the visible symptoms of this pest damage on coconut. Changes in cropping pattern, cultivation practices, reduction of natural predators such as birds, beneficial microflora and fauna in soil aggravate the pest damage.
Mechanical control includes tilling and deep ploughing to expose the grubs to natural predation or desiccation under sunlight.
Application of karanj (Pongamia glabra) oil cake at 2000 kg per hectare, neem oil cake, growing bandhi (Tagetus erectus) flower plants as a repellent crop, setting up of light trap for collection of adults seem to reduce the severity of damage.
Pest control
Two applications of phorate at 10g per palm during May-June and September-October effectively control the pest.
Harvesting of coconut should be done after 45 days in case of pesticides use.
Drenching (0.04 per cent) chlorpyriphos at 2 ml per litre of water is also found effective. Digging the field exposes the grubs.
Bindu T.N.
& Filitte Stephen
College of Agriculture, Padannakkad
Kasaragod, Kerala
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