SCI-TECH & AGRI

Mite management in coconut

A typical mite damaged coconut

A typical mite damaged coconut  

AN EXOTIC pest, the coconut mite Aceria guerreronis (Eriophyidae : Acari ) infest the surface of tender nuts in typical patches feeding on the whitish meristematic tissues covered by perianth bracts. The third-fifth bunch nuts (post-fertilization) show peak populations that fluctuate unpredictably. The infested area turns brownish with a characteristic pale triangular patch progressing downwards externally. . The nut gets smaller in size and inferior in quality. The external husk becomes very difficult to remove.

Fissures and gummosis may appear on the nuts. Immature nuts may also fall and the yield is 40 per cent less than normal. If the infested nuts are used as seeds, they are very slow to germinate with 10-25 per cent mortality in the nursery bed.

The powdery white mites lay numerous eggs on the nut surface as well as on the inner side of the interior three bracts which cover the nut surface.

A 3-year research on the ecology and management of the pest indicated that the following measures could effectively combat the menace.

The coconut gardens with rich ground vegetation suffer much less damage than those gardens with only coconut palms devoid of cover crops.

Spherical nuts with smaller perianth (less than 2 cm in radius) are much less susceptible to the mite injury. This yardstick will be useful while selecting the mother palms.

Those nuts with deeply clefted perianth are more susceptible to the mite than the nuts with less prominent perianth clefts as evident in Dwarf varieties that are comparatively much less susceptible than Tall and Hybrids which possess bigger and deeply clefted perianth.

Predatory mites are not able to suppress the mite populations.

The fungus Hirsutella thompsoni causes epizootics, wiping out the mites under favourable conditions.

Boron nutrition to the palm in the form of borax (sodium tetraborate) makes the palm resist the mite attack since boron is an essential micronutrient required to strengthen the cells of the growing plant tissues.

Borax can be applied to soil at the rate of 400-600 gram per palm. It is dissolved in water and applied as a drench around the palms. Following the boron nutrition the palms produce more phenols at the mite feeding zones. Thus the infested nuts resist the mite infestation which results in significantly low levels of injury to the tender nuts.

Application of more quantity of organic manures also results in significantly less damage due to the mite since organic manures make boron freely available to the palms.

High dose of potash (4 kg per palm) coupled with the normal dose of borax (200 gram per palm) also lowers the mite attack. Any mechanical injury to the stalk (peduncle or main axis) of the flower bunches causes the nuts to become less suitable for the mites to infest subsequently.

P. M. M. David, S. Thiruselvan, & T. M. Thiyagarajan

AC & RI, Killikulam

Vallanad - 628 252, T.N

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