Whitefly a growing threat to coconut and other crops

The Whitefly species (Aleyrodidae) is becoming a growing threat to coconut and other agricultural crops in Sri Lanka.

Whiteflies damage plants by sucking out plant juices. Heavily infested plants can be seriously weakened and grow poorly. Leaves often turn yellow, appear dry and drop prematurely. Whiteflies also transmit crop viruses.

Coconut Research Institute (CRI) Deputy Director (Research) Dr. Nayanie Aratchige says that around 1,500 species of the whitefly have been reported from around the world, of which four species, Aleurotrachelus atratus (palm-infesting whitefly), Paraleyrodes minei (citrus nesting whitefly), Aleurodicus disperses (spiraling whitefly) and Aleurodicus cocois (coconut whitefly) are presently a threat to coconut palms in Sri Lanka.

Dr. Aratchige said that the first mention of the whitefly plaguing coconut palms was in Barbados in 1846 and outbreaks have been reported in the Caribbean and South American regions since the 1990s. Outbreaks of rugose spiraling whitefly (Aleurodicus rugioperculatus) have been reported in India since 2016.

The species Aleurodicus dispersus (spiraling whitefly) has been present in Sri Lanka since 1990, but at that time it was considered a minor pest to coconut palms when compared to other crops .

The first major outbreak in coconut plantations in Sri Lanka was reported in 2019 in the Kegalle district and may have been caused by the accidental introduction of a new species via illegal importation of seedlings of the Palmae group, impact of climate change, sudden drop of natural enemy populations of the native population of whiteflies due to excessive use of insecticides on other crops.

Dr. Aratchige said that Whiteflies have invaded coconut plantations in the Gampaha, Kegalle, Kandy, Kalutara, Colombo, Kurunegala, Ratnapura, Puttalam and even the Galle, Matara and Hambantota districts which have been battling the Weligama Coconut Leaf Wilt disease for over a decade.

Banana, guava, citrus fruits, avocado, eggplant, okra, cashew, Indian almond (kottamba), kithul palm, areca nut, ornamental plants, curry leaves, green chilli, mango, jackfruit, breadfruit, neem, pigeon pea, different varieties of pepper, water melon, coffee, etc., host the whitefly.

The CRI and the Coconut Cultivation Board are conducting awareness programmes on identification of the pest and coordinated spraying of insecticides.

Dr. Aratchige said that placing yellow sticky traps or spraying insecticides to control the menace is recommended. Neem oil and soap mixture is recommended for all infested areas as this mixture is less toxic to the natural enemies of whiteflies. Artificial insecticides are particularly recommended for newly infested areas and the coconut seedling nurseries.

The CRI is researching on methods of chemical and biological control and have sought assistance from other countries for importation of exotic natural enemies of the whitefly.