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Plantwise Technical Factsheet

African palm weevil (Rhynchophorus phoenicis)

Host plants / species affected
Cocos nucifera (coconut)
Elaeis guineensis (African oil palm)
Metroxylon
Phoenix dactylifera (date-palm)
List of symptoms/signs
Fruit  -  odour
Growing point  -  dead heart
Growing point  -  internal feeding; boring
Inflorescence  -  blight; necrosis
Inflorescence  -  lesions; flecking; streaks (not Poaceae)
Leaves  -  abnormal colours
Leaves  -  yellowed or dead
Stems  -  internal feeding
Whole plant  -  internal feeding
Whole plant  -  plant dead; dieback
Whole plant  -  unusual odour
Symptoms
External symptoms are yellowing of foliage, destruction of emerging leaves, and necrosis on flowers. Internal symptoms are mining of the trunks and leaf stems. Affected plant tissue becomes necrotic and decays, emitting an unpleasant and characteristic odour.
Prevention and control

Cultural Control and Sanitary Methods

The primary means of control is preventative, using cultural and sanitary methods. Adult R. phoenicis are attracted to the odour of feeding sites and to damaged palms, in which they lay their eggs. Therefore, the avoidance of wounds is important during plantation management. The passage of a tractor through a young coconut plantation, for example, can lead to serious weevil attack, as the slight damage to the leaf axils caused by tearing as the wheels run over leaves trailing on the ground can open up ideal egg-laying sites. The removal of all heavily attacked and wounded palms, along with those showing distinct growth disorders, discourages further infestations.

Traps made from thinned or wild palms that have been felled and split into longitudinal sections, divert weevils away from cultivated palms, because adults are attracted to the chemicals emitted from damaged wood. Trap heaps are frequently burnt and replaced with fresh trap wood. Older traps can be sprayed with palm sap to maintain their effectiveness. These sanitary methods have been shown to be more effective than insecticides in preventing weevil damage (Anon., 1990).

Combined gas chromatographic (GC) and electroantennographic detection (EAD) studies have been carried out to try and identify the chemicals in freshly felled oil palms that are particularly attractive to male and female adult weevils. A number of compounds stimulated strong antennal responses, including ethyl acetate, ethyl propionate, isobutyl propionate, ethyl butyrate, and ethyl isobutyrate. These volatiles are all characteristic of fermenting oil and coconut palm trees. In addition to enhancing the attractiveness of trap wood, plant volatiles could be used for monitoring purposes, for both sexes of weevil, or to increase the effectiveness of pheromone traps that attract and capture male weevils (see Pheromonal control) (Gries et al., 1994).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
R. phoenicis is a serious pest of palm trees in tropical Africa. Its economic importance is greatest in plantations of oil palms (Elaeis guineensis). It causes similar damage within palm plantations to R. ferrugineus in India and South-East Asia, and R. palmarum in Latin America.

The larvae burrow in the crowns of palms and feed on the shoot and young leaves. They sometimes destroy the growing point, causing the palm tree to die. Leaves turn chlorotic and die. Extensive tunnelling in the trunk weakens the tree, leaving it susceptible to storm damage (Hill, 1983).
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