The plague of the palm trees: signs, symptoms & treatment
Both the red palm weevil and the palm borer, two types of bug that have been killing palm trees across mainland Spain since the 1990s are now present in Menorca.
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Red palm weevil[/caption]
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palm borer caterpillar[/caption]
Red Palm weevil:
The red palm weevil is a variety of flying beetle that is reddish orange in colour measuring up to 5cm in length. It typically affects the Canary palm and the date palm.
Palm borer:
The palm borer is a species of the Lepidoptera family, that is only harmful in the caterpillar stage. It generally affects the date palm, fan palm and Mediterranean dwarf palm although it is recommended to protect all species of palm against infestation.
The weevils and caterpillars are thought to have arrived in Spain inside palm trees that were imported.
[quote] Left untreated, a palm tree infected with red palm weevils or palm borers will die.[/quote]
How they work:
Red palm weevils nest in the crown of palm trees. They spend their entire lifecycle there, as long as there is food to eat. When the food runs out, they fly off to colonise other trees. The beetles tunnel their way into the centre of the tree from the crown, and sometimes reach the base of the trunk. This destabilises and ultimately kills the trees.
Adult moths of the palm borer lay their eggs in the crowns of palm trees between May and November. The eggs hatch within 2–3 weeks and then caterpillars begin to bore their way into the trunk, creating tunnels up to 1.5 metres long, which destroy the palm’s vascular system. If the caterpillar hatches late in the summer, it will remain in the tree through the winter.
Signs and symptoms:
Asymmetrical crown, wilting and falling leaves, holes in the younger leaves, exit holes in the trunk itself, empty chrysalises and an acidic odour are all indications that a tree has been infected.
Unfortunately, by the time these signs become visible the damage is usually already very extensive. So far, no means of early detection has been found.
Prevention:
It is important to only to prune palms in the winter months (December to February). This is because the bugs are attracted to the sap that trees excrete when pruned, and can infect a tree through ‘wounds’ in the trunk.
To protect against infestation, palms should be sprayed with chemical insecticides (clorpirifos 48%, imidacloprid) or nematodes (or a combination of the two) as a preventative measure. This should be done periodically between early spring and late autumn — May to November — usually about five treatments a year are required to prevent infection.
Recommended insecticides are: cloripirifos, imidalcoprid
Recommended nematodes for palm borers: steiernema carpocapsae
Treatments should be carried out by qualified professionals, in accordance with health and safety regulations.
If you have a palm tree that is infected:
- You must inform the authorities. Contact the Area de Agricultura at the Consell Insular. Tel: 971 356 317
- You must carry out an initial ‘shock treatment’, spraying the crown and leaves with chemicals to kill any insects. This is followed 15 days later by a second treatment.
(At present the Consell Insular offers this treatment free of charge for palm trees on private land)
- The affected parts of the tree must then be removed and disposed of, in accordance with government regulations.
