Palm weevils have become a major garden menace
During the past ten years the Palm weevil or beetle has destroyed thousands of palm trees in Spain and other Mediterranean countries. In this article we discuss the phenomenon.
Other names for the Palm Weevil
The scientific name is Phynchoporus ferrugineos, the Spanish name is Picuda roja and there are a variety of English names such as Palm weevil, Red palm weevil, Red palm beetle, Palm worm (the larvae) and Giant palm weevil. There are many others in different languages around the world.
Origins of the Palm Weevil
Apparently the main origin was Indonesia and Polynesian islands where their natural predators help to keep the weevil under control. Movement across the world has been by weevils hiding in exported goods and larvae in already infected palms.
How fast has the weevil attacked the world?
The major invasion of Spain started in 1994 apparently in diseased palms imported from Egypt. Other invasions include Saudi Arabia 1985, Portrugal 1996, France 2004, Canary islands 2005,Balearics 2006, Malta 2006, Italy 2006, Greece 2006 and California 2010. Imported trees from Asia have apparently accelerated the problem in a number of these countries.
The life cycle of the palm weevil
One weevil can lay around 200 eggs every ten weeks, and these produce larvae which become mature weevils after seven to ten weeks. That’s a lot of new weevils in a year!
The grub like larvae eat the inside of a palm tree for around a month before exiting from the trunk through a small tunnel to form a cocoon at the base of the tree before transforming into an adult beetle. At first it crawls but once dried out in the sun, as a butterfly does, it is said to fly up to five kilometres!
How to detect palm weevils & beetle in your palm trees?
There are several ways to detect the palm beetle and its larvae. Look for crawling weevils around the base of a palm. You can see them in the leaves if stood on a ladder. You can actually hear the crunching noise of the eating grubs through the bark of the trunk of the tree.
Look for chewed wood and a viscous smelly liquid coming out of holes. There is a fermenting smell in the area of a palm tree and of course dying fronds on top of the trunk.
Controlling & Curing the Palm Weevil
Naturally this depends on how early in the life cycle you notice the problem. If you sprayed or injected insecticides into the trunk as soon as a weevil has just laid eggs or the eggs just hatched out as small grubs you would have a chance of curing the problem.
But if you can hear grubs through the trunk it depends how much of the soft core of the trunk has been eaten. Two or three hundred grubs each eating and chewing a tunnel up to a metre long will soon take a palm tree beyond the point of no return as the palm will not be able to draw up and transport moisture and nutrients from the roots to the crown of the palm.
This situation can be reached before there are any signs of dying fronds at the top of the palm. For instance two palms have fallen over in a neighbours garden in the past month. The centre was well hollowed out and full of growing grubs but luckily still needing a couple of weeks to be large enough to become chrysalises.
On the other hand there is a palm in the garden of a neighbouring unoccupied house with fifty percent of the fronds dead and others on the way. Although taller, the palm is still standing. Naturally such a situation can only lead to a further spread of the pest.
What Insecticides can be Used to control Palm Weevil and When to Use?
The general message is that preventive spraying or injections is best done eight times a year, especially in the spring and autumn. Once a palm is affected killing the larvae is important to stop adult weevils developing and spreading the disaster.
The latest communication from our town hall is that Chlorpiritos 48%, Imidacloprid 20% and Tiametoxan are approved for village parks and gardens and domestic gardens. These are either sprayed over the crown and trunk or injected into the trunk.
Jeyes fluid and neem oil are also being used.
Apparently Malta and Cyprus have obtained EU grants under a plant health programme to help eradicate the weevils but we have so far not been able to identify what method of control is being used there.
What should be done with dead palms?
When the tree is cut or falls down cut into lengths and immediately drown visible grubs. Next treat all cut ends and top and bottom of the tree with one of the previously mentioned insecticidal products.
Then wrap up each length in plastic and bag up the fronds from the crown of the palm and contact the local authorities to arrange for the palms to be transported away for incineration.
Note that dragging the fronds around or tying them in bunches and leaving at the gate to await a weekly garden rubbish collection could lead to the distribution of eggs and small grubs.
What Types of Palms are Affected by Weevils?
In the main it is the Canary Island palm ( phoenix canariensis)and the coco palm(phoenix dactylifera) but there are cases of Washingtonias and others also being affected. It has been suggested that if weevils run out of their favourite palms to eat they will move onto other palms to survive. To date dwarf native palms Chamaerops humilis have not been reported as being affected.
Recently planted and badly pruned palms are at most risk.
The Way Ahead
We can only suggest to readers that they are doubly alert to the risk to their palms and take precautionary preventive actions using qualified licensed persons. Move fast if problems are observed and plant no further palms in their gardens.
As with the loss of geraniums through the geranium moth the Spanish and other Mediterranean scenery will be less interesting but at least there are many alternative plants including tropical looking cotyledons, to plant up.