We are passionate about plants!
The March of the Palm Beetle, part 2.
Last week I gave you some of the history of the palm beetle in Spain, its coverage and range. This week, we need to learn how to identify the foe and deal with it!
The beetle is a rusty red/brown colour, hence the name, up to 5 cm long and 1.2 cm wide – so he is really quite an unmistakeable fellow! They have a ‘beak’ on the headpiece, hence picudo in Spanish, which, in the male beetle, is hairy. The eggs are creamy white and look very similar to a grain of rice. The female will lay where the leaf joins the trunk, or in any trunk fissure and sometimes, most devastatingly, in the crown of the tree. Around 500 eggs will be laid in one batch and it is the ivory coloured grub-like larvae which cause all the damage, devouring the crown or heart of the tree and tunnelling metre long channels down into the trunk of the palm. They live two to three months then pupate, wrapping themselves in palm fibre. Thus, four generations can be incubated each year, especially in warm conditions. The adults can fly up to 5 km, moving on when they sense the tree is dying. They search for weaker trees to invade – either those that are newly planted or have been badly/over pruned. With those sorts of figures, it’s easy to see how the plague has spread so quickly.
The first signs of damage will be an abnormal yellowing of the leaves, especially those held higher in the crown. It is quite normal for the lower, ageing palm leaves to yellow and dry off. But infestation is much more dramatic; the leaves will twist and distort, fading to a straw colour and the entire crown of the tree will start to collapse. An infested leaf, may show reddish deposits where it joins the trunk – this is a sure indicator. A tip – LISTEN to your palm; the noise of the voracious grubs is quite audible. Once the tree is badly infested it will give off a putrid smell as the inner tissues decompose. Sadly, often, by the time the damage is noticed, it’s generally too late to take any effective measures and the tree will have to be destroyed.
If you suspect your palm tree is infested, contact your local Town Hall: most are now offering free surgery and disposal. The authorities are keeping records of the path and spread of the infestation. They will send out someone to inspect the tree. If necessary, it will be cut down, bagged up and cleared away. Never try to tackle the problem by yourself; burning the tree worsens the situation because the beetles take off for new pastures!
More positively, let’s look at preventative measures that are available to us. Firstly, strong healthy trees are less at risk. Feed and water your palms (moderately) during the summer months to keep the sap flowing well. A regular course of treatment with neem oil, an organic product, (which I’ll cover in a later article) deters the beetles. Keep your palm trees clean and tidy, but never over-prune: a palm tree should always have a large head of leaves, arching gently over. Green leaves produce food for your palm so never be over-zealous when pruning.
For several years now, local authorities have been carrying out spraying programmes, especially on urbanisations and civic plantings, but, obviously, solitary palms are often missed and, it now seems, the spraying has not been fully effective, (as the larvae are deep within the trunk) though it has offered some form of control. Current measures include injecting the trunks with 4-metil or 5-nonanol, but this is a specialist procedure.
Some of the most interesting research is going on in Israel, where specially trained sniffer dogs can isolate affec ted palms and these can either be treated or destroyed before wide-scale invasion. And, it seems that palm trees, and especially weakened ones, give off a special chemical scent, known as a pheromone, which acts as a signal attracting the beetle. Hence pheromone traps can be set to lure in the beetles and they can then be destroyed – on the same lines as a beer trap for slugs. Natural predators would be another solution, but the introduction of these could lead us into a whole new set of problems! However, these non-chemical approaches must, surely, be the way forward and are far more inviting than spraying with a cocktail of chemicals, probably causing death to a lot more than just the palm beetle!