If you’re wondering why the P-O is graced with fewer palms than a decade ago or why many remaining trees look sick or dead, pests in the form of a moth and weevil are to blame.

Lesley McLaren explains.

THE CULPRITS

Palm moth (Le Papillon du palmier)

Accidentally imported in palms from South America, they’re big and easy to spot when flying – from early May to end November.

Pretty on top

Less pretty underneath

That heavy body makes them inelegant flyers. And hard to squash.

September – November is egg-laying season – on palm trunks. Larvae fatten into white caterpillars. At 6-7cm long, they look like giant maggots.

This is a mature grub. It’s these, not the moths, that cause the devastation.

Red Palm Weevil (le charançon rouge des palmiers)

Originating in Asia, both the beetle and larvae eat palm leaves and burrow into their stalk bases.

Adult

 

The moths and adult weevils are attracted from a distance by the smell of sap from cut fronds or wounds on trunks and, because neither pest has natural predators in this part of the world, they lay waste to our palms (but only those plants) with gay abandon.

THE DEVASTATION

All varieties are susceptible. Once infested, they quickly sicken.

One summer yours looks healthy …

Next spring, the lower fronds are weak, creating a two-tiered effect.

Only a month later, it’s lopsided. The end is nigh.

In other cases, all fronds rapidly turn grey and die.

And some simply topple over because the trunk has been fatally weakened.

SYMPTOMS

  • Put your ear to the trunk in winter, and you might hear chomping.
  • Sections of chewed out leaves.
  • Holes in the crown or trunk, from which chewed-up fibres are ejected (resembling sawdust).
  • A withered crown or bud.

PREVENTION

No method guarantees success.

  • Prune in winter or early spring, when the insects aren’t flying.
  • Apply a special type of glue to the bark, to prevent moths from laying eggs. Practically challenging, with dubious efficacy?
  • Enclose the palm in netting from May to December. Not an attractive look, even if it works!

ONCE INFESTED, IS THERE A CURE?

No, but you can wage permanent war.

  • Pesticides are forbidden for private palm owners, but …
  • Your weapon is a species of nematode, Steinernema carpocapsae (available via the Internet). These 0.1mm long roundworms burrow into larvae and discharge a bacterium that will kill them within a few days. But nematodes’ natural habitat is soil, and they’re delicate little critters, so this isn’t quite as simple as it sounds …

TIPS FOR NEMATODES

  • Apply to the palm crown, where most larvae congregate.
  • Apply at dawn, dusk or when the sky is overcast! They can’t stand sunlight.
  • Repeat at least each season, because they die off in winter and are inactive below 12 degrees C. Ideal air temperature is 15-20 degrees.
  • Oh, and in the 6-8 weeks following application, keep the palm crown damp.

If all is lost, palms should be felled – ideally over winter, before the next generation of adults emerges. It should be done by an accredited tree surgeon or gardener. Expensive? Yes, but it ensures correct disposal of the plant and any insects or larvae within it. (Sadly, all too often palm remains are dumped in the countryside, which only helps spread the pests further.)

So you’ve had your palm chopped down. You’ve done the right thing and you’re no longer spreading infestation through the neighbourhood, right? Well … Ours was cut to within a couple of centimetres of the ground. Three years later, one day in April, I took a pickaxe to the stump (as you do), and unearthed eight mature moth caterpillars feasting on the root ball.

They hadn’t been there all the time – it means the moths lay eggs on stumps!

Here’s a link to a short video of the grub in action. And you can watch a palm moth laying eggs, here.

Lesley McLaren

   Lesley is one of the “Warblers” – a small group of natural history enthusiasts based in the P-O. Their blogs and photos can be found at Mediterranean Pyrenees

All photos in this article are by The Warblers, unless otherwise stated.

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