Brace yourself for the new invasive pests, from to oak-munching caterpillars to Asiatic hornets

Charles Quest-Ritson takes aim at the foreign invaders who seem set to ravage our gardens.

The RHS informs us that ‘the arrival of new pests and diseases in the UK is linked to the rise in the volume and diversity of plants being imported’. I am therefore pleased to report that I’ve done my bit to limit that ‘volume and diversity’.

Last year, an Italian friend gave me a very pretty oleander (pink, double-flowered and sweetly scented), which I brought back to England in the boot of the car, alongside quantities of wine and olive oil. Only after I’d grown it at home for a while did I notice a massive colony of scale insects happily hugging its stems.

There are thousands of species of scale insect and one can co-exist with most of them without fear of the consequences, but some are serious parasites of economic crops such as citrus fruit. Suddenly, I was filled with great fear that all the fruit trees in southern England would succumb to the embraces of my oleander scale insects.

As proper insecticides are no longer available to amateur gardeners, I was left with no alternative: the oleander and its guests had to go. And go they went — straight onto the drawing-room fire.

‘The Germans have already declared European hornets a protected species. I suppose it won’t be long before some idiot suggests we offer the same protection to Asiatic hornets’

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The usual English reaction when told of a new pest that threatens our way of life is to do too little, too late. I remember the first time I saw oak processionary caterpillars, in Italy at Villa Taranto on Lake Maggiore. The way they stomped along nose-to-tail seemed to me more comical than worrying. I pushed one aside and created chaos among its followers (I didn’t know then that the hairs along their backs carry an allergic irritant that can provoke a serious reaction).

The moths arrived in England (no one knows how) about 15 years ago. Yes, they were illegal immigrants, but no, no one did anything about them, at least not until it was too late. Money and manpower were short, so members of the public were just told to look out for them.

Of course, by the time people saw the caterpillars processing along and stripping our English oak trees of their leaves, it was too late. We shall never be rid of them now.

Warning signs that are too little, too late? The oak processionary moth.

Warning signs that are too little, too late? The oak processionary moth. Pic: Alamy

We haven’t been clever about Asiatic hornets either. They started off in Bordeaux in 2004 with just one queen hibernating in a consignment of garden pots from China. Honeybees are their diet of choice. No bees means fewer pollinators and more problems for our fruit trees. The French told us that the insects were progressing at a rate of about 100km every year, but we made no preparations for their arrival.

I have a house in the Cherbourg peninsula and first saw the Asiatic hornets two years ago. On warm evenings in May, I sit (wine glass in hand) by my collection of cotoneasters and slay the queens with common fly spray when they come to gorge themselves on the foul-smelling flowers.

The problem is that their nests (which are huge, as much as 6ft high) are always way up at the top of tall trees, hidden from view until the leaves fall away in autumn — by which time, it’s too late because next year’s queens have already escaped, mated, emigrated and bedded down for the winter.

However, 100km is 62 miles and much of the coast of northern France is closer to England than that. Asiatic hornets crossed the Channel in 2016 and no one has worked out how to stop them spreading.

An Asiatic hornet

An Asiatic hornet. Picture: Alamy

In France, the council will destroy their nests for free, but I can’t see the penny-pinching English following suit once they get established in places such as the New Forest, where no one will notice them anyway. Numbers were up in 2018: Asiatic hornets are here to stay.

I suppose we shall learn to live with them. After all, gardeners have to put up with rabbits, which were introduced as food by the Romans 1,900 years ago, although most of us would be glad to be rid of them. Our garden trees would be grateful if we could exterminate American grey squirrels and those ugly Asian brutes the muntjac deer — both do nothing but damage.

Badgers, alas, are native; I wish they would eat every Spanish bluebell that infests my garden, but they seem to prefer the dainty wild daffodils. They have their supporters and champions — all these furry creatures do. So cuddly.

The Germans (remember how powerful the Greens are there) have already declared European hornets a protected species. I suppose it won’t be long before some idiot suggests we offer the same protection to those fascinating and beautiful exotics the oak processionary moths and Asiatic hornets.

Charles Quest-Ritson is the author of the RHS Encyclopedia of Roses