Sandy's Garden ... I Don't Believe It

For the first time since 2017, slugs and snails topped the UK gardeners’ list of garden pests in 2020.

Tuesday, 16th March 2021, 9:38 am

That’s according to the recently-revealed results of the Royal Horticultural Society’s (RHS) annual survey.

My personal research into this matter in my own garden agree very broadly with this UK-wide finding, though I would be tempted to place snails on their own on the gold medal podium, with slugs taking the silver medal.

What I find more difficult to accept is that for the three previous years snails and slugs were ousted from top spot by other pests, including box tree caterpillars and vine weevils.

Falkirk Herald gardening guru Sandy Simpson

I don’t believe it!

Not in my back garden they weren’t!

Slugs and snails have continued to dominate my personal list of pests, as they have dominated national lists for many of the past 25 years.

And box tree caterpillars? Have I ever as much as seen a box tree caterpillar, let alone found it to be the worst pest in my garden?

The first box tree caterpillars to be found in the United Kingdom were discovered in the home counties as recently as 2011, although adult moths were first recorded here in 2007.

However, the moths’ ability to breed and thrive here resulted in the bug spreading across the south-east of England so rapidly that this native of East Asia was deemed to be the UK’s top garden pest in the RHS survey in 2015.

To illustrate the rapidity with which the numbers of box tree moths mushroomed, the RHS received over 800 records of the moth between 2015 and 2016, 3 000 in 2017, over 6 000 in 2018 and approaching 12 000 in 2019.

Mark you, its arrival – and probable increase in Scotland – isn’t necessarily a reason for local gardeners to follow Private Frazer’s example in Dad’s Army by declaring, “We’re doomed; doomed, I tell you.”

The website of the European Boxwood and Topiary Society (EBTS) gives a summary of the box tree moth’s lifestyle.

“The moth lays pale yellow eggs on the underside a box leaves. When the eggs hatch the greenish yellow caterpillars eat the leaves and produce a cobwebbing and a trail of pellets in their wake.

These caterpillars can survive over winter down to -30°C and becomes pupae in a chrysalis before emerging as white, semi-transparent moths.”

So box tree moths live up to their name and need to find box trees to thrive. They won’t like my garden, which is box tree free. And, since the EBTS also advises that they prefer temperatures of between 21°C and 33°C and only feed at 15°C or more, they may not be too happy in central Scotland despite having no natural predators here.

Box trees are used by topiarists and as hedging plants and are possibly more common in Scottish parks than in gardens. The caterpillars are bad news for the trees, whose leaves they devour, sometimes actually killing the plants: but there aren’t too many box trees around Falkirk, so we may find it hard to believe that box tree caterpillars are our worst garden pest.