Tomatoes and lavender at risk of decimation by foreign pests, RHS warns gardeners

Tomato and lavender plants are under threat of decimation by foreign pests and diseases, the Royal Horticultural Society (RHS) has said as it appoints a new head of plant health.

Warmer weather is causing pests and diseases from warmer climates to do better in the UK by speeding up their life cycle, the charity has warned.

While many of these diseases used to mainly survive solely in glasshouses, they are now becoming more common in gardens. The foreign diseases are usually imported by accident in crops and garden plants from abroad.

One such pest is the brown marmorated stink bug, originally from Asia. Experts warn the bug is likely to spread across the UK in coming years as it favours warm weather. It is capable of ruining crops such as apples and tomatoes and hibernates in homes during the winter months; clustering around window sills and releasing a foul smell.

Another under investigation is Xylella fastidiosa, a plant bacterium not yet in the UK but present on the continent, which is known to kill as many as 500 host plants including garden favourites such as lavender and rosemary

The new Head of Plant Health, Glen Powell, used to work at the National Institute of Agricultural Botany. He told The Telegraph: “Of particular concern, not just for the RHS but £24billion horticulture industry as a whole, are new threats whose impact is as yet untested.

"This includes the brown marmorated stink bug which although present in the UK is not yet thought to have colonized and spread, the emerald ash borer beetle, rose rosette virus which has devastated entire collections in the US, rendering big, blousy blooms mere patches of soil, and Xylella which has brought destruction and decay to olive groves and lavender fields on the continent. If Xylella were found in the UK all host plants within 100m would be destroyed and there would be restrictions on movement of plants within a 5km radius for five years – sounding a death knell for gardens, nurseries and garden centres.”

The plant charity has set up a new lab at RHS Garden Wisely to facilitate the expansion of its work into detecting, identifying and managing plant health problems and help eradicate pests from the garden. The new purpose-built laboratories include facilities for molecular diagnosis of plant pests and pathogens and investigating safely-contained biosecurity organisms under licence.

Plant health is becoming a growing issue for gardeners, and the RHS team responded to 22,385 gardener enquiries, up 87 per cent on the previous year.

Mr Powell said this is also true of RHS gardens, with pests munching star blooms. He explained: “The RHS, like gardeners across the country, fights a daily battle with pests and disease on our plots but we’ve learnt to take a more balanced view, often overlooking those that cause only surface level damage. That’s why you might see the tell-tale sign of slugs on our vegetable beds and rust on leaves in our orchards."