OK, let’s be honest – you probably wouldn’t be instinctively drawn to a headline about biosecurity. Indeed, I suspect many people don’t really understand what it is (in case you’re wondering, in its broadest sense, it’s “actions taken to prevent damage by biological threats”). Here, not surprisingly, I’m talking mainly about disease threats to plants in our gardens and countryside.
I’m sure most readers will be familiar with Dutch Elm Disease, transmitted by a beetle that was brought here in a load of timber, and which eliminated our native elms from the countryside. But how many of us have all but forgotten about “Chalara” ash die back (Hymenoscyphus fraxineus), which featured in the media a few years ago but has since faded from the limelight? (The fungus was previously called Chalara fraxinea, hence the name of the disease.)
The first case of Chalara ash die back in the UK was in February 2012, when it was found in a consignment of infected trees sent from the Netherlands to a nursery in Buckinghamshire. A small number of cases were identified in Norfolk and Suffolk in October 2012, and it has since been confirmed in most of the UK and Ireland, with the first confirmed case on the Isle of Man in 2017. Long term, it is anticipated that almost all our ash trees, which represent about 30% of our natural tree cover, will be affected. There is more detailed advice available for woodland owners, but in garden situations you can help to slow the spread of the disease by removing and disposing of infected ash plants, and collecting up and burning (where permitted), burying or composting the fallen leaves. This breaks the fungus’s life cycle. A Plant Health Order prohibits all imports of ash seeds, plants and trees, and all internal movement of ash seeds, plants and trees.
Right now the tree and horticultural industry is anxiously watching out for a “new” disease threat – Xylella fastidiosa – a disease that affects a wide range of plants such as grapevine, citrus and olive plants, lavender, oleander, hebe, rosemary, plane trees, our native oak and numerous other trees, shrubs and herbaceous garden plants. Although not present in the UK yet (aside from one case involving an infected ornamental coffee plant, which was destroyed), there is a very real risk of it being accidentally introduced since it was discovered in Italy in 2013 (where it has decimated olive groves), and Corsica and mainland France in 2015 and Spain in 2017 (killing many old olive trees and grape vines).
You don’t need a particularly vivid imagination to envisage the devastation Xylella would cause in our gardens and countryside. It is locally transmitted by leafhoppers and spittle bugs, but long distance transmission is by the movement of infected plants, and so we all have a duty to pay particular attention to where we source our plants: notwithstanding emergency measures imposed by the EU, it has never been more important to source plants and trees grown locally within the UK wherever possible.
There are plenty of other problematic plant diseases that have arrived in the UK in recent years, invariably as a result of importing infected plants – both commercially and personal imports by individuals, including:
- box moth caterpillar
- box blight
- fuchsia gall mites
- oak processionary moth
- Phytophthora diseases
- sweet chestnut blight
… and several others, quite aside from the many diseases not yet present but that still pose a very real threat.
So what can we each, as individuals, do? Well, first and foremost, don’t bring home plants from abroad! Secondly, try to obtain home-grown plants whenever possible. Sadly this isn’t always feasibly, and in any case it may be impossible to tell – plants, trees in particular, have often been grown in several European countries before being imported for sale in the UK. Inspect all plants carefully an arrival, and reject any that appear diseased. Nurseries and commercial suppliers have a duty to trade only in certified stock, although the present EU plant passport system is pretty useless for establishing traceability, whilst the ministry have implemented special checks for Xylella-susceptible imports, for example.
It’s also worth considering some practical precautions in your own garden: bacterial and fungal diseases are easily transmitted on garden tools and they should be disinfected before being used elsewhere. If you employ a gardener, it may be simpler to insist they use tools that you provide, and leave their own tools at home.