What, in all creation, could possibly bring these three words together in one UK-newsworthy sentence? And that’s how I learned about a deadly plant disease called Xylella, an infection which has been memorably described as causing affected plants to die from the inside out. Once these nasty bacteria get inside a plant they spread slowly colonising the xylem - the small, straw-like tubes which transport water from the plant’s roots to its stems, shoots and leaves. Inside this xylem, the bacteria combine with other microorganisms to form a biofilm … a sort of slime … which thickens and sticks to the inside surfaces of the tubes. And, just like what happens below your kitchen sink when the outlet pipe becomes blocked, the water can’t go where it’s meant to go. At home, your washing-up water stays in the sink. In plants, of course, the water can’t get through the xylem with usually fatal results; and, at present, there’s no known remedy.
Xylella, I learn, was known in the Americas and Taiwan but had never been seen in Europe before it was identified in olive trees in the Puglia region of Italy in 2013; and its discovery there set off alarm bells across the scientific and political communities of the European Union. Olive oil is a major contributor to the economies of Italy and Spain, which together account for 70% of the entire world’s olive production. Any deadly threat to their olive plantations threatens the entire European economy. In 2014, the European Union ordered Italy to eradicate all the plants known to be infected or suspected of being so. This meant farmers were told to uproot and burn their precious trees, many of them centuries old … and they were not happy! The infection has been dubbed Olive Quick Decline Syndrome (OQDS) in Europe and has spread in just six-or-so years to France, Spain and Germany. It is now recognised that it is being spread around Europe by insects called leafhoppers and froghoppers which feed on xylem fluid and are commonly called ‘spittlebugs’, since their feeding habits leave blobs of frothy spittle, sometimes called cuckoo spit, on the plants. In the past, spittlebug activity didn’t harm plants: but a spittlebug carrying the Xylella bacterium spreads the infection with gay abandon as it does what spittlebugs do naturally.
There seems to be no general agreement as to the means by which the disease reached Italy. But it’s spreading rapidly through our continental neighbours and, although leafhoppers fly only short distances, as their name implies, they can be carried much greater distances by the wind or by hitching a ride on plants being moved from one country to another. ‘So how does that concern me?’ I asked myself. The last time I looked I didn’t see any olive trees in my garden or in any of my neighbours’ gardens. Why should I help scientists to record sightings of cuckoo spit and spittlebugs across the UK, as Dr Rebekah Robinson, senior plant pathologist at the Royal Horticultural Society (RHS), has asked volunteers to do, compiling a database to map the distribution of the insect in what is hoped will be a pre-emptive strike against a deadly disease when it crosses the English Channel.
And Dr Robinson provides the answer to my question. “One of the really devastating things that could happen is that it could affect our native tree species, things like oak trees, a number of different ash species, sycamore - key plants in our landscape.” For, despite having been dubbed OQDS, the disease can also infect more than 350 different plant species. So, although Xylella will probably arrive in England before it reaches Scotland, if you want to help with the spittlebug survey, go to https://www.brc.ac.uk/irecord/xylem-feeding-insects.