EFSA on Xylella: No Cure, So Stop It Moving
Europe’s food safety agency says there is no record of Xylella fastidiosa ever being eradicated once it is established outdoors, so the priority must be stopping infected plants and insects from carrying it out of Puglia. EFSA published its urgent advice on Tuesday, a month after the bacterium was confirmed in dying olive trees near Lecce. Here is what the scientists said, what they still do not know, and what it means for growers and for anyone who buys olive trees.
What EFSA was asked, and what it said
After Italy reported the outbreak and asked for European help, the European Commission requested fast scientific advice from the European Food Safety Authority: which plants can host the bacterium, how it could enter and spread in the EU, and what could be done about it. EFSA’s statement was adopted on November 22 and published on November 26. It describes the Puglia outbreak as the first of its kind in the European Union, with olive trees affected over an area estimated at 8,000 hectares, some of them more than 100 years old.
| Question | EFSA’s answer |
|---|---|
| Which plants can carry it? | A very broad range, including almond, peach, plum, apricot, grapevine, citrus, coffee and olive, and also oak, elm, ginkgo and sunflower. Plants can carry it without symptoms. |
| How does it spread naturally? | Only through sap-sucking hopper insects, which generally fly no more than about 100 meters. |
| How does it travel far? | Mainly in plants for planting, and in infective insects riding along in plant consignments. |
| Fruit, wood, seeds, cut flowers? | Negligible or low risk as pathways. |
| Can it be wiped out? | No record of successful eradication once established outdoors. |
What should be done
Because it cannot be eradicated, EFSA says containment has to focus on those two long-distance routes, plants for planting and infective insects in consignments, using an integrated set of measures rather than any single fix. The options it lists include pest-free areas, surveillance, certification and testing of propagation material, production under screenhouses, control of the insect carriers, and treatment and inspection of consignments.
The trade in ornamental plants is the worry. It is huge and fast, which lets pests and their insect carriers survive the journey. EFSA notes that the bacterium has already been intercepted twice in France, in coffee plants from Central and South America, which is why it rates the plant trade as a likely route.
What is still unknown
A great deal. EFSA says that the trees in Puglia were generally affected by a complex of pests, Xylella together with several fungi and the leopard moth, and that the bacterium’s exact role in the olive decline is still under investigation. Nobody has yet identified which insect is carrying it there, or exactly which strain is involved. Until that is known, EFSA says, every sap-sucking insect in Europe that feeds on xylem should be treated as a potential carrier, and insecticide spraying is unlikely to control the spread until the epidemiology is much clearer.
The agency’s plant health panel will now carry out a full risk assessment for the whole EU. That will take longer. In the meantime, the job falls to the Commission and the member states.
- For Puglia’s growers: the priority is keeping plants and insects from leaving the affected area.
- For nurseries: certification and testing of olive and other host plants is likely to tighten.
- For everyone else: this is now a European problem, not an Italian one.
Old olive trees are big business. Mature and even centuries-old trees are dug up in the south and trucked north to garden centers, hotels and roundabouts, because buyers love an instant ancient tree. That is exactly the “plants for planting” pathway EFSA is warning about, and it is the least necessary olive trade there is. If you are buying an olive tree, ask where it was grown. A young tree raised by a reputable nursery near you is the safer choice, and it will settle in faster too.
Sources
- EFSA: EFSA issues urgent advice on plant bacteria Xylella fastidiosa (November 26, 2013, archived)
- EFSA Journal 2013;11(11):3468: Statement of EFSA on host plants, entry and spread pathways and risk reduction options for Xylella fastidiosa (archived)
- Olive Oil Times: Italy Seeks Help to Contain Olive Tree Killer (November 6, 2013)