Flavescence dorée or bois noir? How to tell them apart

Two phytoplasmas, one set of symptoms

Both are called "grapevine yellows" and both are caused by phytoplasmas, wall-less bacteria living in the plant's phloem. Flavescence dorée is associated with phytoplasmas of ribosomal group 16SrV ("Candidatus Phytoplasma vitis"); bois noir with "Candidatus Phytoplasma solani", group 16SrXII.

They are different organisms. But the vine reacts to both the same way, and that is the heart of the problem: on leaves, canes and bunches, bois noir symptoms are not distinguishable from flavescence dorée. Not "similar": not distinguishable. No shade of colour, no detail of the leaf roll lets you honestly say which one you're looking at.

The real difference is who carries them

If the plants don't help, the insects do. This is where the two diseases diverge completely:

• Flavescence dorée — the vector is Scaphoideus titanus, a leafhopper that completes its entire life cycle on grapevine. It lives there, gets infected there, and transmits vine to vine.
• Bois noir — the vector is Hyalesthes obsoletus, a cixiid that lives mainly on herbaceous plants such as nettle and bindweed. It picks up the phytoplasma there, and only occasionally visits the vineyard.

Everything else follows from that. Flavescence dorée has a vector that lives on the vine: it can spread plant to plant, epidemically. Bois noir cannot: its vector comes from outside, bites, and leaves. The vine is a dead end, not a link in the chain.

That's why the same yellow patch on two identical leaves means opposite things: in one case an outbreak running through the vineyard, in the other an accident arriving from the weeds at the field margin.

And here the law comes in

The practical consequence isn't academic. Flavescence dorée is an EU quarantine organism — listed in Implementing Regulation (EU) 2019/2072 under code PHYP64 — and Implementing Regulation (EU) 2022/1630 sets the measures for its containment inside demarcated areas.

Bois noir is not a quarantine pest. No demarcated zones, no mandatory uprooting, no prescriptions: it is one grower's agronomic problem, to be managed through the cover crop and the host weeds.

Bluntly: faced with two vines showing the exact same symptom, in one case you have duties towards the plant protection authority and in the other you don't. And you cannot know which by looking.

Careful: the rule you'll find online is out of date

Search for Italy's mandatory control rules on flavescence dorée and you will almost certainly land on the Ministerial Decree of 31 May 2000. Half the web still cites it, including recently updated pages.

It is repealed. Ministerial Decree 292676 of 6 June 2023 (Official Gazette of 11 August 2023, no. 187) abrogated it, and the matter passed to Ministerial Ordinance no. 4 of 22 June 2023, which redefines the emergency phytosanitary measures against Grapevine flavescence dorée phytoplasma.

There is a second layer, though, and it's the one that actually matters to anyone with a vineyard: the operative prescriptions are regional, and reissued every year. Piedmont, for instance, works under directorial decree no. 280 of 16 March 2026; the year before it was no. 268. Zone boundaries change, so do the windows for mandatory treatments against Scaphoideus titanus, and the reporting procedures.

That's why you won't find a checklist of duties here: it would be wrong by construction, because it depends on your region and the year. The only valid reference is this year's decree in your region, and your regional plant protection service is the right party to ask. Be wary of anyone — us included — handing you a one-size-fits-all list.

What confusing them costs

The mistake costs in both directions, but not equally.

• Taking bois noir for flavescence dorée — you uproot vines you could have kept and spray insecticide against a vector, Scaphoideus titanus, that has nothing to do with the disease you actually have. You spend, you damage the vineyard, and you don't fix it: the real vector is in the weeds, and insecticide on the vine never reaches it.
• Taking flavescence dorée for bois noir — this is the serious one. You don't report, don't uproot, don't treat the vector. But that vector lives on the vine, and the outbreak spreads plant to plant while you treat it as your own private business. Beyond the damage, you are outside the duties that apply to a quarantine organism.

The asymmetry is stark: erring one way costs money; erring the other lets an epidemic run and puts you out of compliance.

Only the lab decides

There is no visual shortcut. To know which of the two phytoplasmas you have you need molecular analysis: PCR separates flavescence dorée's 16SrV group from bois noir's 16SrXII. It is the only instrument that answers the question.

Which brings us back to where all our work starts: in plant pathology, what matters is rarely visible. The symptom tells you something is wrong — not what, and sometimes not even whether it's your problem or the whole district's.

Where we fit

Our dog doesn't diagnose: the lab does, and no nose replaces a PCR. What we do is help narrow the field first: find the spots to check and sample, so the analyses go where they're needed rather than at random, and the technicians work from a map instead of a whole vineyard.

On how scent detection works and what it can and can't do, see our pages on flavescence dorée and on the method.