[Anton]

Dear Allotment Growers,

One of my fellow allotment growers is worried about just one of his potato plants that has taken a turn for the worse. He feels his English might let him down so asked me to seek  your opinion on his behalf. I suggested it might be blight. So what do you think (looking at the attached picture) and if it is blight what do you think he should do? I had a solitary plant that was affected by blight two years ago (it even when black at the bottome of the stem which is not the case with my neighbour's plant - yet) and I just pulled out the whole plant and binned it and then sprayed the rest of the plants with that copper mixture thing (whose name escapes me). Fortunately, it didn't spread. I look forward to hearing your expert opinions.
(sorry for any inconvenience caused by my technical incompetence trying to upload the photo - it was too big so I had to keep reducing it)

Anton

[HilaryG]

Doesn't look like blight to me! Maybe something ate through the stem?

[DD.]

Hello Anton.

Firstly, that's not blight, it does not have the yellowing & blackening characteristics of blight.

Also I doubt you had blight on a previous occasion as almost certainly it would have spread to other plants by the time you used the spray, which I assume was Bordeaux mix. It sounds to me that the single tuber had "blackleg".

This plant looks as though it never been as strong as the others.

Sometimes a single plant can die for no apparant reason, whatever, I would still dig it up, but rest assured - that is not blight!

[Anton]

Thanks for all the replies, so far. By the way DD, the plant I took out and  destroyed stank to high heaven, which is I why I thought it might be blight (after seeing various descriptions of the illness on this site). Is blackleg associated with any rank odour? (That's the name, Bordeaux mix, the French version doesn't trip lightly off the (or rather my) tongue)
Anton

[peapod]

Seems like a bad one to me too, smell points to maybe scab? Good thing to take it out.  I had one dustbin on my plot full of Vivaldi that looked bad, so it was banished! Thankfully my mains seem ok and I caught it quickly

[DD.]

Is blackleg associated with any rank odour?

Any potato that's gone bad for whatever reason will stink to high heaven! It's a smell never forgotten!

[JWK]

The old seed tuber will rot away and can smell very bad sometimes, even though the plant is OK and the new spuds are just fine.