Brown spots on potato leaves

[mrsbusy]

Hi any potato experts please could you advise if the leaves in photo are normal or is this blight - the plants still have lots of green leaves but they all have a few with these brown spots. Thank you.

[Jungle Jane]

It does look like blight,those concentric rings inside the brown look like it,have you seen any markings on the stems? Is it on the one plant? I wonder if it was all the rain but humid weather…Clean the cutters you used in case it spreads the spores to other plants. I would remove the affected stems of that plant & watch carefully for signs on other plants.

[ameno]

It's early blight. It's a complete separate disease from late blight (the devastating one).
Early blight attacks most often during hot, dry weather, and causes those brown spots with concentric rings of dead tissue in them.
It can largely be safely ignored. It only attacks the leaves and not the tubers or stems, so cannot ruin the crop or kill the plant. If the infection gets really bad it can defoliate the plant, but that's very unlikely to happen in this country. Removing infected leaves will do more harm than good, so just ignore it and don't worry too much about it.

[mrsbusy]

The plants look healthy and there are no spores to see on the back of the affected leaves..I was a bit surprised as they are Sarpos
which are meant to have good resistance to blight. But I did use last year's tomato compost along with new compost and they did have blight. I know now that I should not have used it.

[ameno]

It's not the same blight. They might have the same name, but the two diseases are completely unrelated, with different symptoms.
If your tomatoes got late blight (the proper blight) last year then that cannot cause anything to be infected with early blight, which is what your potatoes have now (and that's setting aside the fact that late blight cannot survive without a living host for more than a few weeks, so will not survive the winter in the compost heap unless you also have potato tubers in there).

Sarpo potatoes, by the way, are bred for resistance to late blight, not early blight. I don't think their early blight resistance is meant to be anything remarkable. But as I said before, early blight is mostly harmless (it's rare to get a serious infection in this country, as it prefers hot, dry conditions. Plus it's only a leaf disease in the first place).