Spots on potato leaves

[Mushroom]

I have 2 potato plants in large pots that were grown from proper seed potatoes from a garden centre, in brand new compost.
They grew well, but have now got lots of little brown spots over most of the leaves, though they're still green otherwise.
Pics of potato blight i have seen online have got big brown spots and yellow leaves. Would it be potato blight i have, and if so, shall I just throw the plants away now?
I started some more off in the veg patch a week ago- might they get it too as they are near the affected ones?

[nick the grief]

I wouldn't have thought it was blight yet. A couple of mine have the same but tis was caused by a hail storm we had recently I think as they were clear till then. If it is blight your others will probably be OK just make sure you put the Haulms (tops) in the recycle bin or Dustbin and don't compost it, you won't be able to generate enough heat to kill any spores and do the same with the compost or you could steralise it your self with a couple of Biscuit tins and your oven

[Cutecumber]

I think I know what this is - I've just noticed it on mine this morning. It's the same as you sometimes get on tomato leaves.

I believe it is a nutrient deficiency - I think it's due to a shortage of magnesium. I'll try and find a picture and you can see if it's the same.

[Cutecumber]

check the picture on this page, half way down

http://www.rhs.org.uk/advice/profile...toproblems.asp

[jondanie]

Mushroom,
I would agree with Nick as to what it is, but without a pic of the affected leaves/plant, it's difficult to give a definitive answer. Is the whole plant affected or just some of the leaves? Did the symptoms appear all of a sudden or has it been getting worse over a number of days or weeks?

The brown spot symptoms you described would not be typical of magnesium deficiency, though the pic from Cutecumber's RHS weblink above would suggest so. However,in the pic the inter-veinal yellowing is the actual deficiency symptom, not the apparent brown marks)

If you can upload a pic, it would be a big help,

Hope this helps

[Cutecumber]

To me, the description doesn't sound like blight - you get large spots and patches, not little brown bits.

You do get brown marks from magnesium probs too - honest! I've got it and it is not blight. My potatoes are coming up to harvest so I would expect that nutrients are running low.

I'll have to find some more pictures...

[Cutecumber]

I found something useful, possibly - doesn't support my case in any way, though!!

It looks like mine have canker! lol!

tomato leaf pictures

Obviously, these are tomato leaves, not potato, but it's a start.

[Alice]

check the picture on this page, half way down

http://www.rhs.org.uk/advice/profile...toproblems.asp

Thanks Cutecumber, I've looked at that, but the description of magnesium deficiency doesn't seem to fit the picture of the leaves with the brown spots which goes with it.

[jondanie]

Alice,
I've taken another look at that RHS pic and from what I learned in my college days, it looks more like potassium deficiency.

The brown spotting is pretty characteristic of potassium deficiency.

I would suggest applying some high K fertiliser, like tomato food which should help.