potato problems

[dancing homer]

Well this is my first proper thread, so be gentle with me.
My potatoes are exhibiting the following symptoms.
new leaves showed small brown pinhead marks and now show brown blotches, which seem to appear on the newest leaves first.
The blotches are brown with a darker ring around the outside. There is almost no yellowing of the leaves, and the brown marks run along the lines of the leaf veins.
I have sprayed the plants twice in the last 12 days using one of the Bordeaux mixtures, and aside from giving the plants a rather fetching blue green sheen, it does not seem to have any effect.
Now experience when I was a youngster in my Dad's garden, makes me think that this is a pretty clear cut of what he used to call early blight. But I have never really been sure of the difference between early and late.
Any help or background would be appreciated.

[Demeter]

Hi there - a few threads recently have discussed signs of blight (use your search button, look for "blight" and several will come up). The consensus seems to be that blight is black and slimy and stinky, which doesn't sound like what you've got. (Not going by personal experience, mind, as this is my first year - so do check out those other threads!)

[dandamegs]

Magnesium deficiency?

Are the leaves brittle?

[terrier]

I think for Bordeaux mixture to work you have to spray and keep spraying BEFORE you get blight. Blight evidently requires a certain set of temp/humidity/time to get going; without knowing your exact weather conditions at the moment, it's impossible to tell as there are many reasons for marks on leaves. All my potato plants had spots on the leaves last season and I still got a good crop, so for the moment all you can do is keep your fingers crossed. As dandamegs says it could be poor growing conditions causing a vitimin deficiency.

[dancing homer]

The leaves aren't brittle at all. In fact other than the marks themsleves, it sems to have no ill effect. The stems look pretty healthy.
Since the first post, a few more of the plants have developed the same symptoms.
I have pulled the ones that seem to be the worst, and the tubers are very healthy and taste delicious.
In terms of the weather, we had almost a week of ideal temperatures two weeks past, and it was after this that the symptoms started.
It may indeed be a vitamin deficiency, and I will get to work on the soil for next years planting season. I will be rotating potatoes out of the beds anyway, so that will allow me a chance to get things sorted for three years when they will be put back.
Thanks again for the info, it really does help innocent novices like me.