White pimples on turnip leaves

Weeding, if you turn the leaves over you will probably spot little bugs where the white pimples are

no, that's just it. We've looked long and hard, and can see nothing, nor inside the pimples.
Has anyone else who's growing turnips now had the same nobbles please?

In a book I have it describes White Blister Disease. It's a fungus and you have to destroy the plants. You could Google it to find out more maybe.

Yes a fungus which can affect all brassicas, usually after wet/humid conditions destroy them and don't grow brassicas in that area for 3 years, the spores stay in the soil. Do you practice rotation?
Also to increase your plants resistance to disease generally,
try natural no dig gardening, top dress wifh compost / mulch, try not to leave bare soil. If you think about it in forests and woodland nothing is fertilised or tilled and yet it all flourishes.
Undisturbed the soil bacteria and mycelium thrive and attach to plant roots improving resistence to disease.
Here is a link
http://davesgarden.com/guides/articles/view/208/?utm_source=nl_2008-02-25&utm_medium=email
and another -
http://www.no-dig-vegetablegarden.com/index.html

Thanks all for finding out - from the images I've found online tho, so far what we have is not similar to either white blister or another one (something? chrysanthemum fungus).
I might just be deluding myself, but I'm convinced that these plants are definitely thriving. Husband is not really in agreement! The thing is, these dots or pimples are quite regularly spaced, so that does not fit with the two villains mentioned above.
Hm.
To cap it all, I've realised that a tip-off from a kind friend who helped us fell trees and replace boundary fence has materialised as true - definitely Jap. knotweed in the council's field just beyond.
Aargh!