Potato Patch Problems

Last evening I was doing a spot of weed-pulling when I noticed one of the potato plants' leaves looking yellow and rather sorry for itself.  I think possibly potato blight has set in - I removed the leaves, in the hope that it won't reach the potatoes.  It is strange that none of the potatoes have any flowers on them yet - a sign they are ready for digging up.  So, in light of the yellowing leaves, perhaps something more sinister is going on.  I will dig up the affected plant this evening and keep my fingers crossed that I'm not going to lose all the crop.

The above picture is Anthemis (I think the name may be changed and it is now called Argyranthemum, but I can't be sure).  Anyway, this plant is standing proud at three feet tall, but has had to be staked, as it has a tendency to fall forward.  When it touches the ground it then heads skyward so you get bent stems, which look awful if you try to stand them up again.  The one pictured has been staked, the picture below hasn't - 

p.s.  I have just been informed that they are still called Anthemis (Argyranthemums are the small white daisy type).