Upsy Might be a good idea to take a pair of scissors to cut off all the flowers first and then spray on the small ones in gaps and the biggest clumps. I used to have exactly the same. Fortunately, they bordered on the lawn, not concrete ground, so I just removed them. I have planted something new straight away and the new plants took, so it's more or less OK! Mine was never as spectacular as yours though!
Trouble is when the seedheads land in the gap of hot bricks, they just grow. A knife and a Resolva are my weapons.
See, now I have only got one.
I used to have masses of them.
Now I have headache from chamomiles. See the little flowers. Some have flown away as tiny seeds and landed in between the gaps of the slab paving in the front.
See the osmanthus being covered by the Leucanthemum? Two tiny osmanthus all covered by Leucanthemum.