I have a couple of areas of lawn that I have been trying to maintain to
a high standard over the last 5 years, to get that green carpet effect.
I feed, weed, mosskill, water and mow with a cylinder mower regularly.

It has been going quite well but suddenly this year I have large patches
of whitish seed heads appearing in a number of areas. It is obviously
some sort of grass, so I don't suppose it will be affected by lawn
weedkillers. I've lowered the cutters on my mower which removed some,
but nothing like all of the seedheads.

Any ideas about how I can discourage this stuff?

TIA

Steve