Most rampant

The first in the weeds/wildflowers series which will demonstrate my considerable ignorance of things botanical.

This one has taken over the northwest corner of the south-facing sandy patch.  I'm guessing it will be the most sheltered spot - i.e. furthest from wave action and south/south-westerly winds.  Possibly too there were more or different nutrients in this corner.  I find nothing particularly attractive about it, save a slight admiration for its sheer numbers.  I fear it will take over the entire area if left to its own devices.  Already its flowers are falling in this afternoon's heavy rain.  Thoughts/advice/name(?) welcome.

If I'm right about the shelter/nutrient theory it might be a spot for a climbing hydrangea which might survive the storms and is salt tolerant but I'd have to deter these fellas and improve the soil to give one a chance.  If I let these guys do their own thing till next spring am I sowing the seeds of doom?