getting montbreshia out of lawn

Montbretia (Crocosmia masonorum) is a corm (a sort of bulb) - it sounds as if the landscapers were a little careless in removing and disposing of the corms when they dug it out and the corms have been distributed in the topsoil in your lawn. I'd contact the company and get them to sort it out - they should have been more careful. The only option is for someone to dig out each corm as soon as possible and repair the lawn afterwards. I should point out that this plant multiplies very quickly - within a season, where there's one corm, there'll soon be several.

or you could carefully 'paint' weedkiller on to these leaves. carefully avoiding splashing the grass. a long job. but if you paid to have the montbretia removed i'd ring the company and get them to sort it as bamboo suggests.