I should preface this by acknowledging that this is a first world problem.

Regardless, as this is my first garden, or rather the first I am responsible for, it is with much regret that after many weeks of cultivation I finally got my grass the way I wanted it, no moss, lush and full it looked a million dollars until I sprayed weedkiller too close to the aforementioned lush greenness and a big strip of it started to go yellow/brown.

The wind having carried the agent orange onto my pride and joy, should I just re-seed the bit I’ve killed?

No. Just accept.

In November, cut out the duff bit and stick down some turf. Life’s too short etc:-)

Dammit, I thought you might say that.

orrrr. if you want to, heavy rake, and reseed after about 4 weeks from the time of killing.

Reseed past the edge, so you get a blend, the risk of laying turf is a visible boundary, but it is more reliable. You could returf, then heavy rake and reseed to blend in spring. Best of both worlds.

if you insist of a “pure lawn” consider an area of wild meadow seed for bio diversity somewhere in your garden, will encourage wildlife and increase your enjoyment of your garden.

If you re-seed you may have a different grass type to the rest of the lawn. This may look odd. One possible solution is to cut out small pieces of untouched turf and replant in the bad area. Not aiming for the whole lot but spaced, they can then grow outwards. It will look a bit funny until it all joins up. The Agent Orange should have dissipated in the soil once it’s done its job.