If I understand correctly, you have decided to let it germinate, going forward. You want to kill it at some point after it emerges, without the dead crabgrass being evident to the casual observer. Your brother in law can accept this, but not you.

Thus, the best time for you to kill it will be very shortly after it emerges next year. There will be lots of it to eliminate.

Hi rifis,

I have not decided yet what would be the proper approach.

I am seeking suggestion/advice if it would be better to kill it now or if it would be okay to wait.

Thanks

Kill it now. While unattractive in the extreme, you'll limit the seed it drops. Then, remove the worst visual offenders that really stick up while you casually remove the rest if you have the time and if you feel like it--no pressure and no rush.

And no worries that they're seeding out all over your lawn for next year, waiting to cause the same problem. Or worse.

Next year, use a pre-emergent. It should help to limit the sprout of crabgrass, at least to some extent.

If you can--it's getting tight--and if you have the inclination, reseed or move bits of existing misplaced sod from gardens and landscaping into areas where the CG is growing. Water for several weeks to establish. Feed well to encourage spread and, over time, they'll make a dense lawn that won't allow CG. You know the drill. I just don't get the stuff except in the gardens and pots.

"Look good. Make people jealous." -- Kevin, Diamond City barber, Fallout 4

Thanks morph,

I appreciate your help as always...