"Jack" wrote:
Hi,
I used
the same pesticide in other places and it did not happen; I also double
checked if I used the proper pesticide (i.e., selective, that kills only
weeds, NOT the grass). I am totally puzzled why it happened.

You may have burned the bentgrass in your lawn. It is more susceptible to
herbicide injury than blue or rye or fescue. Just a guess without seeing
it.

It may recover..or not. I've seen it survive roundup applications.