Sedges have a triangular stem, so they're usually pretty easy to identify. Roll the stem. If it's a triangle, it's a sedge. This is one weed I actually do, occasionally get one or two of. Take care of them quickly or they do tend to spread.

They're also unbelievably resistant to most standard herbicides. You're not stating where you are or your lawn type, so our ability to suggest options are limited, but two to look into are Sedgehammer and Tenacity.

There are two common types of sedge problems in lawns. Most common is nutgrass or nutsedge. It is a water loving plant that's been seen growing on flood prone islands in rivers. Once the soil dries out, though, it can go away until the soil conditions become favorable again. People who water daily will complain about it while people who water weekly rarely have a problem.

The second common sedge is green kyllinga. GK and nutgrass look alike until they flower. GK has the ability to absolutely thrive during a drought. When the soil is dry and cracked open, the only plant left standing is green kyllinga.

Here is a picture of the green kyllinga flower.

Next are pictures of the two types of nutgrass/nutsedge.

Green kyllinga and nutgrass/nutsedge compared

For nutsedge, I just keep pulling them out. They might grow back but slowly but surely they die out. Easy to yank too.

And I can tell ya that nutsedge will absolutely survive a dry environment without issue. A lawn without rain for a month? No problem.