Japanese Stiltgrass is an invasive annual weed that comes up each spring from seeds in the soil.

Preventing it from going to seed is a good start. It is easy to pull up before they "bloom" and ripen seed. If they have already produced the feathery seed head in your area, bag them up and throw them away. You can also cut it back with a mower or string trimmer and bag the grass and dispose of. 

 Remove the ones near where you need to over-seed your lawn this fall. Seeding in the fall is preferable to spring because there is less weed competition for crabgrass and stiltgrass. 

You can also apply a pre-emergent herbicide, before the stiltgrass emerges in the spring in order to suppress germination. Apply a preemergent without nitrogen fertilizer. Look for the active ingredient: Prodiamine (Barricade) or other preemergents labeled for crabgrass control. Apply in early spring (March) before it germinates. It germinates earlier than crabgrass so to prevent Japanese stiltgrass the preemergent needs to be applied a couple of weeks earlier than for crabgrass prevention. Here is more on mechanical and chemical treatment in lawns https://extension.umd.edu/resource/japanese-stiltgrass

Marian