I'm also in the Hudson Valley, in the forested area. Stiltgrass is a monster invasive here, covering roadsides and forest floors, preventing any form of plant growth besides itself. Pull it out before it spreads its seed. Throw it in the trash. It's an annual that when mowed, will make its seed at a lower level.

In your garden, keep pulling it every year till it's gone.

I can't advise you on herbicides. Just want to sympathize with you.

I say over and over again when I see it, "I am powerless over you." Monster.

1. The problem is knowing when to pull it out because there seems to be no visible seed. I am curious, how does it prevent other plant growth? Is it alleopathic? It doesn't seem to be dense enough to shade or crowd out other plants. If it is alleopathic then it would be important to pull it regardless of the stage of seed formation. It's just awful. I would have to employ an army to ever get on top of it. I regret ever clearing an area before replanting - and densely enough to prevent it from getting a toehold. Too late now...

If you do a search for japanese stiltgrass and images, you will see how it grows and crowds every other plant out. You can also learn about its behavior. The images will show you where the flowers are. They look like thin grass flowers. Around here they are in flower all along the roads and woods and have gone to viable seed. The grass seems to turn tan color when seeds are ripe.

Pull the plants in spring when they are young. They are easy to pull. There is another thread in the weeds forum that discusses herbicide poisons to use.

Good luck! I've given up except for in or near my gardens. It's everywhere.

I have the same situation: Large areas planted with forbs (i.e. plants that aren't grasses), and invasion by grasses including stiltgrass. When I saw how destructive stiltgrass can be once it gets a foothold, I realized I had to expand my chemical repertoire beyond glyphosate. So now I use Grass Beater, a brand of selective herbicide that targets only grasses. It's more complicated to use than glyphosate because you have to mix it with oil, and it's more expensive. But it's been a huge help in deterring the invasion of my "meadows" by grasses, so I have more energy to spend on non-grass invaders.

Grass Beater is not for sale in New York, among other states.