I don't know what the plant is. Preen stops seeds from sprouting but doesn't impact plants that were already in place. Have you pulled any of these to see if they are actually new sprouts, or if they are growing from roots left in the ground?

It is Mugwort, Artemisia vulgaris. It is spreading by runners so Preen will not help. Sadly most apps are not very accurate. This is a case in point. Hedge Mustard doesn't look much like this at all.

There are some fun apps that IDs plants. Some are free or have a free trial. If you have an Android phone, PlantNet continues to be free to me and Picture This was fun while it lasted.

^^^ Plant ID apps are notoriously inaccurate. They have about a 50% success rate.

OTOH, the Name That Plant forum here is incredibly accurate, specially when folks like floral, Jay or macranthos get involved. Just may take a little bit longer.

Thanks. I tried an app and it said hedgemustard. I don’t think that’s it.

I pulled some and they have underground stringers (maybe a bad term - but like a raspberry bush). They seem to be the only thing coming up since the preen was put down. I’ll keep pulling - but if there was another way to treat - I’m all ears.

It is definitely not Hedge Mustard. They are what I said they were above, Artemisia vulgaris. I would just dig it out.