Have I waited too late to apply pre-emergent for Stickers?

Look down at the Atrazine post.

I’d apply it as soon as you can - I’m of the understanding lawn burweed seeds germinate when soil temperatures drop to 55-60 F for several consecutive days. But Simazine has post-emergent activity on young burweed so that should help you. Also be looking for young burweed in the lawn in Dec/January (look like little parsley plants) and if you see them, spray them then - you should get good control before the stickers (seeds) form.