I tested 3 herbicides and kept an untreated control using marigold seedlings as a test"weed". (Easy to grow.)
After 48 hours the untreated control looked OK. Treatment with T-Zone cause rapid collapse. Treatment with Speedzone was effective. Treatment with Quicksilver was slightly less effective.
I hope to have a chance to try this with chickweed. (Dug up and moved inside). Perhaps I will try some mixtures of above products.