Try an old trick.

Drop fertilizer now ASAP and irrigate to give the weeds a flush of growth. Yes, you want to grow weeds, LOL!
Weeds need to be actively growing for herbicides to work.
2 or 3 weeks later, now the weeds are growing and hungry, it's time to zap them.

2 or 3 apps of Triclopyr is needed for Charlie. See link below.

Another trick is to give Charlie a double barrel zap.
Using a tank sprayer, (2 to 3 weeks after fertilizing) mix the Triclopyr as directed along with this product, which contains Quinclorac as directed, together in the same mix.

http://www.scotts.com/smg/products/ortho/weed_killers/weeds_in_lawn/pdf/WBGCrabgrassConc_042009.pdf

Due note, the above is the newest product. Older versions do not contain Quinclorac.

Again, multiply apps are required for Charlie - you'll win the fight.

Here is a link that might be useful: Weed B Gone Chickweed and Oxalis killer