Haystack, I'm not sure if I posted anything earlier about it, but everything you said is helpful. Based on the pic you provided, I am seeing some horseweed, however the weed that is giving me the biggest problem is more broadleafed - I used to describe it as looking like giant carrot tops. I guess the butyrac would work on it - and it's certainly a LOT less expensive.
Regarding mowing . . . how tall should I let it get . . . or just wait for it to flower first?