The little 'weed patrol' is quite a hoot, let me tell ya!!! The damn goats can get thru the eye of a needle!!! But they love weeds---and they love willows and scrubbrush along creeks and river bottoms--many, they can do a number to help with landclearing.
Canadian Thistle they attack when it blooms--usually the stage when a producer is having fits--they actually peel the stock and stress the thistle badly. The next year it is stunted in growth and they repeat the same deal; the 3rd year seems to be the killer....the thistle doesn't grow very high and when it tries to bloom, the goats finish it off.
A number of weed districts in Montana brought truckloads of Angora and spanish goats in from Texas....they were ok with the weeds but didn't have a plan for excess animals or the mohair as it regars Angoras...and predation is terrible--unless you plan ahead.