I don't know of any easy way to keep these things cleaned up. How would you like to share some of these seedlings or seeds? I would love some to get them growing in my back acerage. Let us know.
I have them also in my back yard and the only way I can prevent them from growing is to lay down that weed blocker in my veg and flower beds as early as possible. Frankly, I leave them there for the entire season as I work alot of overtime and don't have time to pull weeds constantly.