Answer: Your landscapers probably failed to use a pre-emergent herbicide before laying the weed barrier. Pre-emergents will stop weed seeds from germinating. The best course of action is to hand pull the existing crabgrass and then apply a pre-emergent such as Preen (there are other brands available). Pre-emergents will stop future weeds but won't kill existing weeds. It's best to pull the crabgrass before it goes to seed. Best wishes with your landscape!
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