A herbicide will kill it but it is a late germinating weed and it may only appear when you already have crops or surrounding plants actively growing. It is a prolific seed producer, as you probably know already, with the seedlings producing a very fine mat of roots that, if you wait until they are big enough to pull up, could well result in you pulling up crop plants too. As Palustris advises, hoeing is the best way. Do it as soon as the seedlings emerge and frequently thereafter.