The best weed killer for existing lawns is a herbicide that won't affect the grass, such as 2,4-D, which kills only broadleaf plants, or pendimethalin, which controls crabgrass. The harshest weed killer is a non-selective herbicide, which kills all vegetation and is best if you are reseeding.
About this Author
Thomas K. Arnold is the publisher and editorial director of Home Media Magazine and a regular contributor on entertainment to "USA Today", "The Hollywood Reporter," "San Diego Magazine" and other publications.
An alumnus of San Diego State University, Arnold has appeared on such TV shows as "CNN", "E! Entertainment" and "G4's Attack of the Show" to discuss home entertainment and technology issues.