Use Spectracide Weed Stop For Lawns Plus Crabgrass Killer Concentrate, 40 ounces to kill over 470 types of weeds as listed, including crabgrass. The product kills by contact, producing visible results in 5 hours. This product kills down to the root, and when used as directed, kills listed weeds including crabgrass not the lawn. This product kills all types of listed broadleaf and grassy weeds including dandelion, chickweed and clover as well as crabgrass and yellow nutsedge see product label for complete list of weed types. Apply when daytime temperatures are between 45°F and 90°F. Do not apply to Bermudagrass when daytime temperatures exceed 90°F. For best results, mow lawn two to three days before treating.