Spectracide Weed Stop For Lawns Concentrate controls more than 200 types of weeds as listed ? and it won't harm your lawn when used as directed. This concentrated formula kills down to the root, with overnight results. It controls all major broadleaf weeds, including dandelion, chickweed and clover (see product label for complete list). This product is rainfast in 6 hours, so it won't wash off. For best results, mow before treating weeds with Spectracide Weed Stop For Lawns Concentrate. Spray in spring when weeds are small and growing, or in fall when many problem weeds germinate ? treating in fall will eliminate many of next year's weeds. If certain tough weeds are not dead within 3 weeks, repeat spot treatment. Read the entire label before using.