Roundup Ready-to-Use Poison Ivy Plus Tough Brush Killer can take up to 2 weeks to completely kill sprayed weeds. Some perennial weeds such as poison ivy can take up to 4 weeks or more to completely kill. For the best results, just spray the product on the target area until the weeds are thoroughly wet and apply the product when the weeds are actively sprouting and during calm, sunny, and warm days
