Roundup Concentrate Extended Control Weed & Grass Killer Plus Weed Preventer is a double action, non-selective herbicide that kills prevailing weeds and grasses all the way to their roots. The product's formula keeps fresh weeds from developing, as long as 4 months, by penetrating deep into the ground and keeping any weeds from taking root. The product is not recommended for spot weed control in lawns since the active ingredient (glyphosate) kills grasses. For best results, apply the product when the weeds are actively sprouting and during calm, sunny, and warm days, where the temperature is above 60°F. Rainproof in 10 minutes and showing visible results in 3 hours, the product makes it easy to kill any problem weeds on your property.