The idea behind pre-emergent lawn treatments is to make the area inhospitable for grassy weeds, like crabgrass and foxtail before they can take root in the soil. Right now, when mother nature is warming up the earth is precisely when these weeds start to wake from their winter hibernation. Once your lawn reaches ___ degrees, consider the welcome sign illuminated. Make sure you hit them with a good quality pre-emergent treatment before they move in for good.