Crabgrass is a grass, not a weed. Therefore, it is not controlled by traditional weed control. This is a very invasive grass that starts to germinate in late spring. It is a light colour green that grows in direct sun, usually where the turf is thin or along the edges of drives or walks. It spreads rapidly from there. Later in August/ September it will turn purple as it goes to seed and then the mature plant dies when the frost arrives. Unfortunately, the seeds have already been planted in the soil. In the spring, these areas will be muddy dead patches because last year’s plant has died. However, when the soil gets warm enough, the seeds will germinate and the crabgrass takes over more and more of your lawn and chokes out your grass.