One reviewer noted that Preen isn't a crabgrass killer but a preventer. The implication is that this product, even as a sometimes post-emergent treatment, isn't meant to deal with a lawn full of ...

Start crabgrass control in February to prevent its spread; 50 to 60 degrees Fahrenheit is its germination range. Apply pre-emergent herbicide in February, maintain a neat lawn, and use post ...