For established lawns, think back to the previous season. If you had a crabgrass problem in your lawn last year, you should consider adding a crabgrass control product to your maintenance program this season. Crabgrass plants are very prolific seed producers and all that seed remains viable in the soil for years. If you have used crabgrass control for two years and your lawn is dense and healthy, chances are you could alternate years between a straight fertilizer and a control program. For newly seeded lawns, it is a good practice to apply a pre-emergent crabgrass control product with Tupersan at the time of seeding and approximately two weeks later. This would help keep crabgrass populations in check and allow your lawn to fill in the area without excess competition.