Milford from Waterman, Il writes
Ferti-Lome Weed Out with Crabgrass Killer will not prevent crabgrass from germinating but will eradicate crabgrass that is actively emerging/growing but not past mid July as the crabgrass will be too mature and more difficult to eliminate. Please contact your local cooperative extension office for specific timing in your area. We recommend that you apply a pre-emergent herbicide such as Prodiamine to prevent it from emerging.
Answer last updated on: 02/25/2017