Preemergence is effective in controlling summer annual weeds and certain annual broadleaf weeds. The length of control depends on the specific product being used, soil, physical and chemical properties, soil moisture levels, and soil temperatures. Preemergence can be most effective on Crabgrass if it is applied before the seed germination process. Crabgrass initiates spring germination when soil temperatures at a 4-inch depth reach 53 to 58 degrees F. This can occur from mid-February to April in most areas of the southeastern United States. Unique Environmental Landscape’s rule of thumb is to start application of the preemergence herbicide in late January through February. Unique then applies a combination of preemergence and postemergence in late March through early April to catch in weed seeds that may have germinated.
Warning: If you sodded in late fall or winter with Bermuda or Zoysia, do not apply a preemergence until after ‘green up’ of the turf. The grass should be actively growing so the the root is not damaged by the preemergence.