Any undesirable species of grass growing in a lawn is a weed. Grassy weeds are some of the most difficult types of weeds to control because they have many of the same growing characteristics as the desirable grass. Most herbicides that kill grassy weeds also damage the lawn turf. Control options include pulling the weeds by hand or killing the entire lawn and establishing a new one without the weeds.
Weedy grasses often have a different color, height or texture than the majority of the turf grass. If they are the only plants growing, they are not a problem. However, when they cause contrast with the remainder of the turf, they are a problem. If the homeowner chooses to try to eliminate these weeds by hand, it is essential to remove all the vegetative matter from the weeds. Many have underground rhizomes that form new plants from very small portions.
Biologists divide grassy weeds into annuals and perennials. Annual weeds generally appear later in the season and are easier to control than perennials. Perennial weeds develop a green color and begin growing early in the season.
If planning to reseed a lawn, time the killing of the grass to occur in the mid to late growing season. Landscapers should plant the new seed several weeks before the first frost to establish the new lawn before the dormant period.