Bentgrass is an aggressive grass that is commonly used on putting greens. Allowed to grow out, it becomes matted and scraggly. Bentgrass invades lawns, crowding out desirable grasses.
Unless you practice golf in your yard, bentgrass isn't something you want around. Kept very short, it looks neat and uniform. Allowed to grow, it forms dense, scraggly mats. Bentgrass is very invasive and crowds out desirable lawn grasses. You can treat it with a product such as Round Up® Weed & Grass Killer.
Treat bentgrass patches with a grass control during the summer, when the weed is actively growing. Be careful spraying, since most treatments for bentgrass will also kill the grass you want. One week after spraying, mow the area short and reseed.