Any grass in a lawn that is undesirable is a weed grass. Actually, there are several undesirable grasses that can invade the home turf.
Bentgrass is great for the golf green. It is noticeable for its very fine-textured blades, light green colour and above ground stems that often lie flat on the soil surface. Often you will find that the stems lying on the surface will have roots starting to grow on them. Bentgrass is used extensively on the golf green because it will tolerate being cut very short.
Bentgrass is a problem on home lawns because it is shallow rooted and thus requires a great deal of pampering. It is easily damaged in the winter and then takes much longer to green up in the spring. With shallow roots, it does not have the ability to draw moisture from deep in the soil, and tends to turn brown with the hot, dry weather. The stems often turn brown, exposing dead areas when the lawn is mowed. Bentgrass grows vigorously and will spread very quickly in home lawns.
Control of Bentgrass:
As with quackgrass, there aren't any products that selectively control bentgrass. If you find a small patch, remove the grass and resod. If you have more than you care to dig up, rake hard in the spring to remove as much as possible. Set your mower up hight- at least 2 1/2 inches. When your lawn is mowed short, bentgrass is better able to tolerate the close mowing than Kentucky Bluegrass for instance. Use an infrequent watering routine as this will discourage the shallow-rooted bentgrass. If there is a lot of bentgrass creating a new lawn is the only way to get rid of bentgrass. Incidentally, when mowing, mow the areas with bentgrass last. Small pieces of bentgrass will root in other areas if the right amount of moisture is available.
See also Bent Grass Questions
If you have a lawn/tree/shrub that needs some Tender Loving Care- get The KING OF GREEN: