Creeping bentgrass (Agrostis stolonifera) is a highly invasive, low-growing perennial weed that often appears in home lawns, where it is frequently mistaken for desirable turfgrass. This cool-season grass is a significant problem due to its aggressive spreading habit, which quickly creates unsightly, dense patches that disrupt the uniformity of a lawn. Successfully eradicating this weed requires a strategic, multi-step approach that combines both physical and chemical control methods.
Identifying Creeping Bentgrass
Creeping bentgrass can be identified by visual characteristics that set it apart from typical turfgrasses. It possesses a very fine, bright, or bluish-green texture, often appearing lighter in color than the surrounding lawn species. This contrast in color makes the patches highly noticeable, especially when the grass is actively growing.
The most defining feature is its aggressive, above-ground runners, known as stolons, which root quickly as they creep along the soil surface. These stolons allow the grass to spread rapidly and form dense, puffy, circular patches that can tolerate an extremely low mowing height. This growth habit, combined with its shallow root system, makes it difficult to control in established lawns.
Non-Chemical Removal Methods
For homeowners dealing with small, isolated patches, manual removal is a non-chemical option. This method requires digging out the entire patch, ensuring that all above-ground stolons and the shallow root structure are completely removed. Because bentgrass can regrow from even small fragments of stolons left behind, it is necessary to excavate an area slightly larger than the visible patch itself.
When the infestation covers larger, defined areas, solarization can be employed to kill the grass using heat. This technique involves covering the entire bentgrass patch with clear plastic sheeting, which traps solar energy and raises the soil temperature to lethal levels. The plastic should be left in place for approximately one week during intense sunlight to ensure the grass is killed. After the area is cleared, the dead turf must be raked out before reseeding or resodding.
Selective Herbicide Treatments
Chemical intervention is often the most effective solution for widespread or scattered creeping bentgrass. The most common active ingredient used for selective control in cool-season lawns is mesotrione, often sold under the trade name Tenacity. This systemic herbicide works by inhibiting the plant’s ability to create protective pigments necessary for photosynthesis, causing the bentgrass to turn white and eventually die.
Mesotrione is selective, meaning it can be applied to desirable cool-season grasses like Kentucky bluegrass or fescue without causing permanent damage. Multiple applications are necessary for effective control, typically requiring two to four treatments spaced two to three weeks apart. A temporary side effect of mesotrione is a noticeable bleaching or whitening of the treated bentgrass and sometimes the surrounding desirable turf, which usually appears five to seven days after application.
The ideal time for application is when the bentgrass is actively growing, usually in the late summer or early fall, as this timing allows for subsequent overseeding of the treated areas. For areas with solid bentgrass patches, a non-selective herbicide containing glyphosate can be used for complete spot killing. This option will kill all vegetation it contacts, necessitating immediate reseeding or sod replacement once the target grass is dead.
Lawn Recovery and Long-Term Prevention
After the creeping bentgrass has been killed, the priority is to restore bare or thinned areas by overseeding with desirable turfgrass varieties. Overseeding in the late summer or early fall is optimal, as cooler temperatures and less competition from summer weeds aid in seed establishment. Core aeration before seeding helps prepare the soil and improve seed-to-soil contact, promoting faster germination and turf density.
Long-term prevention relies on modifying cultural practices to favor the desirable turf. Raising the mowing height to at least two and a half to three inches discourages the low-growing bentgrass from thriving. Deep, infrequent watering is also recommended, as this encourages the desirable turf to develop a deeper root system, while the shallow-rooted bentgrass is stressed by drier surface soil. Proper fertilization, particularly avoiding excessive nitrogen applications during hot summer months, helps maintain a healthy stand of turf that can naturally outcompete new bentgrass growth.