Bent grass (Agrostis spp.) is a grass valued for the ultra-low mowing tolerance of golf course greens, but it becomes an unwelcome, persistent weed in a home lawn. This creeping species spreads aggressively, forming noticeable patches that disrupt the uniform texture of turf composed of Kentucky bluegrass, fescue, or ryegrass. Control involves a targeted, multi-step strategy combining cultural practices, manual labor for small infestations, and the precise application of specialized chemicals for long-term control.
Identifying Bent Grass and Understanding its Spread
Bent grass is typically identifiable by its distinct visual characteristics and growth pattern. It appears as fine-textured patches, often with a slightly lighter, brighter, or blue-green color compared to the surrounding turf. These patches create a puffy, spongy feel underfoot, especially when the lawn is mowed at a higher residential height.
The primary reason for its persistence is its vigorous reproductive structure: the stolon. Stolons are above-ground, horizontal stems that creep along the soil surface, rooting at the nodes to produce new plants. This matting growth habit allows bent grass to rapidly colonize bare soil or thin areas in the lawn.
Cultural and Manual Removal Techniques
For smaller, isolated patches, manual removal remains a viable option, though it requires meticulous attention to detail. This process involves carefully digging out the entire patch, extending the removal zone several inches beyond the visible perimeter. Bent grass stolons are extensive, and unseen runners can quickly lead to re-establishment if not completely extracted.
Cultural practices that favor the desired turf species while stressing bent grass are important for management. Bent grass thrives in consistently moist conditions and low mowing heights, so homeowners should adjust maintenance routines accordingly. Raising the mower deck to a height of three inches or more helps the taller, desired grass species shade out the low-growing bent grass stolons, discouraging its spread.
Adjusting irrigation schedules targets bent grass’s shallow root system. Watering deeply but infrequently encourages the desired turf to develop deeper, more drought-tolerant roots. This intentionally stresses the bent grass, which has roots closer to the surface and prefers daily or near-daily moisture. Reducing nitrogen fertilization is also beneficial, as an excess favors the rapid, dense growth of bent grass over other cool-season turf.
Targeted Chemical Treatment Options
Chemical intervention is often necessary for larger, more established infestations of bent grass. The most effective approach involves using selective herbicides that target the invasive grass while sparing the surrounding desirable turf. Products containing the active ingredient mesotrione are recommended for this purpose.
Mesotrione works by interfering with the plant’s photosynthesis process, causing the bent grass to turn a noticeable white color a few days after application. This bleaching effect indicates the chemical is working, and the grass will subsequently die off. For successful control, multiple applications are required, typically two to three treatments spaced two to three weeks apart, with the first application often starting in mid to late summer when the bent grass is actively growing. Applying mesotrione with a non-ionic surfactant is often necessary to improve absorption and overall efficacy.
If the bent grass infestation is extremely dense, or if the homeowner is prepared for a full renovation, a non-selective herbicide containing glyphosate may be used. This approach will kill all vegetation it contacts, including the desired lawn grasses. It is used for spot treatments where the target area is completely saturated to ensure the entire root and stolon system is eliminated. When using a non-selective product, spray a boundary about six inches beyond the visible patch to ensure all creeping stolons are addressed.
Lawn Recovery and Preventing Recurrence
After successfully eliminating the bent grass, the resulting bare spots must be repaired quickly to prevent new weeds from establishing. This process involves preparing the soil by removing dead plant material and lightly raking the area to expose the soil surface. Aerating the area before seeding can also help improve soil-to-seed contact.
Overseeding the treated area with a high-quality, regionally appropriate turfgrass seed is the next step in achieving a uniform lawn. A starter fertilizer should be applied at the time of seeding to promote healthy germination and establishment of the new grass. Long-term prevention is achieved by maintaining a dense, healthy turf canopy, which naturally crowds out opportunistic weeds.
Ongoing prevention relies heavily on maintaining the cultural practices that stress bent grass. This includes continuing to mow at a high setting and adhering to a deep, infrequent watering schedule. Annual core aeration helps manage thatch buildup and promotes better air and water movement in the soil. Consistent monitoring and immediate spot-treatment of any returning bent grass patches are necessary to prevent a widespread recurrence of the problem.