Bermuda grass (Cynodon dactylon) is an aggressive, warm-season perennial often problematic in cooler-climate lawns. It spreads rapidly and can quickly invade turf composed of cool-season grasses like fescue or Kentucky bluegrass. Eliminating this invasive grass while protecting the desirable lawn requires selective chemical treatment, since non-selective herbicides would destroy the entire turf area. The goal is to specifically target and eradicate the Bermuda grass without causing significant harm to the surrounding grass.
Why Bermuda Grass is Difficult to Eradicate
The difficulty in removing Bermuda grass stems directly from its specialized growth structures, which allow it to store substantial energy reserves. This grass features two types of creeping stems: stolons, which are above-ground runners, and rhizomes, which are underground stems. Both structures are capable of rooting at the nodes and forming new plants, allowing for rapid and extensive lateral spread.
When leaf blades are killed, the plant draws on stored carbohydrates in its underground rhizomes to quickly regenerate new growth. This aggressive root system means treating only the surface growth is ineffective for long-term control. Fragmented pieces of rhizomes or stolons can sprout new plants, making single herbicide applications insufficient. Depleting the plant’s deep energy reserves necessitates a persistent, multi-application strategy.
Selective Herbicides for Removal
Selective control of Bermuda grass in cool-season turf relies on post-emergent herbicides that exploit metabolic differences. The most common chemical families are aryloxyphenoxypropionates (FOPs) and cyclohexanediones (DIMs), often called “grass-selective” herbicides. These chemicals, such as fluazifop-p-butyl or fenoxaprop-p-ethyl, inhibit a key enzyme in the fatty acid synthesis pathway of grasses, but desirable cool-season grasses possess a higher tolerance.
Another highly effective option is the active ingredient topramezone, which belongs to the triketone chemical class. Topramezone inhibits a plant enzyme involved in chlorophyll production, causing the Bermuda grass foliage to turn white or “bleach.” This bleaching effect means the plant cannot photosynthesize, forcing it to draw on its reserves.
The best results are often achieved by combining products, such as using topramezone with a growth regulator like triclopyr. This combination attacks the Bermuda grass through multiple mechanisms, increasing the systemic movement of the herbicide into the rhizomes. When selecting a product, confirm on the label that the herbicide is safe for the specific desirable grass, such as tall fescue or Kentucky bluegrass, to prevent widespread damage.
Application Timing and Strategy
Successful eradication requires a strategic series of applications timed to exploit the Bermuda grass’s biology. Herbicides must be applied when the Bermuda grass is actively growing, typically during the warm months of late spring through late summer. Spraying when the grass is stressed by drought or high temperatures reduces effectiveness, as the plant will not efficiently move the chemical throughout its system.
The strategy must involve sequential treatments rather than a single application, with follow-up sprays necessary to target new growth emerging from the rhizomes. Applications are typically spaced 2 to 4 weeks apart, allowing the plant enough time to recover slightly and move the herbicide throughout its network. A common regimen may involve three or more applications throughout the summer and fall until the plant’s energy stores are fully depleted.
Preparation is also important; mowing the lawn a few days before treatment ensures the Bermuda grass leaves are present to absorb the maximum amount of herbicide. To increase absorption and movement, a non-ionic surfactant or crop oil concentrate is often mixed with the herbicide solution. Applying the final treatment in the early fall can be particularly effective, as the plant is actively storing carbohydrates for winter survival, which helps draw the herbicide deep into the rhizomes.
Preventing Re-establishment
After chemical treatments kill the Bermuda grass, long-term prevention focuses on cultural practices that favor the desirable turf. A healthy, dense lawn is the best defense against weed re-establishment because it limits the sunlight and space available for new growth. Overseeding thinned areas with the desirable cool-season grass, such as tall fescue, creates a thick canopy that shades the soil.
Bermuda grass is intolerant of shade, meaning that a taller mowing height of 3.5 to 4 inches for the desirable grass will naturally suppress any residual runners. Promoting deep root growth in the desirable turf by watering deeply and infrequently will also help the lawn outcompete any surviving Bermuda grass. Using a pre-emergent herbicide in subsequent early spring seasons can help prevent the germination of any residual Bermuda grass seeds that may be present in the soil.