Bermuda grass invading a Fescue lawn is a common turf management challenge. This issue is complicated because Bermuda grass is a warm-season grass that aggressively spreads using runners, while Fescue is a cool-season, bunch-type grass. Eliminating one species without damaging the other limits the use of broad-spectrum chemical solutions. Successfully removing the invader requires a multi-year strategy combining cultural practices that favor Fescue with carefully timed applications of selective herbicides.
Confirming It Is Bermuda Grass
Accurate identification is the first step, as misidentifying the grass leads to ineffective treatments. Bermuda grass (Cynodon dactylon) is recognized by its growth habit using both above-ground runners (stolons) and below-ground runners (rhizomes), allowing it to spread quickly and colonize bare soil. These runners root down at the nodes, creating a dense, mat-like growth pattern. The leaf blades are typically fine-textured, grayish-green, and feature a distinct V-shaped tip.
In contrast, Tall Fescue (Festuca arundinacea) is a bunch-type grass that expands by growing new shoots from the base of the plant. Fescue blades are characteristically wider and flatter, with parallel veins, and the overall color is generally a deeper green. If a fine-bladed grass is spreading across the soil surface during the heat of summer, it is likely Bermuda grass.
Cultural Methods to Suppress Growth
Implementing cultural practices that favor Fescue turf significantly enhances the effectiveness of chemical treatments. Bermuda grass is a C4 plant that thrives in full sun and high temperatures but cannot tolerate low light conditions. The primary cultural defense is maximizing the Fescue’s height to create shade.
Raise the mowing height to between 3 and 4 inches, which is the upper end of the recommended range for Fescue. This increased canopy height intercepts sunlight, shading the soil surface and suppressing the growth of Bermuda grass. Maintaining a 4-inch height can help eliminate Bermuda grass because the invader is starved of the light energy it requires.
Adjusting watering and fertilization schedules also helps weaken the warm-season Bermuda grass. Fescue should be watered deeply and infrequently to encourage deep root growth. Nitrogen fertilization should support Fescue’s peak growth periods in the fall and early spring. Avoid heavy feeding in the hot summer months, as this primarily benefits the Bermuda grass. By consistently prioritizing Fescue’s needs, the desirable grass gains a competitive advantage.
Using Selective Herbicides for Removal
Chemical control is necessary for significant Bermuda grass infestations, requiring highly selective herbicides that target the unwanted grass while leaving the Fescue unharmed. These chemicals are absorbed by the leaf tissue and translocated to the runners and roots, disrupting the plant’s growth mechanisms.
The most effective active ingredients include:
- Fenoxaprop-P-ethyl
- Fluazifop-P-butyl
- Topramezone
- Triclopyr
Application timing is crucial for maximum efficacy and Fescue safety. The best time to apply the herbicide is when the Bermuda grass is actively growing and healthy, typically from late spring through mid-summer. Temperatures should be consistently above \(70^{\circ} \text{F}\) but below \(85^{\circ} \text{F}\). Avoid application during periods of extreme heat or drought stress, as this harms the Fescue and reduces chemical absorption. A non-ionic surfactant must be added to the spray solution to help the herbicide adhere to the waxy leaf surface.
A single application will not eliminate Bermuda grass due to its extensive network of rhizomes and stolons. A treatment program generally requires two to four applications, spaced 10 to 21 days apart, to exhaust the plant’s underground energy reserves. Wait at least three days after mowing to allow for sufficient leaf area to absorb the product, and do not mow again for two days after application. These herbicides may cause temporary discoloration in the Fescue, but the grass should recover within 10 to 14 days. Always follow the specific product label instructions.
Lawn Recovery and Preventing Recurrence
Once the Bermuda grass has been chemically suppressed, the resulting dead patches must be addressed. The most appropriate time for lawn repair is during the Fescue’s peak growing season, typically late summer to early fall. Overseeding the damaged areas with high-quality Tall Fescue seed will fill in the voids left by the dying Bermuda grass, re-establishing a dense turf barrier.
Before seeding, core aeration can be performed to relieve soil compaction and improve seed-to-soil contact, increasing the germination rate. Note that some herbicides, such as triclopyr, may impose a seeding restriction of three weeks or more; consult the product label before planting. Successful recovery depends on maintaining consistent moisture for the new seedlings during establishment.
Long-term prevention relies on maintaining cultural practices that suppress Bermuda grass growth, especially the high mowing height. Address any new patches of Bermuda grass immediately with spot treatments of a selective herbicide before the infestation spreads. If the source of the invasion is an adjacent lawn, consider installing a physical barrier, such as landscape edging buried a few inches into the soil, along property lines.