The invasion of a desirable fescue lawn by aggressive Bermuda grass is a common problem for homeowners in transition zones. Solving this issue requires understanding the fundamental differences between the two grass types to employ a strategy of selective control. Since both are grasses, a non-specific chemical application would destroy the entire lawn. Targeted methods exploit their biological vulnerabilities, using specialized herbicides and specific cultural practices to eliminate the warm-season intruder while preserving the cool-season turf.
Key Differences Between Bermuda Grass and Fescue
Selective elimination relies on the distinct biological processes of warm-season and cool-season grasses. Bermuda grass is a warm-season turf using C4 photosynthesis, thriving between 75°F and 95°F. Tall Fescue is a cool-season grass using C3 photosynthesis, performing best between 55°F and 75°F, and its growth slows during hot summer months.
The physical growth habit of each species also informs control strategies. Bermuda grass is highly aggressive, spreading rapidly through above-ground stolons and underground rhizomes, allowing it to quickly colonize open areas. Fescue is a bunch-type grass, expanding primarily by growing outward from the base, making it less invasive.
Selective Herbicides for Bermuda Control
Targeted control requires post-emergent, systemic herbicides designed to kill one grass species without harming another. These specialized “grass-on-grass” herbicides are necessary because common broadleaf weed killers are ineffective against grassy weeds like Bermuda. The choice of herbicide must exploit the metabolic differences between the C4 Bermuda grass and the C3 Fescue.
Systemic chemicals like Fenoxaprop-P-ethyl (Acclaim) and Fluazifop (Ornamec) are absorbed through the leaves and transported to the root structure. These chemicals work by inhibiting acetyl-CoA carboxylase (ACCase), an enzyme necessary for lipid synthesis in grassy weeds.
Topramezone (Pylex) is also effective, known for its potency against Bermuda grass and high selectivity for tall fescue. Mesotrione (Tenacity) is utilized, often combined with Triclopyr (Turflon). Mesotrione works by inhibiting the HPPD enzyme, causing the target plant’s foliage to turn white as it cannot produce protective carotenoids.
Effective removal requires multiple treatments, typically three to four applications spaced two to four weeks apart, to exhaust the plant’s underground energy reserves. Although fescue may show temporary discoloration, it possesses a higher tolerance and generally recovers fully. Always consult the product label for specific application rates and safety instructions to minimize harm to the desirable turf.
Cultural Practices That Favor Fescue
Chemical control must be combined with specific lawn maintenance practices that optimize conditions for fescue and stress Bermuda grass. Fescue thrives when mowed high, ideally maintaining a height between three and four inches. This taller canopy shades the soil surface, suppressing the growth of sun-loving Bermuda grass, which requires intense light exposure.
Irrigation is another tool; fescue has a deeper root system than Bermuda grass, allowing it to tolerate deep, infrequent watering. Watering deeply, only when the grass shows signs of drought stress, encourages fescue roots to grow deeper. The lack of frequent surface moisture stresses the shallower-rooted Bermuda, and reducing water in the heat of summer can cause severe dieback.
Fertilizer timing also plays a part by feeding the desired grass during its peak growth period. Fescue benefits most from fertilization in the fall and early spring. Avoiding heavy nitrogen applications during the hot summer months prevents boosting the growth and spread of the warm-season Bermuda grass.
Application Timing and Lawn Repair
The schedule for applying selective herbicides is the most important factor for maximizing effectiveness. The best time to begin treatment is in the late summer, typically mid-August through September, when Bermuda grass is actively growing but preparing for winter dormancy. During this period, the plant naturally moves carbohydrates and nutrients to its rhizomes and stolons for storage. Applying a systemic herbicide ensures the chemical is translocated deep into the underground structures, resulting in a more complete kill. Follow-up applications must continue on a two to four-week schedule until the invasive grass is eliminated or enters full dormancy.
Once the Bermuda grass has died back, bare patches need to be addressed promptly. The ideal time for lawn repair is the fall, immediately following the final herbicide application. Overseeding with Tall Fescue seed allows the new grass to establish a robust root system before winter, giving the fescue a competitive advantage over any surviving Bermuda grass the following spring.