Crabgrass presents a unique challenge in Bermuda grass lawns because both are warm-season grasses. This similarity means that many broad-spectrum weed killers designed to eliminate grassy weeds will also harm the desirable Bermuda turf. Crabgrass, an annual weed, germinates prolifically in the spring and grows aggressively throughout the summer, outcompeting the Bermuda grass for sun, water, and nutrients. Successfully controlling this weed requires a two-pronged strategy: preventing emergence and selectively eliminating established plants without damaging the turf.
Preventing Crabgrass Germination
The most effective method for managing crabgrass is preventing its seeds from sprouting. This strategy relies on the precise timing of a pre-emergent herbicide application. Crabgrass germination begins when the soil temperature consistently reaches 55°F at a two-inch depth for several days.
The herbicide must be applied and watered into the soil before the temperature hits this threshold to create a chemical barrier that stops seed development. Applying too late, after germination has begun, renders the product ineffective, requiring a more aggressive chemical approach later. Common active ingredients safe for use on established Bermuda grass include prodiamine and pendimethalin. These compounds are mitotic inhibitors, disrupting cell division in the emerging roots of the weed seedling. While generally safe for established Bermuda grass, they can temporarily reduce root growth, so label rates must be followed strictly.
Eliminating Active Crabgrass
When prevention fails, the focus shifts to selective post-emergent control targeting established, visible crabgrass plants. This is challenging because the chemical must kill a grass-like weed while leaving the Bermuda grass unharmed. The standard for selectively killing mature crabgrass in Bermuda grass is the herbicide quinclorac.
Quinclorac is highly effective on crabgrass at various growth stages, from the newly germinated one-leaf stage to the mature five-tiller stage. To penetrate the waxy leaf surface of the crabgrass, it is often necessary to mix quinclorac with a non-ionic surfactant or methylated seed oil. This adjuvant helps the chemical adhere to and be absorbed by the weed for maximum effectiveness.
The application should occur when the crabgrass is actively growing, ideally when temperatures are between 65°F and 80°F. Applications during peak summer heat, especially above 85°F, can increase the risk of temporary injury to the Bermuda grass, such as slight discoloration. While quinclorac is the preferred treatment for larger plants, younger crabgrass may also be controlled with combination products containing chemicals like 2,4-D. For persistent or mature crabgrass, a second application of quinclorac may be required 14 to 21 days after the first treatment.
Strengthening Bermuda Grass for Long-Term Control
Chemical treatments provide immediate control, but long-term success requires promoting a dense, healthy stand of Bermuda grass that naturally outcompetes weeds. Bermuda grass is a vigorous grower, and cultural practices help it shade out germinating crabgrass seeds. Mowing height is a simple tool; while hybrid Bermuda is often cut very low (0.5 to 1.5 inches), raising the cutting height slightly helps shade the soil.
A dense turf canopy blocks the sunlight necessary for crabgrass seeds to sprout, creating a natural barrier. Watering practices should focus on deep and infrequent irrigation, which encourages the Bermuda grass to develop a deep, drought-tolerant root system. Applying 1 to 1.5 inches of water per week, all at once, is more beneficial than shallow, frequent watering, which promotes shallow roots.
Appropriate fertilization is important to maintain the vigor needed for competition. Bermuda grass requires a high amount of nitrogen during its active growing season to support rapid growth and density. A consistent feeding schedule helps the turf fill in bare spots quickly, removing the open soil that crabgrass prefers for germination. These practices support a resilient lawn, making it more difficult for the annual weed to establish itself.