Pre-emergent herbicides form a chemical barrier in the top layer of the soil to stop weeds before they emerge in your Bermuda grass lawn. This preventative approach is fundamental to maintaining a dense, healthy turf, eliminating competition for water, sunlight, and nutrients. Choosing the most effective product and applying it at the correct time offers season-long protection against annual weeds.
Understanding Pre-Emergent Action and Bermuda Tolerance
Pre-emergent herbicides do not kill weed seeds; instead, they work by preventing the establishment of the seedling after the seed has germinated. As the weed seed sprouts, its first root, or radicle, contacts the treated soil layer and absorbs the herbicide. This absorption disrupts cell division, effectively stopping the root and shoot development and causing the tiny seedling to die before it can emerge from the soil.
This mechanism highlights why timing is important, as the barrier must be in place before weed seeds begin to sprout. Established Bermuda grass is highly tolerant because it is a perennial warm-season turf that spreads primarily through runners (stolons) and underground stems (rhizomes). Since the herbicide only affects vulnerable, newly germinating seeds, pre-emergents can be safely applied to a healthy Bermuda lawn.
Top Recommended Active Ingredients for Bermuda Grass
Effective pre-emergent products for Bermuda grass utilize active ingredients from the dinitroaniline (DNA) chemical family. These chemicals inhibit mitosis, or cell division, in the germinating weed. The choice of ingredient often depends on the specific weeds targeted and the desired duration of control.
Prodiamine, often sold under the brand name Barricade, is considered an industry standard for Bermuda maintenance due to its long residual effect and cost-effectiveness. It provides excellent, long-lasting control against major grassy weeds like crabgrass and Poa annua (annual bluegrass). Its low solubility means it tends to stay concentrated in the upper soil layer longer, making it a reliable choice for season-long prevention.
Dithiopyr, commonly known as Dimension, is another highly recommended option that offers a unique advantage. While primarily a pre-emergent, Dithiopyr also provides limited early post-emergent control of crabgrass. This means it can stop young crabgrass seedlings shortly after they sprout, making it a forgiving option for users who may have missed the earliest application window.
Pendimethalin (Prowl) is similar to Prodiamine and Dithiopyr in its effectiveness against annual grasses and broadleaf weeds. It is safe for established Bermuda grass, though it is sometimes noted for its tendency to leave a temporary yellow stain on surfaces.
Crucial Timing: When to Apply Pre-Emergents
The success of a pre-emergent program hinges entirely on accurate timing, which is determined by soil temperature, not the calendar date. The goal is to have the chemical barrier fully activated just before target weed seeds begin to germinate. Using a soil thermometer or local extension data is the most reliable method for determining the proper application windows.
The Spring Application targets summer annual weeds, primarily crabgrass, which begins to germinate when the average soil temperature consistently reaches 55 degrees Fahrenheit. Apply the pre-emergent when the soil temperature is between 50 and 55 degrees Fahrenheit to ensure the barrier is established before the germination threshold is crossed. Since most products last only eight to twelve weeks, a split application is recommended to provide season-long control.
The Fall/Winter Application is specifically aimed at cool-season annual weeds, most notably Poa annua and winter broadleaf weeds like henbit and chickweed. These weeds germinate as soil temperatures cool down in late summer and early fall. The recommended timing for this application is when the soil temperature drops below 70 degrees Fahrenheit, typically between late August and October, depending on your geographic region.
Application Techniques and Avoiding Common Mistakes
Proper application is essential to ensure the herbicide barrier is uniform and activated correctly across the entire lawn area. Before applying, accurately calibrate your spreader to deliver the correct amount of product per square foot. Treating the entire lawn consistently is necessary, as skipping spots creates pathways for weed emergence.
After spreading the granular or liquid product, it must be watered in immediately with approximately half an inch of irrigation or rainfall. This dissolves the active ingredient and moves it into the topsoil layer where weed seeds germinate, activating the protective barrier. Failure to water in the product promptly renders the application ineffective.
A significant mistake to avoid is applying pre-emergent too close to any plan to seed or overseed the Bermuda grass. Pre-emergents prevent all seeds from germinating, including desirable grass seed. If you are seeding a new lawn or overseeding a thin area, you must wait for the pre-emergent’s residual activity to dissipate. This dissipation can take three to four months, depending on the product label.