Finger grass (Digitaria species) is a common warm-season annual weed that often invades lawns. It thrives in thin, stressed turf, producing large amounts of seed that ensure its return year after year. Controlling this persistent weed requires a comprehensive strategy that moves beyond simple spot treatments. This guide details immediate removal methods combined with long-term prevention strategies for effective management.
Identifying Finger Grass
The first step in effective weed management is confirming the intruder is finger grass, also known as crabgrass. This warm-season annual grows from a central point, forming low, dense clumps that contrast noticeably with the surrounding turf. Its leaf blades are typically wider and flatter than desirable lawn grasses, often displaying a lighter, lime-green color.
The common name derives from its distinctive seed head structure, which emerges on stems above the foliage later in the season. These seed heads feature several thin branches, or racemes, that radiate outward from the stem, resembling the fingers of a hand. Young finger grass plants (two or three leaves) are significantly easier to control than mature plants that have developed multiple side shoots, known as tillers.
Post-Emergent Control Methods
Addressing a current finger grass infestation requires immediate action using physical removal or targeted chemical treatments. Manual removal is a practical solution for small, isolated patches or younger plants that have not yet established a strong root system. Pulling the weed is most successful when the soil is moist, which helps ensure the entire root crown is extracted.
For larger, widespread infestations, selective post-emergent herbicides offer a more efficient solution. Products containing the active ingredient Quinclorac are highly effective against many Digitaria species. This systemic herbicide acts as a synthetic auxin, disrupting the plant’s growth hormones. It is absorbed by the foliage and translocated throughout the plant, causing abnormal growth, chlorosis, and eventual death.
The timing of chemical application is important. Quinclorac is most effective on very young plants or those that are already mature, having developed four or more tillers. Applying this treatment during an intermediate growth stage may result in poor control, often requiring a second application.
To maximize absorption into the waxy leaves, it is recommended to mix the herbicide with a methylated seed oil (MSO) surfactant. Application should be avoided when temperatures exceed 90 degrees Fahrenheit, as high heat can stress the turf and increase the risk of damage.
Pre-Emergent Prevention Strategies
The most effective way to eliminate finger grass is to stop its seeds from sprouting in the first place, which is the function of pre-emergent herbicides. These products create a chemical barrier in the top layer of the soil that inhibits seed germination. If a seed sprouts and penetrates this barrier, the chemical prevents the seedling from developing a viable root system, killing the plant before it emerges above ground.
The timing of this application is determined by soil temperature, not the calendar, and is the most important factor for success. Finger grass seeds begin to germinate when the soil temperature at a two-inch depth consistently maintains 55 degrees Fahrenheit for several consecutive days. Applying the pre-emergent product before this temperature threshold is reached ensures the barrier is in place before germination begins.
A traditional visual indicator that this window is approaching is the blooming of local plants, such as the forsythia shrub. Missing this window means the seeds may have already germinated, rendering the pre-emergent product useless. Both traditional chemical formulations (like prodiamine or dithiopyr) and natural alternatives (such as corn gluten meal) must be applied and watered in promptly to activate the barrier before germination commences.
Cultural Practices for Long-Term Suppression
Maintaining a dense, healthy lawn is the foundation of long-term finger grass suppression, as thick turf naturally crowds out the weed. One impactful cultural practice is adjusting the mowing height to between 3 and 4 inches. Taller grass blades create shade over the soil surface, which keeps the soil cooler and prevents finger grass seeds from receiving the light required for germination.
Adjusting watering habits also favors turf grass over the shallow-rooted finger grass. Instead of watering lightly and frequently, which keeps the topsoil moist and encourages weed growth, the lawn should be watered deeply and infrequently. This method encourages the turf grass to develop deep, robust root systems, making it more competitive against the weed. Established lawns typically require about one to one and a half inches of water per week from rain or irrigation.
Proper soil nutrition and aeration further support a healthy turf canopy, which is the ultimate defense against weed encroachment. Core aeration relieves soil compaction, allowing water and nutrients to penetrate the root zone more effectively. Combining an appropriate fertilization schedule with high mowing and deep watering makes the turf dense enough to naturally suppress the germination and establishment of new finger grass plants.