Bull Paspalum (Paspalum dilatatum or Paspalum setaceum) is a grass weed that plagues manicured turfgrass, residential lawns, and agricultural pastures across warm-season climates. Its presence is characterized by coarse, unsightly clumps. Because this species is a deep-rooted perennial, it establishes itself firmly and returns year after year. Understanding the plant’s unique physical traits and life cycle is the first step in developing an effective, long-term control strategy for this invasive species.
Identifying Bull Paspalum
The primary method for confirming the presence of Bull Paspalum is by closely examining its physical structure and growth habit, which differs noticeably from desirable turfgrass. This plant is a bunch-type grass, meaning it grows in dense, tough, spreading tufts rather than forming a uniform sod like Bermuda or Zoysia grass. The leaves are typically broad, up to a half-inch wide, and exhibit a prominent mid-vein running down the center of the blade.
The lower leaf sheaths are often somewhat hairy, though the blades themselves may be mostly smooth. The most unmistakable characteristic, however, is the seed head, which emerges on upright stems that can reach over three feet tall if left unmowed. These seed heads feature three to seven finger-like branches, known as racemes, that diverge from the main stalk, often forming a distinct V or Y shape.
The spikelets along these racemes are particularly noteworthy when infected by the ergot fungus, Claviceps paspali. This fungus causes the seed heads to become sticky and dark, often appearing black or purplish-black, which is why the plant is sometimes referred to as “sticky heads.”
Understanding Its Life Cycle and Growth
Bull Paspalum is a warm-season perennial grass. It does not die off completely in the winter; instead, its above-ground foliage turns brown and goes dormant, while the root structure remains alive underground. This deep, thick, fibrous root system, which includes short, tough rhizomes, allows the plant to survive cold temperatures and rapidly send up new shoots when soil temperatures rise in spring.
The plant is highly adapted to thrive during the summer months, tolerating both intense heat and drought conditions better than many common turfgrasses. Its growth is particularly favored by moisture, making it frequently found in areas with poor drainage, compacted soil, or those prone to waterlogging. This adaptability allows it to quickly colonize disturbed areas where the competition from other plants is weak.
Aggressive seed production contributes to its persistence, as a single mature plant can produce hundreds of thousands of seeds. These seeds are easily dispersed by water, mowing equipment, or adhering to clothing and animal fur. The seedlings can be slow to mature, often taking two to three years to flower, which means a significant seed bank can build up in the soil before the problem becomes obvious to the homeowner.
Effective Control Strategies
Cultural and Mechanical Control
Managing Bull Paspalum begins with non-chemical methods focused on physical removal and modifying the growing environment to favor desirable turf. Hand-pulling is effective, but only for young, small clumps that have not yet developed an extensive root system. For established plants, complete manual removal requires digging out the entire coarse clump, including the short, tough rhizomes and the deep fibrous roots, to prevent regrowth.
Adjusting cultural practices can also significantly reduce the weed’s ability to establish and spread. Mowing the lawn at the highest recommended height for the specific turfgrass species helps to shade the soil, reducing the light needed for Bull Paspalum seeds to germinate. Alleviating soil compaction through core aeration can improve drainage, which minimizes the moist conditions this weed prefers.
Chemical Control
Chemical treatment is necessary for widespread or mature infestations. Pre-emergent herbicides target the seeds before they sprout. Applying a pre-emergent product with active ingredients like prodiamine or dithiopyr in late winter or early spring, before soil temperatures consistently reach 55°F, can prevent new seedlings from establishing throughout the summer.
Post-emergent herbicides are required for established, mature plants, though they are more difficult to use selectively. Selective herbicides containing active ingredients such as MSMA (monosodium methanearsonate) are effective against Bull Paspalum, but their use is now restricted primarily to commercial turf areas like golf courses and sod farms. For homeowners, a non-selective herbicide like glyphosate can be used for spot treatment on individual clumps, but this will kill any surrounding desirable grass and should be applied carefully with a sponge or shielded sprayer to minimize damage.
Prevention
Prevention hinges on maintaining a dense, healthy turf that outcompetes the weed for resources. A vigorous stand of turfgrass limits the space and sunlight available for weed seeds to germinate and the seedlings to grow. Proper fertilization and irrigation schedules, tailored to the specific turf species, promote the density required to crowd out the weed. By combining strategic pre-emergent applications with cultural practices that favor the lawn, the environment becomes hostile to Bull Paspalum, preventing future infestations from taking hold.