Bull Paspalum, often a collective term for aggressive perennial species like Paspalum setaceum or Paspalum dilatatum (Dallisgrass), represents a significant challenge in maintaining turf and landscape areas. This warm-season grass weed forms unsightly, coarse clumps that aggressively compete with desirable turf for water and nutrients. Control is difficult because the plant establishes a deep, robust root system and short, tough rhizomes, while producing vast quantities of seed. Successfully managing this weed requires a comprehensive strategy targeting both established perennial plants and germinating seedlings.
Visual Identification Markers
Positive identification of Bull Paspalum begins with observing its characteristic growth habit and foliage. The plant typically forms a flat, dense, clumping structure, with stems leaning outward from a central crown, creating a coarse texture in fine turf. Its leaves are flat, often having a prominent mid-vein, and can appear dull blue-green to dark green, sometimes with a purplish tinge at the base of the stems.
A defining feature is the collar region, which often exhibits a short, membranous ligule fringed with fine hairs. The leaf sheaths are loose and smooth, but the blade margins are sparsely hairy, distinguishing it from other grassy weeds. The most recognizable marker is the seed head, which emerges on slender stalks in mid-to-late summer. It displays two to eleven finger-like branches arranged alternately along the main stem, carrying small, oval-shaped spikelets in pairs that are prolific seed producers.
Growth and Reproductive Cycle
Bull Paspalum is classified as a C4 warm-season perennial grass, meaning its growth is most vigorous during the hottest months. It remains dormant during winter, with the foliage turning brown, but underground structures persist. This allows it to regrow when soil temperatures consistently rise in spring. This perennial nature, supported by a dense, fibrous root system and short, creeping rhizomes, makes established clumps extremely difficult to remove entirely.
The plant employs a dual reproductive strategy, relying on both its perennial root structure and the prolific production of seeds. Flowering and seed set typically begin in mid-summer and continue into autumn, with a single mature plant capable of generating hundreds of thousands of seeds. Since these seeds require warm, moist conditions to germinate, new infestations occur throughout the summer growing season. Effective control must target both the established clumps regrowing from rhizomes and the continuous germination of new seedlings from the seed bank.
Non-Chemical and Cultural Management
Cultural practices are the first line of defense against Bull Paspalum, focusing on maintaining a dense, healthy turf that naturally suppresses weed growth. Adjusting the mowing height to the upper limit recommended for the specific turfgrass species is an effective strategy. This allows the grass to shade the soil surface, reducing the light available to Bull Paspalum seeds and inhibiting germination.
Proper irrigation is also important, as the weed thrives in moist conditions, particularly where water accumulates. Deep, infrequent watering encourages the turf’s roots to grow deeper while discouraging the shallow, surface-level growth favored by the weed. When seed heads begin to appear, mowing regularly and collecting the clippings prevents the maturation and dispersal of seeds into the soil.
Mechanical Removal
For small, isolated patches, mechanical removal is a practical solution, though it requires meticulous effort due to the deep root structure. The entire clump, including the dense crown and all associated rhizomes and roots, must be completely dug out using a trowel or spade to prevent regrowth. If even a small portion of the perennial crown or a rhizome fragment remains, the plant can regenerate within a few weeks, making follow-up monitoring essential.
Barrier Methods
In areas of severe infestation, especially in non-turf areas or before laying new sod, barrier methods can be employed. Applying a thick layer of organic mulch in landscape beds suppresses seed germination by blocking light and creating a physical barrier. For large, bare areas, solarization—covering the area with clear plastic sheeting during the hottest months—can raise soil temperatures high enough to kill both seeds and established rhizomes.
Targeted Herbicide Control Strategies
Chemical control strategies involve a combination of pre-emergent and post-emergent herbicides, which must be carefully selected based on the desired turf species. Pre-emergent herbicides prevent new infestations by controlling Bull Paspalum seeds before they germinate in the warm, moist soil. Products containing active ingredients like prodiamine or pendimethalin should be applied in early spring, before soil temperatures reach the threshold for weed seed germination, to establish a chemical barrier.
Post-emergent control targets established, actively growing Bull Paspalum clumps that have survived the winter. Historically, the most effective active ingredient has been Monosodium Methane Arsonate (MSMA), a selective herbicide often restricted to use on golf courses or sod farms due to toxicity concerns. For residential and commercial turf, professional-grade selective herbicides are needed, often containing sulfonylurea compounds.
Active ingredients such as sulfosulfuron (e.g., Certainty) or flazasulfuron (e.g., Katana) offer selective control in many warm-season turf types, including Bermuda and Zoysia grass. These systemic herbicides are absorbed by the foliage and translocated to the roots and rhizomes. They require multiple applications, typically spaced three to four weeks apart, to completely exhaust the perennial root system. Some turf species, like St. Augustine and Centipede grass, are sensitive to these products, making herbicides like metsulfuron a safer alternative. Always read the product label entirely before application, as it specifies the correct application rate, safe turfgrass species, and necessary safety precautions.