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Publication #ENH1132

Tropical Signalgrass Biology and Management in Turf1

J. B. Unruh, D. E. Partridge-Telenko and B. J. Brecke2

Tropical signalgrass (Urochloa subquadripara), also known as small flowered alexandergrass, has become one of the most troublesome weeds in the southeastern turfgrass industry and is especially problematic in sod production. Tropical signalgrass is a warm-season perennial that is propagated by seed and stolons. Stems are usually trailing and creeping, rooting at the nodes. Leaf blades are flat, 0.3 to 0.5 in. wide and up to 0.75 in. in length. Both the leaf blade and sheath are hairy and the ligule has a short fringe of hairs. Flowering branches may reach 18 inches tall and produce two to seven branches or “fingers” in the raceme of the seedhead (Fig 1). In the field, tropical signalgrass germination occurs when soil temperatures reach 77°F (Fig 2). A soil pH of 5 to 6, which is common in Florida soils, is required for germination. Moisture is required for seed germination, and the typical dry season in Florida can delay tropical signalgrass infestation.

Preemergence application of benefin +oryzalin, benefin +trifluralin, dithiopyr, imazaquin and oryzalin will control tropical signalgrass up to 8 weeks after application.

Early postemergence application of asulam, metribuzin or quinclorac will provide moderate control of tropical signalgrass when applied before the 8-leaf stage. Most selective postemergence herbicides will not control mature tropical signalgrass. Non-selective spot control of tropical signalgrass can be accomplished by making multiple spot-treatment applications of glyphosate with a preemergence herbicide such as pendimethalin added to the mix. This treatment will also kill the turfgrass, but will help minimize future tropical signalgrass populations.

There is no management program available that will completely control tropical signalgrass, but using an integrated weed management program will help reduce tropical signalgrass in the long-term.

Tropical signalgrass infestation can be minimized by careful mapping of infested areas and recording spray applications for proper herbicide timings and applications. Sanitation practices that include rinsing mowers between fields, controlling tropical signalgrass in ditches, minimizing unnecessary traffic in fields, and sprigging with weed-free stock will help minimize spread into non-infested areas. Before applying any product, refer to its label for specific application information and turfgrass tolerance.

Tropical signalgrass. 

Predicted Tropical Signalgrass Emergence. 

Tropical signalgrass. 

Herbicide options for controlling tropical signalgrass in Florida turfgrass

(Always refer to the label for specific uses, application rates and turfgrass tolerance)

Refer to the publication, Pest Control Guide for Turfgrass Management at turf.ufl.edu for brand names associated with chemical names listed.

Bermudagrass

  • Preemergence: benefin + oryzalin, benefin + trifluralin, dithiopyr, metolachlor, oryzalin and prodiamine

  • Postemergence: none

St. Augustinegrass

  • Preemergence: benefin + oryzalin, benefin + trifluralin, dithiopyr, metolachlor, oryzalin and prodiamine

  • Postemergence: asulam (sod production only)

Centipedegrass

  • Preemergence: benefin + oryzalin, benefin + trifluralin, dithiopyr, metolachlor, oryzalin and prodiamine

  • Postemergence: sethoxydim

Bahiagrass

  • Preemergence: benefin + oryzalin, benefin + trifluralin, dithiopyr, metolachlor, oryzalin and prodiamine

  • Postemergence: none

Seashore paspalum

  • Preemergence: dithiopyr and prodiamine

  • Postemergence: none

Zoysiagrass

  • Preemergence: benefin + oryzalin, benefin + trifluralin, dithiopyr, metolachlor, oryzalin and prodiamine

  • Postemergence: fenoxaprop, fluazifop

Perennial ryegrass

  • Preemergence: benefin + oryzalin, benefin + trifluralin, dithiopyr

  • Postemergence: none

Citation

Teuton, T. C., C. L. Main, T. C. Mueller, J. B. Wilkerson, B. J. Brecke, J. B. Unruh. 2005. Prediction modeling for tropical signalgrass (Urochloa subquadripara) emergence in Florida. Online. Applied Turfgrass Science doi:10.1094/ATS-2005-0425-01-BR.

Footnotes

1.

This document is ENH1132, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date June, 2009. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.

2.

J. Bryan Unruh, associate professor, Environmental Horticulture Department; Darcy E. Partridge-Telenko, postdoctoral research associate; and Barry J. Brecke, professor, Agronomy Department; West Florida Research and Education Center, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.