Dallisgrass (Paspalum dilatatum L.) is a perennial, warm-season grassy weed common throughout Louisiana. It is typically found growing in lawn areas with dry, compacted soils. Dallisgrass has coarsely textured leaves and stems that form unsightly clumps in turfgrass. It spreads primarily by rhizomes (underground stems) or seeds. Seeds germinate in the spring and summer to form new clumps. As dallisgrass becomes more established in a lawn, it is more difficult to control.
Dallisgrass has gray-green, coarsely textured leaves with a distinct mid-vein. Tiny black flowers grow on spikes (stems of clustered flowers), which are alternately attached to the flower stem. Its spikes are oriented in a flat, nearly two-dimensional manner on the flower stem, as opposed to being whorled around it like other grass seed heads. Dallisgrass has short, thick, brown rhizomes (underground stems) with distinctive rings.
For more information on Dallisgrass identification and characterization visit the USDA Plants Database at https://plants.usda.gov.
The best way to prevent or reduce weed encroachment is to maintain a healthy lawn through regular mowing and proper fertilization and soil pH management. Properly maintaining a lawn through these cultural practices promotes dense and vigorous turfgrass and allows the lawn to better compete with weeds. Aeration to relieve compaction and proper irrigation to manage soil moisture can increase the competitiveness of turfgrass to dallisgrass. Below are the recommended mowing heights and nitrogen fertility rates recommended for each turfgrass species. In addition to these lawn care practices, manual removal of weeds may also be necessary.
In addition to cultural practices, herbicide applications may be required to achieve effective weed control. Existing populations of dallisgrass are difficult to manage using selective herbicides. A herbicide with thiencarbazone, foramsulfuron and halosulfuron suppresses dallisgrass in bermudagrass and zoysia. When using any herbicide, you must follow the manufacturer's labeled directions.
Individual clumps of dallisgrass may be spot treated with a non-selective herbicide, such as glyphosate. For St. Augustine grass and other turfgrass species with severe dallisgrass infestations, glyphosate should be applied to kill all vegetation, followed by site preparation and new sod installation at least two weeks after the glyphosate application.
For more information regarding pesticides for turfgrass please reference the Louisiana Suggested Chemical Weed Control Guide.
For information regarding weed identification and control options please contact your local LSU AgCenter Extension Parish Office. To find your local LSU AgCenter Extension Parish Office visit here.