Matthew Foster, Albert Orgeron and Kenneth Gravois

Torpedograss (Panicum repens) is no stranger to south Louisiana, where it is commonly found in wetland areas, landscapes and along roadsides. Recent documentation of its presence in St. John the Baptist Parish sugarcane fields, however, prompted new LSU AgCenter research trials to develop management recommendations.

This perennial, rhizomatous grass is a major weed problem in many tropical and subtropical regions of the world. The first reported sighting in the United States was near Mobile, Alabama, in 1876. In the early 1900s, the U.S. Department of Agriculture tried incorporating torpedograss into forage systems, but it proved inferior as a forage crop. Additionally, it is found in the Carolinas, Georgia, Florida, Mississippi, Texas, California and Hawaii. It is considered one of the most invasive weeds in the world. The Louisiana Department of Wildlife and Fisheries classifies torpedograss as a Tier I invasive species, which is defined as “species currently causing severe or widespread negative impacts on wildlife or natural communities.”

Its spread throughout south Louisiana is mainly attributed to the transfer and use of rhizome-infested soils from the Bonnet Carré Spillway. In St. John the Baptist Parish, the weed has most likely been present in these sugarcane fields for several years and mistaken for bermudagrass (Cynodon dactylon). Torpedograss is a weed pest of sugarcane in Florida, Taiwan and Japan. Previous research in Japan reported that severe torpedograss infestations can reduce sugarcane yield by as much as 80%.

Torpedograss is characterized by long, creeping rhizomes with a sharp, pointed end that resembles a torpedo. The plant allocates much of its biomass to the rhizomes, which are strong enough to penetrate wood and asphalt and can run deep underground. Up to 80% of torpedograss biomass occurs underground as rhizomes and roots. The rhizomes can regenerate and produce new roots and shoots at every node, creating large, dense stands even from small pieces. It has erect, waxy, silver-green leaves that are pointed at the tip and can be up to 0.3 inches wide and 10 inches long. Leaves can be flat or folded, and hair is typically present on the surface and around the sheath. Seed heads are small and flat and are white to brown in color. Plants often produce seed, but they are not viable. Propagation only occurs vegetatively by rhizome growth. In wetland areas, rhizomes may float or move with soil after flooding events. Optimal growth occurs when day and night temperatures exceed 77 F. When fully mature, torpedograss can grow up to 3 feet tall and form dense mats that displace native vegetation.

Management of torpedograss is extremely difficult due to an aggressive growth habit, perennial life cycle, ability to survive in adverse environmental conditions and tolerance of herbicides. Because torpedograss spreads by rhizomes, preemergence herbicides are not an effective control option. Sugarcane weed management programs in Louisiana rely heavily on preemergence herbicides; however, products such as asulam and trifloxysulfuron (Envoke) are commonly utilized for postemergence control of johnsongrass (Sorghum halepense), itchgrass (Rottboellia cochinchinensis), vaseygrass (Paspalum urvillei) and several other annual grasses. Research conducted in sugarcane in Japan reported that three sequential asulam applications at 3.2 quarts per acre at 40-day intervals reduced torpedograss regrowth for nearly one year. In bermudagrass turf research in Florida, sequential applications of trifloxysulfuron (labeled as Monument in turf) at 0.5 ounces per acre resulted in 87% torpedograss control.

To develop torpedograss management recommendations for the Louisiana sugarcane industry, the AgCenter conducted two research trials during 2024 and 2025. In August 2024, a fallow field in Paulina was utilized to evaluate herbicide efficacy on torpedograss. Herbicide treatments included: (1) asulam at 4 quarts per acre, (2) asulam at 2 quarts per acre plus Envoke at 0.3 ounces per acre and (3) asulam at 4 quarts per acre plus triclopyr (Trycera) at 1.4 quarts per acre. Crop oil concentrate at 1% volume per volume percentage was added to all treatments, and a nontreated control was included for comparison. Weed control was assessed using a visual rating of 0 (no effect) to 100% (complete plant death). At 36 days after treatment, torpedograss control was 80% for all herbicide treatments.

In July 2025, a replicated trial utilizing the previously mentioned treatments and rating method was conducted in a commercial sugarcane field in LaPlace. Treatments were applied postemergence-directed to a field of third stubble cane or the fourth crop after initial planting. At 35 days after treatment, torpedograss control was 90% for asulam applied alone or in combination with Envoke; however, control increased to 98% when Trycera was applied with asulam. At 69 days after treatment, aboveground shoot biomass was collected from a 144-square-foot area in each plot. Dry weights of each sample were measured, and data were converted to a percent reduction from the nontreated control. All treatments reduced torpedograss dry weight by 60%.

Short-term control of torpedograss in Louisiana sugarcane is possible. For long-term control, additional in-crop herbicide applications may be necessary. Like many other grassy weeds, a fallow program that integrates multiple applications of glyphosate along with tillage is the best control measure for torpedograss. Future research will evaluate additional management strategies and the impact of torpedograss on sugarcane yield.

Matthew Foster is the LSU AgCenter sugarcane weed specialist and is stationed at the AgCenter Sugar Research Station in St. Gabriel. Albert Orgeron is the coordinator of the Sugar Research Station, and Kenneth Gravois is the AgCenter state sugarcane specialist.

This article appears in the winter 2026 edition of Louisiana Agriculture magazine.

Torpedograss growing between rows of sugarcane in LaPlace, Louisiana. Photo by Kyle Peveto

Torpedograss that was not sprayed with herbicide. Photo by Kyle Peveto

Torpedograss 35 days after being sprayed with asulam at 4 quarts per acre. Photo by Kyle Peveto

Torpedograss 35 days after being sprayed with asulam at 2 quarts per acre plus Envoke at 0.3 ounces per acre. Photo by Kyle Peveto

Torpedograss 35 days after being sprayed with asulam at 4 quarts per acre plus Trycera at 1.4 quarts per acre. Photo by Kyle Peveto

Rhizome and root structures of torpedograss. Photo by Zachary Taylor