Torpedo Grass (Panicum repens) is a warm-season perennial grass native to Africa and Eurasia but now widespread across warm climates, particularly the US South. This invasive species was originally introduced for use as a forage crop but quickly became a major problem in turf, landscapes, and aquatic environments. Effective management requires a multi-year strategy combining accurate identification, non-chemical control for small areas, and repeated systemic herbicide applications for widespread infestations.
Identifying Torpedo Grass and Its Growth Habit
Torpedo Grass can reach heights of up to 40 inches if left unmowed, though it often blends into turfgrass when regularly cut. The leaves are stiff, linear, and may have a waxy or whitish coating, often with fine hairs present on the leaf sheaths. Its most defining feature, which gives the plant its name, is its underground growth structure.
The plant produces robust, sharp-tipped underground stems known as rhizomes. These rhizomes act as energy storage units and can penetrate compacted soil, landscape fabric, and even thin plastic sheeting. They can travel a foot or more deep and spread horizontally for several feet. This extensive, deeply buried network is the primary reason the weed is difficult to eradicate, as any small fragment left behind can regenerate into a new plant.
Non-Chemical Eradication Methods
For small, isolated patches or areas where chemical use is restricted, physical and cultural controls can be effective. Manual removal is often counterproductive because the rhizomes easily break, leaving small pieces in the soil that quickly sprout new growth. It is only a viable option for new, small invasions where the entire root mass can be meticulously dug out and removed.
Smothering uses thick, opaque layers to deprive the weed of sunlight and air. This method involves laying down materials like heavy, overlapping cardboard or dark, impermeable plastic over the infested area. The covering should then be topped with 4 to 6 inches of mulch. This process works slowly by starving the plant of light, and it may need to remain in place for an entire growing season to fully exhaust the rhizome network.
Solarization uses the sun’s heat to kill the plant and its rhizomes. To prepare for solarization, the grass should be mowed as short as possible, and the soil should be thoroughly watered to improve heat conduction. The area is then covered with clear, heavy-duty plastic sheeting, typically 4 to 6 mil thick, with the edges buried to trap the heat. The intense solar heat, ideally exceeding 103 degrees Fahrenheit in the soil, must be maintained for six to eight weeks during the hottest part of the summer.
Systemic Herbicide Application
Chemical control is often the most reliable method for large or well-established Torpedo Grass infestations. The use of systemic herbicides is important because they are absorbed by the leaves and then transported, or translocated, down to the deep rhizomes. Multiple applications are required to exhaust the energy stores within the underground runners.
For areas without desirable plants, a non-selective systemic herbicide containing glyphosate is highly effective. A 2% to 3% glyphosate solution applied to the foliage will travel through the plant to the rhizomes. Because the herbicide must move throughout the extensive root system, it is important to allow a minimum of two to five days after application before mowing the treated area.
In established turfgrass, selective herbicides must be chosen based on the type of grass being protected. Lawns with Zoysiagrass or Bermudagrass can tolerate sequential applications of quinclorac. Applications should be spaced approximately three to four weeks apart during the active growing season. To increase the herbicide’s effectiveness, a specialized additive like methylated seed oil (MSO) is often recommended to help the chemical penetrate the plant’s waxy leaf surface.
Managing Torpedo Grass in Centipedegrass and Bahiagrass is difficult due to fewer selective options. Herbicides containing sethoxydim can provide suppression of the weed in these turf types. However, this ingredient does not offer complete eradication and requires repeated treatments throughout the summer to keep the weed in check. The ideal time for any herbicide application is when the grass is actively growing and healthy, typically in the late spring or early summer.
Post-Treatment Monitoring and Lawn Recovery
After the initial eradication treatment, the process shifts to monitoring and turf re-establishment. Once the treated grass has died back, the area should be cleared of debris to prepare for new planting. Tilling the soil should be avoided, as this can bring dormant seeds to the surface and fragment any surviving rhizomes, triggering new growth.
The treated area must be watched closely for any signs of regrowth, which can appear weeks or months after the initial treatment. Any new shoots must be spot-treated immediately with the appropriate herbicide to prevent the rhizome from rebuilding its energy reserves. This vigilance often requires attention for a full year or more.
Re-establishing a dense, healthy lawn acts as a long-term preventative measure against future invasions. A vigorous turfgrass variety will naturally outcompete new weed sprouts by shading the soil. Cultivating the lawn with deep, infrequent irrigation is advisable, as Torpedo Grass thrives in saturated or poorly drained soil conditions. Maintaining a proper mowing height and a consistent fertilization schedule will encourage the desired turf to form a dense canopy, making the environment unfavorable for its return.