“What is the deal with torpedo grass? It is taking over my neighborhood and we are desperate to know how to control it,” asks Ron Glancy. A resident of the West Bank of Greater New Orleans, Ron finds lots of invasive life and shares his discoveries.
Well, there are no happy solutions to the torpedo grass invasion, reports Andrew Loyd, local LSU AgCenter Extension Agent. He says, "You can't control it, you can only manage it."
The species, Panicum repens, was introduced to the United States from Asia in 1920 by the U.S. Department of Agriculture. Its intended purpose was to provide a new forage crop for cattle. Cows do eat it, but it has very low nutritional value to them, and it is toxic to horses.
It does well along the Gulf coast, and is known from northern Louisiana and Mississippi, as well as Arkansas, but cool temperatures give it grief, so it can’t spread much farther north.
Although it does produce seed, in the U.S. these seeds are infertile and do not contribute to the dispersal of the species. It is unfortunate, however, that it spreads vigorously vegetatively – from parts of its root system being moved around. Once established it is akin to Attila the Hun as it marauds nature by rapidly growing stolons that run a foot or so beneath the surface in all directions. One day you don't have it in your yard, and the next it is popping up everywhere.
So how does it arrive at your abode? The most widespread way is if you buy river sand, especially originating from the Bonnet Carré spillway. Torpedo grass is abundant there. It can, however, come from other sources in and around the city. If buying soil, one should always ask if it is “torpedo grass free.” If they guarantee it, it probably is. If they equivocate, beware!
And why be so cautious? Because once you have it, it is near impossible to eliminate. Dr. Ron Strahan, torpedo grass research leader with the LSU AgCenter Extension Service, says the only option that normally works is to completely dig up your yard, down several feet, and replace the soil with uncontaminated soil - a very expensive and labor intensive endeavor, indeed. Even then, Strahan says, you run the very real risk of the species reinvading your property from a neighbor’s yard. If it is nearby, it will be back!
Dr. Strahan stated that there are no chemical controls that work on torpedo grass in our most popular lawn turf, St. Augustine. Any herbicide containing sethoxydim will suppress it temporarily, but it will probably survive. An option is to replace the St. Augustine with either zoysia grass (if shade is present) or Bermuda grass in sunny areas. If you choose this route, you will have to often treat your yard using the herbicide "Drive" (containing the active ingredient quinclorac). Drive will keep torpedo grass from dominating, but its application will be an ongoing activity.
Grant Estrade, of Laughing Buddha Nursery and Wood Materials, says the best controls include creating shady spaces. Torpedo grass doesn't do well in the shade, so it is at least somewhat suppressed. Under bushes in the sun, it will grow very tall, and extend above the leaves on the bushes, such as azaleas.
Torpedo grass seems to have no controls anywhere in our environment. It even tolerates salt, and grows on barrier islands. We don’t think that even nutria will eat it!
Our neighbors to the north may not continue to escape this challenging grass. Biologists who study the ecology of plants and animals have for years reported changes in the phenology (relationship of temperature and other environmental factors to activity) of their research subjects. They have noted that over the years, there are signs that spring weather is arriving earlier in increasingly northern latitudes – frogs are calling earlier, flowers are blooming sooner, salamanders are mating days or weeks before established norms. All these ecological signals are being interpreted as subtle adjustments due to climate change. Will torpedo grass begin to expand its range northward? Nothing is suggesting otherwise.
Sorry, Ron. Wish I could be more encouraging. Sometimes invasive species just win!