Torpedograss a Challenge to Manage on Land or Water

Tordpedograss (Panicum reopens) is one of the most concerning weeds in Florida and now easily found in the Panhandle. This weed’s favorite habitat is in or near ponds and ditches, but will spread across lawns and pastures.

A native grass of both Africa and Asia, torpedograss was introduced through seed in the U.S in the late 1800’s as a forage crop for livestock. Torpedograss is in the family Poaceae, along with other grasses such as the persistent invasive threat, cogongrass, as well as common bermudagrass. It gets its name from the sharply pointed tip and not only is it exceptionally fast spreading, it can grow as tall as 3 feet. Torpedograss is a poor seed germinating species in our climate and primarily relies on rhizome expansion.

Photo: Tordpedograss (Panicum reopens).

Credit: Ray Bodrey, UF/IFAS Extension Gulf County.

This plant has a tendency to choke out and completely take over native vegetation. Agronomist in south Florida have been concerned about it for years. In 1950, the University of Florida agricultural experimental station warned: “Torpedograss is a serious weed when established in farm or grove land and indiscriminate planting without the regard to future crops or adjoining land is dangerous.” (Hodges and Jones).

Photo: Tordpedograss pond infestation.

Credit: Jeff Hutchinson, UF.

So, what is the impact of torpedograss on Florida?

Since 1992, torpedograss has taken over 70% of Florida’s public waterways. Lake Okeechobee is considered ground zero with approximately 7,000 acres of native marsh now displaced. These dense mats of grass can impede water flow in stormwater applications, and restrict usage of irrigation holding ponds and fish ponds.

How does one manage this invasive grass?

Infestation prevention can be accomplished by controlling the rhizome expansion. This is easier said than done, as a small rhizome fragment left behind will no doubt cause re-establishment. Keeping the infestation at bay, by controlling the spread at waterways is key.

For IPM (integrated pest management) solutions follow these steps:

For cultural management, invasive plants tend to quickly establish in open or recently tilled areas. So, prescribed burn and clearing by mowing are methods that tend to promote infestations. A healthy, diverse landscape with native plants, or species with non-invasive tendencies will provide a level of defense.

Mechanical control is not very effective. Tilling the land only spreads the rhizomes through fragmentation.

There are few biological controls, although cattle and goats will graze and they may continue to spread the grass.

Chemical control using Glyphosate (Roundup, etc.) at a 2-3% solution and imazapyr (Arsenal, Chopper or Habitat) at 0.5 to 1 % solution has been effective for on land use. Aquatic herbicides with glyphosate (Rodeo, etc.) are effective for ponds. This can be applied in a liquid or granular form. A non-ionic surfactant will be needed to adhere the liquid chemical with success. Keep in mind, these herbicides are systemic, meaning they are absorbed and move through out the plant tissue. Be sure to minimize over spray damage of desirable plants, especially related to drift. Imazapyr also has longer soil activity and could impact sensitive oaks. Torpedograss is much more difficult to treat in water and will require multiple applications to completely control whether in water or on land.

For more information on torpedograss, contact your local county extension office.

Information for this article provided by the UF/IFAS Center for Aquatic and Invasive Plants:  https://plants.ifas.ufl.edu/plant-directory/panicum-repens/ and the Wetlands Weeds Journal article “Torpedograss – Forage Gone Wild” by Ken Langeland & Brian Smith of UF/IFAS and Charles Hanlon of the South Florida Water Management District: https://www.se-eppc.org/wildlandweeds/pdf/su98-langeland-p4-6.pdf

UF/IFAS Extension is an Equal Opportunity Institution.