Six Rivers CISMA Dirty Dozen Invasive Species of the Month – Torpedograss

Six Rivers “Dirty Dozen” Invasive Species

Torpedograss (Panicum repens)

 

Define Invasive Species: must have all of the following –

• Is non-native to the area, in our case northwest Florida
• Introduced by humans, whether intentional or accidental
• Causing either an environmental or economic problem, possibly both

Define “Dirty Dozen” Species:

These are species that are well established within the CISMA and are considered, by members of the CISMA, to be one of the top 12 worst problems in our area.

 

Native Range:

Africa and Asia.

 

Introduction:

Torpedograss was initially introduced prior to 1876 in seed for forage.  In the early 1900s the USDA introduced the plant as a forage crop for pastures.

 

EDDMapS currently list 13,900 records of this plant.  They range throughout the coastal states of the southeastern U.S. but most (96%) are in Florida and those records spread across the entire state from Pensacola to the Florida Keys.

Within our CISMA there are 2262 records, most are in Okaloosa County.  The extent is probably underreported.

 

Description:

It is a tall grass reaching a height of 3-4 feet and grows along the shorelines, though it has on occasion been found more inland.  The leaves are thin, stiff, flat, and “hairy” on the top and around the sheath. It has a waxy coating that appears “whiteish” and the leaves may fold.  It has an extensive rhizome system that can grow deep into the ground and ends in a sharp point, where it gets its common name “torpedograss”.  The flowers are a panicle-type inflorescence extending from the top of the plant.

 

Issues and Impacts:

This is an aggressively growing plant dispersing primarily from fragmentation and expansion of the sharp-pointed rhizome system.  It quickly forms dense mats and out competes native grasses, many times forming monocultures along the shoreline where native plants have been removed.  By 1992 it was reported in 70% of Florida’s public waterways, restricting waterflow, recreational use, and has become particularly problematic on golf courses.

 

Management:

Torpedograss spreads primarily by extended their rhizomes, or fragments of these rhizomes.  When removing from the shoreline it is important to remove ALL of the rhizomes or the plant will return.  It is also important not to spread fragments of these rhizomes while mowing or weed-eating the plant.

It is most aggressive in open disturbed areas.  After mowing or burning land is when dense patches emerge.  Maintaining a diversity of native shoreline grasses will help impede dispersal and growth.

Mowing and disking have not been very effective.  In fact, disking may cut and spread the rhizomes.

 

When choosing chemical treatment, glyphosate has been every effective.  However, this chemical is non-selective and overspray can kill native plants you wish to keep.  Also, the plant is often in the water and an aquatic version of glyphosate should be used.  When using near water read all instructions carefully to avoid killing other aquatic plants.  Since the rhizomes can grow deep, and are at times submerged, re-treatment may be needed.

 

There are no biological agents currently approved for torpedograss management but cattle and goats both will eat the plant.  Though it does not always remove the rhizomes, grazing can be a method of control.

 

For more information on this Dirty Dozen species, contact your local extension office.

 

References

Torpedograss, University of Florida IFAS Center for Aquatic and Invasive Plants

https://plants.ifas.ufl.edu/plant-directory/panicum-repens/.

 

Early Detection and Distribution Mapping System (EDDMapS)

https://www.eddmaps.org/

 

Six Rivers CISMA

https://www.floridainvasives.org/sixrivers/