Taking on the challenges of torpedo grass

Torpedo grass is a weedy invader you do not want mixing in with your turf grass.

Even some of the most ardent eco-concerned gardeners are willing to use a chemical herbicide to suppress it.

Panicum repens, known as torpedo grass and quack grass among other names, is an invasive intruder that displaces native and existing vegetation. It is a bane in coastal lawns and gardens.

The grass spreads primarily by rhizomes. It does produce seeds, but they are not known to be viable in the US. The grass’s hard sharp rhizomes travel horizontally underground—not on or near the surface like centipede. Underground growth is typically creamy white and waxy-looking. The rhizomes are hard to track and remove because they can run vertically 12 or more inches below ground. Their torpedo-like points easily penetrate landscape fabric; and they readily grow under landscape curbing and barriers.

Torpedo grass is a fast growing warm season perennial grass that can tolerate drying and flooding. Above ground it is sometimes confused with Bermuda grass. The leaf blades are narrow, stiff and straight, flat or folded. They arise from auxiliary buds that develop along length of the rhizome. The grass grows to form dense monocultures replacing native or existing vegetation.

Panicum repens was introduced to the southeast in late 1800s as cattle forage grass, but likely arrived prior to that in ballast water from ships. In the early 1900s the USDA imported torpedo grass seed to plant as forage grass for cattle. It has long since lost favor to more nutritious grasses.

Like other invasive exotic imports torpedo grass has escaped the areas where it was once grown and become an invasive problem. It is thought to have originated in Eurasia and Africa. Today it is found in tropical and subtropical areas around the world. In the US it grows in the coastal states from Texas to North Carolina and in California and Hawaii.

The grass does not tolerate cold weather and dies back with frost, but its deep rhizomes easily overwinter.

Moderately salt tolerant torpedo grass grows in a variety of wet environments from marsh to off shore in water up to six feet deep where it forms dense floating mats. Although torpedo grass is often associated with moist sandy soils, it also grows in heavy upland soils. Once established it is difficult to kill. It does not have any known pests or problems.

There is no easy way to control torpedo grass; none of today’s chemicals can eliminate it. Consequently, homeowners need to routinely watch for it and, when identified, promptly start treatment to suppress it.

Torpedo grass spreads by rhizomes. Hand pulling is not recommended as a method of control because it leaves bits and pieces of the roots and stems behind to grow.

In gardens apply glyphosate at the highest label rate to the leaf blades. Always read and follow label instructions on the herbicide container. Glyphosate (Round Up and such) is nonselective; therefore, it critical to protect other plant foliage from its direct spray and drift. Glyphosate is safe to use in garden areas as long as you do not get the chemical on ornamentals. Repeat applications will be necessary to maintain suppression.

To control torpedo grass in lawns use a selective herbicide appropriate for your type of grass. Again, repeat applications are necessary to maintain suppression.

On centipede lawns sethoxydim (Vantage) suppresses torpedo grass without harming turf. Use it according to label directions.

On Bermuda and zoysia lawns quinclorac (Image for homeowners or Drive for commercial applicators) suppresses torpedo grass. Read and follow label directions.

Avoid any herbicide that contains imazapyr because the chemical stays in the soil. The residual effect on soil can harm trees and shrubs.

There is no selective weed killer available for use on St. Augustine grass.

If a manageably small section of lawn has been colonized by torpedo grass the options are clearing the grass by solarization or with glyphosate and then replanting your choice of grass. If torpedo grass invasion is widespread total lawn renovation will be necessary to restore turfgrass.

This story was originally published May 24, 2017 at 5:00 AM with the headline "Taking on the challenges of torpedo grass."