Managing Two Highly Invasive Weed Species in Landscapes

Weeds that invade landscapes often can pose serious problems. Some of the toughest weeds to manage are those that spread vegetatively through rhizomes or some other underground storage organ. Regular treatments with herbicides are the surest way to conquer two of these weeds, bushkiller and torpedograss.

Cayratia japonica (Bushkiller)

Bushkiller vine is a highly invasive summer perennial that infests home landscapes across the Gulf Coast. Native to Asia, bushkiller gets its name because the vine rapidly climbs over desirable landscape plants and kills them by blocking out sunlight. The vine has compound leaves with five leaflets that are ovate to orbicular, 3 or more inches long and 0.5 to 1.5 inches wide. Often bushkiller is confused with another five leaflet vine, Virginia creeper (Parthenocissus quinquefolia). However, the middle leaflet on bushkiller has its own stem. Bushkiller has tendrils that grow opposite each leaf and salmon-colored flowers that produce berries that contain two to four seeds. The vine mainly reproduces vegetatively as the seeds do not have high viability.

Bushkiller vine control: Once bushkiller vine invades landscapes, hand removal is difficult. All of the roots must be removed because of the vine’s ability to re-sprout from roots and rhizome material left in the soil. Research conducted at the LSU AgCenter has shown that repeated applications of the herbicides triclopyr or glyphosate can be effective. However, the vine engulfs flower beds and becomes entangled in desirable vegetation, making spraying difficult. In areas where spraying is not possible, pulling vines away from landscape plants and wiping or brushing the leaves and stems with a 10% solution glyphosate (using 41% glyphosate active ingredient formulation) in water can be effective.

Mix sizeFluid ounces of 41% glyphosate concentration to add to water
1 gallon of water13
1 quart of water3

Panicum repens (Torpedograss)Regardless of the method used, removing bushkiller vine from the landscape will likely take years of persistent herbicide treatment.

Torpedograss is a perennial rhizomatous grass that is considered one of the most invasive grasses in the world. The grass is characterized by creeping, pointed, torpedo-shaped rhizomes. Torpedograss has erect leaves that may be up to 10 inches long and 0.3 inches wide. The inner side of the leaf sheath is membranous with short hairs. Although the plant produces seeds, they are not viable. The weedy grass solely reproduces vegetatively by robust rhizomes.

The spread of torpedograss in Louisiana is mainly attributed to the movement of soils infested with weed from the Bonnet Carré Spillway. The spillway is located just west of New Orleans and is the main source of plant material for southeast Louisiana, especially within the New Orleans metro area. The weed will grow in a wide range of soil types and is salt tolerant.

Torpedograss is often introduced into new areas during construction by using soil contaminated with rhizomes. Once introduced into landscapes, torpedograss quickly becomes the predominant species in flower beds and home lawns. There are currently no effective control options in centipedegrass or St. Augustinegrass lawns. The herbicide quinclorac reduces torpedograss infestations in bermudagrass and zoysiagrass lawns.

Hand removal is not an effective option for eliminating torpedograss in landscape beds. Selective grass-killing herbicides such as sethoxydim and fluazifop only temporarily suppress the weed’s growth, although fluazifop is more effective than sethoxydim. In landscape beds, carefully wiping or brushing the torpedograss leaves and stems with a 10% solution of glyphosate (using 41% glyphosate active ingredient formulation) in water can be effective with repeated use over several growing seasons.

Ron Strahan is an extension weed scientist.

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Bushkiller vine engulfs landscape plants blocking out sunlight. Photo by Ron Strahan

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Bushkiller leaf. Photo by Ron Strahan

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Torpedograss outcompetes centipedegrass. Photo by Ron Strahan

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Virginia creeper can often be confused with bushkiller.Photo by Ron Strahan

4/9/2017 6:09:18 PM
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