The devil’s own weed is how some are describing sericea lespedeza (Lespedeza cuneata). Cattle won't eat it, herbicides only slow it, and proper range management seems to help it thrive. With few natural enemies and prolific seed production (up to 1,500 seeds per plant), the perennial legume first introduced to the United States as a cover crop on reservoirs and reclaimed strip mines is rapidly invading the prairie. Once established, sericea (pronounced se-re'se-e) lespedeza crowds out native prairie grasses and range scientists warn it threatens the tallgrass prairie and the livelihood of many ranchers and rural communities.
“Most frightening,” says Emporia State University biologist Thomas Eddy, “is that sericea lespedeza is the only plant we are aware of to invade the prairie and crowd out the native prairie grasses.”
By far the most severe damage by sericea lespedeza is in the Flint Hills of eastern Kansas. But researchers say problems exist in other areas, including Oklahoma, Missouri, Nebraska and western Kansas. Left unchecked, sericea lespedeza could present a threat to all untilled regions of the Great Plains.
“Sericea lespedeza is more abundant in areas with 30 inches or more rainfall per year,” says Kansas State University agronomist Walt Fick. “But we’re finding problems in western Kansas and other parts of the High Plains where rainfall is 18 to 20 inches.”
Ranchers must understand the distinction between the desirable species of lespedeza, such as Korean and common lespedeza, and sericea lespedeza, says Dr. Fink. “Annual lespedezas are desirable forages that do not present the problems associated with sericea.”
From forage to weed
Sericea lespedeza, also known as Chinese bush clover, was first introduced into North Carolina in 1896 for erosion control and as a forage crop. In the 1930s it was planted on strip mines in southeast Kansas and in the 1940s and 1950s was planted around state and federal reservoirs.
In the southeastern United States, sericea lespedeza is used as a hay and forage crop. When grazed or hayed in its early states, sericea lespedeza is a palatable forage high in protein. But sericea lespedeza also has high concentrations of chemical compounds called tannins. Tannins bind with proteins leaving them unavailable for digestion. The tannins found in sericea lespedeza reduce the plant’s palatability as the level of tannins increase with the maturity of the plant. Ranchers and scientists say the tannins are why cattle will graze sericea lespedeza sparingly in its early stages, and avoid the plants altogether later in the season. However, researchers say livestock readily consume sericea lespedeza hay since field drying decreases the tannin concentration.
Sericea lespedeza was first recognized as a potential weed problem in southeast Kansas in the early 1980s. By 1998 at least 53 counties in Kansas reported the occurrence of sericea lespedeza with more than 300,000 acres infested.
As the extension agent for Kansas State University in Greenwood County, Jeff Davidson lives at ground zero of the sericea invasion.
"We have pastures that are totally lost to sericea lespedeza, and others that will be lost if control measures are not implemented," Mr. Davidson says. "But control of sericea lespedeza is difficult and expensive."
Two herbicides are known to be effective on sericea lespedeza. Remedy, manufactured by Dow Agro Sciences, and Escort, manufactured by DuPont, are recommended for controlling sericea lespedeza. But area ranchers consider both products expensive.
"Pastures in this county rent for $15 or $16 per acre," Mr. Davidson says. "An aerial application of either Remedy or Escort will cost $15 to $20 per acre. So it costs more than one year's income from the land to kill the sericea."
And spraying does not eliminate the problem. The seeds of sericea lespedeza may germinate up to 10 years or more after they are produced. "We may need to spray one year out of three just to keep it under control," Mr. Davidson says.
Spraying also has undesirable side effects, says Emporia State's Dr. Eddy. "When we use a herbicide that kills sericea lespedeza, we also kill other desirable broadleaf prairie plants, such as lead plant and wild alfalfa."
Preliminary research suggests a more economical control of sericea lespedeza can be obtained by grazing goats in infested pastures. An experiment by the Kansas Department of Wildlife and Parks, in cooperation with Emporia State and Oklahoma's Langston University, has shown that goats can greatly reduce the seed production and height of sericea lespedeza. And several ranchers in the Flint Hills already are developing goat herds to work in unison with cattle grazing.
"Goats will graze the sericea lespedeza and other weeds rather than the grass," explains Mr. Davidson. "Therefore, ranchers can run goats with their cattle without fear of overgrazing. They won't eliminate the sericea, but the objective is to prevent the sericea from maturing and producing seeds."
Researchers concede that goats are not the total answer. "We have 5.5 million acres of Flint Hills," says Dr. Eddy. "There simply aren't enough goats to deal with our problem. And I'm not sure we can develop a goat culture in this region."
Other than goats, the only natural enemy to sericea lespedeza researchers have found is the lespedeza webworm (see sidebar). For the past year Dr. Eddy has studied the webworm and has found some encouraging results. The Webworm envelops two or three stems of sericea lespedeza in silk, feeding on the leaves. Where encased in silk, photosynthesis stops and the plant fails to flower and seed.
"We hope to be able to transport the Webworms to locations that don't have them now," Dr. Eddy says. "We hope the worms will help us slow, down the spread of sericea lespedeza.”
But like herbicides and goat grazing, the lespedeza webworm is not viewed as a silver bullet.
At this point researchers are seeking to control, rather than eliminate, sericea lespedeza.
"We must learn to live with it," says Mr. Davidson, "Our best strategy is prevention. Ranchers must learn to identify sericea lespedeza and to act quickly when they find an invasion. At a minimum, we want to prevent seed production through mowing or grazing, if possible."
For more information about sericea lespedeza: www.oznet.ksu.edu
Controlling sericea lespedeza
The invasion of rangeland by sericea lespedeza presents a unique challenge to range scientists and land stewards. Traditional management techniques do little to prevent or control sericea lespedeza, but here's what authorities recommend:
- Don't overgraze. Use proper management to keep native grasses and pastures as healthy as possible.
- Early detection. Learn to identify sericea lespedeza and start control measures early.
- Prevent seed production. Mow or spray small, early-detected areas. Flowering occurs in late August and September with seed production following.
- Spray large infestations. Spraying is a quick, effective control, but infestations will return from seeds in the following one to three years. Spraying may be required one year in three, or more often, to provide desired control.
- Use alternative controls. Goats will graze sericea lespedeza and prevent seed production. Lespedeza webworms (photos at left) can defoliate individual plants.
- Avoid burning severely infested areas unless you plan to follow with grazing or herbicides. Range burning, an effective grassland management tool, also assists sericea lespedeza.
- Promote awareness. Make sure your neighbors recognize infestations of sericea lespedeza, and understand the danger the weed represents if uncontrolled.