Sericea Lespedeza - The 'Dr. Jekyll and Mr. Hyde' of Plants?
Sericea lespedeza is a native of eastern Asia and can trace its roots in the United States back to 1896, when it was first planted by the North Carolina Agricultural Experiment Station. It can be easily confused with slender lespedeza, a beneficial native, as indicated in figures 1 and 2.
Sericea will form large, dense colonies across a wide range of soil types, while slender will typically occur as individual plants or as small, scattered populations. The leaflets of slender lespedeza also are narrower and more oblong than that of sericea, and slender tends to start blooming in May, whereas sericea typically will not begin blooming until July.
In 1924, the United States Department of Agriculture began work with sericea at Arlington, Va., where it was believed to be beneficial for erosion control, hay production and wildlife cover and food. In the late 1940s, it was planted extensively into pastures in the southeast. From the 1950s through the 1970s, it was used in Soil Bank plantings, bank stabilization of state and federal reservoirs and roadsides, and wildlife plantings. From these well-meaning intentions, sericea has become an invasive bully of a plant that is now found in 28 states and the District of Columbia. It has been declared a noxious weed in several counties in Kansas and Colorado.
It has turned into such a bully because of its "Dr. Jekyll and Mr. Hyde" characteristics:
- Warm-season perennial legume
- Long-lived, very persistent
- Good hay yields (5,500-6,500 pounds/acre)
- Does not cause bloat
- Tolerant of drought, acidic soils, shallow soils, low fertility
- Deep, extensive root system
- Few pests
- Well adapted
- Can have a high tannin content
- Shades competition
- Water hog
- Produces allelopathic chemicals
- High seed producer (1,000 per plant)
- High percent hard seed (easily reseeds itself)
- Seed can survive 20 years or longer
- Low nitrogen fixation
Once sericea gets started, it becomes an aggressive invader, establishing dense monocultures that are difficult to control. Oddly enough for such a vigorous plant at maturity, its seedlings are very weak, and it can be slow to establish.
So, how do we control it? Our first means of control is simple don't let it get started. Sounds too easy, but sericea invasion can be an indicator of change occurring on the range or in the pasture. Because of its weak seedlings, it needs a chance to establish. This often means that space has been created in the pasture canopy, allowing it a chance to get started. Because of the dry weather we have experienced over the last year, sericea could be on the increase this year due to space created by desirable plants dying in the dry weather.
Second, if you identify only a few plants, dig them up and get rid of them. This sounds pretty simple, too, and maybe not all that practical. But, maybe if folks had clipped off those first few cedars when they initially saw them, we wouldn't be facing the cedar problem we have today.
Chemical control also is a viable option, and, if you have only small colonies or individual plants, then spot treatment can be done. In pastures where plants are widespread, broadcast application would be better suited. The three most commonly recommended chemicals for spot and broadcast application are listed in Table 1, along with rates and timing.
Note that the timing of the particular chemical is critical for effective control. Also, don't expect one treatment to eliminate a high-level infestation. Remember, hard seed can survive for as long as 20 years, so the problem will need to be controlled for several years to come.
Other methods of control or suppression involve fire, grazing and mowing but none of these methods as a stand-alone treatment are very effective.
Burning in the spring will eliminate dead material from the previous year's growth and increase germination of new plants. However, if a chemical treatment is applied the same year as the burn, chemical efficacy can be increased because of the burn's removal of the old growth.
Mowing can reduce the vigor of a sericea stand, but, in order to do this, plants need to be mowed every time they reach a height of 12 to 18 inches. Mowing late in the season when plants are trying to build carbohydrate reserves for spring growth is the most damaging to the plant. Mowing late in the season, followed by a chemical control application the following growing season, can be effective.
Using grazing pressure to push the competitive edge from sericea back to the grass is tough. As the grazing season wears on and tannin levels rise in the sericea, grazing animals will prefer grass, allowing the sericea to flourish. Goats have been used effectively, but stocking rates need to be high enough to keep the sericea grazed below a 3- to 4-inch height. If not, then you have to be concerned with possible spread of seed through the grazing animal. Again, early intense grazing pressure followed by chemical control can be effective.
To summarize, the best management for sericea control is to not let it get started. If it does get started, identify the problem early and treat accordingly. If you are in a situation where it has established large colonies, then a combination of treatment methods may be the most effective. Also, don't expect the problem to go away in a year after chemical treatment, you may be mopping up for a few years to come.