Sericea Lespedeza: Eliminate Small Infestations Now or Deal With Bigger Problems Later By Kevin Bradley

In spite of the dry weather we are experiencing throughout most of the state, one species that you may have noticed remaining distinctly green among our drought-stricken pastures and hay fields is sericea lespedeza (Lespedeza cuneata). Why is this? Well ironically enough, sericea lespedeza just happens to be a plant that is extremely drought hardy. And this is just one of the characteristics of sericea lespedeza that make it a competitive, invasive species that you don’t want on your property.

In case you aren’t familiar with sericea lespedeza, it is a non-native perennial legume that was introduced into the United States in 1896 as a forage crop. It resembles many other annual lespedezas utilized for forage but has erect stems that may reach as much as 5 feet in height (Figure 1). Sericea has trifoliate leaves with conspicuous points at the leaf tips. Individual leaves are rarely longer than 1 inch in length and have hairs on the leaf undersides only. Sericea plants are usually highly branched in the upper canopy and plants can occur as a single stem or as several stems that originate from the same perennial base.

Figure 1

In the early 1930’s, sericea was often planted in Kansas and Missouri for erosion control, wildlife habitat, and occasionally for use as a forage. Over the last several decades, however, sericea has developed into a significant problem weed of pastures, hay fields, and roadside rights-of-way. It can tolerate a variety of soil conditions and competes with native vegetation for moisture, nutrients, and sunlight. It has the ability to emit chemicals that inhibit the germination and development of nearby plants (called allelopathy), and it is also a prolific seed producer (Figure 2). In 1970, some researchers found that established sericea plants could produce as much as 600 pounds of seed per acre annually.

Sericea can become a damaging invader in pastures, hay fields, and partially wooded sites. In these areas, grazing by cattle is limited to young, tender growth because these plants become unpalatable as the plants mature. For example, some research conducted in the early 1940’s revealed that tannin levels increased from 6 to 21 percent as sericea increased from 4 to 36 inches in height. Because of this, cattle tend to selectively graze around the stiff stems during the latter part of the summer resulting in the production of additional seed for the following year.

Because of its highly competitive nature, sericea lespedeza was declared a statewide noxious weed in Kansas in 2000. Sericea appears to be spreading northward into Nebraska and eastward throughout Missouri. It is not currently declared a noxious weed in Missouri, although it now occurs in most of the counties in this state.

In most areas of Missouri, sericea will soon be approaching the bloom stage of growth. Sericea’s flowers are not as noticeable as many other species but upon closer examination of these plants you will find white to yellow flowers with purple tinges located in the upper leaf axils of the stems.

Figure 2

This stage is important because several studies have shown that the herbicide metsulfuron is particularly effective on sericea when applied during the bloom stage of growth. Metsulfuron is the active ingredient in Cimarron (which used to be sold as Ally) and Escort, and is also included with 2, 4-D and dicamba in a prepackaged herbicide mix sold as Cimarron Max. Either of these products should provide good control of sericea when applied in the bloom stage of growth.

Another option is to apply triclopyr or herbicides that contain triclopyr when sericea is in the vegetative stage of growth and usually no taller than knee-high in height. In our research studies, this has corresponded to a late-May to mid-June timeframe. Triclopyr is the active ingredient in Remedy and is also one of the components of Crossbow and PastureGard. PastureGard is a new herbicide that just became available for use in Missouri this season, and our evaluations of this herbicide on sericea have been promising. Although we have only collected one year of data thus far, our initial results indicate that we achieved greater than 95% control of sericea lespedeza when we applied 2 pints of PastureGard per acre in mid-June. Similar or higher levels of control were achieved with Remedy applications made during the same timeframe.

One non-chemical option for controlling sericea lespedeza is to graze heavily infested areas with goats, which will eat the sericea regardless of tannin content. Stocking rates must be adjusted to levels that will keep the sericea below a 3 or 4 inch height. This method should prevent seed production and may eliminate sericea lespedeza infestations altogether after several years. Another way to reduce seed production is to mow plants consecutively throughout the growing season, which will deplete the perennial rootstocks significantly but it is unlikely that mowing alone will eliminate sericea lespedeza infestations.

If you’ve had sericea lespedeza on your property for several years, you certainly can get good control of existing infestations with the herbicidal options discussed above (metsulfuron in the bloom stage and triclopyr in the vegetative stage). However, it’s still unlikely that you will be able to "close the book" on the sericea lespedeza chapter forever. Why? Because unfortunately another characteristic of sericea is its ability to produce seed that can remain viable in the soil for as many as 20 years. With plants that are able to produce several thousand seed each, you can see that new sericea seedlings may be a problem for years to come. In other words, eradicating existing stands that have been established for several years is rarely a one time event. This is why early detection and elimination of small sericea infestations now will save you lots of money in the longrun.

Kevin Bradley, Weed Science
573-882-4039