Korean Clover (Korean Lespedeza) (Invasive Exotic Plants of North Carolina)

Korean Clover (Korean Lespedeza)

Kummerowia stipulacea

Summary ⁴

Kummerowia stipulacea is a species of flowering plant in the legume family known by the common name Korean clover. It is native to China, Japan, Korea, and Russia, and it is present in the eastern United States as an introduced species.

Impacts and control ⁵

More info for the terms: fire management, forbs, invasive species, natural, prescribed fire, reclamation

Impacts: Few sources reported that Japanese and Korean clovers have negative impacts on natural vegetation. Although some aggressive growth by the clovers has been reported in prairies [101], other herbaceous communities [105], and reclaimed mine sites [19], the clovers are not usually weed management priorities. Their persistence and spread typically require recurring disturbance [73,101,144].

In some herbaceous vegetation types, the clovers have impacted associated vegetation. Soon after its introduction to the Gulf Coast states, one researcher noted prolific spread and growth of Japanese clover. Populations covered "immense" areas east of the Mississippi and were "crowding out almost completely the herbaceous indigenous plants". The researcher noted that Japanese clover established in "thickly matted stolons" of the nonnative Bermuda grass (Cynodon dactylon) [105]. In Kentucky, Illinois, and Indiana, the clovers were often used to seed surface-mine sites. Use of the clovers in mine reclamation "contributed to the creation of stable yet very floristically simple nonnative communities&quot [19]. In New York, Japanese clover occurred in seasonally mowed herbaceous vegetation bordering a pitch pine (Pinus rigida)-oak forest. Near Japanese clover populations were 5 forbs considered threatened or endangered in New York: lesser snakeroot (Ageratina aromatica var. aromatic), white colicroot (Aletris farinosa), New England blazing star (Liatris scariosa var. novae-angliae), sandplain flax (Linum intercursum), and narrowleaf whitetop aster (Sericocarpus linifolius) [82,152]. Potential or current impacts of Japanese clover on these species were not discussed in the study.

In crop-production reports, Japanese and Korean clovers are not considered especially aggressive, and established stands are easily invaded by other vegetation. Reports indicate that weeds encroach rapidly in pure stands of Japanese and Korean clover, and due to their short growing season, the clovers do not "compete well" with other "weedy" plants [8,113]. Growth of the clovers does not appear to be inhibited by nonsod-forming grasses, but the clovers can be eliminated by the second growing season when grown with sod-forming grasses such as Bermuda grass or carpetgrass (Axonopus spp.) [58].

Allelopathy: Laboratory experiments showed that root exudates from Japanese clover inhibited the growth of lettuce radicles [29]. How these findings may apply to other vegetation and field conditions is unknown.

Climate change: Controlled experiments suggest that Korean clover productivity could increase with increasing carbon dioxide levels associated with global climate change. Total Korean clover biomass was significantly (P≤0.05) greater in elevated than in ambient carbon dioxide conditions. Korean clover test plants were grown in low-phosphorus soil collected from a citrus orchard in China [141].

Control: Few studies reported on the best methods to control Japanese or Korean clover populations. General weed control theory suggests that control of biotic invasions is most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual invaders [89]. In all cases where the clovers are targeted for control, the potential for other invasive species to fill their void must be considered [18].

Fire: For information on the use of prescribed fire to control this species, see Fire Management Considerations.

Prevention: Initial steps to prevent the establishment and growth of the clovers in uninfested areas should include limiting or prohibiting their seeding in nearby areas.

It is commonly argued that the most cost-efficient and effective method of managing invasive species is to prevent their establishment and spread by maintaining "healthy" natural communities 89,129 and by monitoring several times each year [67]. Managing to maintain the integrity of the native plant community and mitigate the factors enhancing ecosystem invasibility is likely to be more effective than managing solely to control the invader [63].

Weed prevention and control can be incorporated into many types of management plans, including those for logging and site preparation, grazing allotments, recreation management, research projects, road building and maintenance, and fire management [151]. See the Guide to noxious weed prevention practices [151] for specific guidelines in preventing the spread of weed seeds and propagules under different management conditions.

Cultural control: No information is available on this topic.

Physical or mechanical control: Cutting or mowing the clovers after the flowering stage may provide some control. In a crop production article, the authors reported that the clovers were still capable of setting seed after being cut at about the time of 1st bloom [58]. In a review of cultivation materials, cutting clovers after flowering, cutting plants close to the ground, and cutting plants during drought conditions could lead to decreased abundance of the clover stands [113].

Cultivation is not likely tolerated by the clovers. When annual plowing was compared at various times of the year in Tallahassee, Florida, Japanese clover did not occur in plots plowed in December, February, April, June, or August, although plants did occur on plots plowed annually in October [71].

Biological control: Insect pests and diseases known to attack the clovers in the United States are identified and discussed in the following references: [8,58,93].

Biological control of invasive species has a long history that indicates many factors must be considered before using biological controls. Refer to these sources: [153,162] and the Weed control methods handbook [149] for background information and important considerations for developing and implementing biological control programs.

Chemical control: Very few studies (as of 2010) described in detail the effects of herbicides on clover populations. In Georgia, several herbicides and application timings were tested. In one trial, a single growing-season herbicide application provided good control (up to 99%) of Japanese clover within 2 years of its application in centipede grass (Eremochloa ophiuroides). Herbicides tested in March, before emergence of Japanese clover, provided little to no control [66].

While herbicides can be effective in gaining initial control of a new invasion or a severe infestation, rarely are they a complete or long-term solution to weed management [21]. See the Weed control methods handbook [149] for considerations on the use of herbicides in natural areas and detailed information on specific chemicals.

Integrated management: No information is available on this topic.

Control ⁶

Please contact your local agricultural extension specialist or county weed specialist to learn what works best in your area and how to use it safely. Always read label and safety instructions for each control method. Trade names and control measures appear in this document only to provide specific information. USDA, NRCS does not guarantee or warranty the products and control methods named, and other products may be equally effective.

Description ⁷

Korean and common lespedeza (Kummerowia striata) are introduced, annual, warm-season legumes. Flowers and seeds are borne in the leaf axils at the tips of stems and branches in the Korean lespedeza and in the leaf axils all along the stem in common lespedeza. Two types of flowers are produced. One is readily seen as purple-bluish and the other has no petals and is inconspicuous. Korean lespedeza has a much broader leaflet and stipule than common, and growth is generally larger and coarser. Common lespedeza grows more prostrate. The seed varies from the shiny black of Korean to the stippled seed of common. There are approximately 343,000 seeds per pound of common lespedeza and 240,000 seeds per pound of Korean lespedeza.

Habitat characteristics ⁸

More info for the terms: cover, frequency

The clovers are most common in old fields, pastures, open woodlands, and along roads and stream banks [38,44,49,52,65,139]. Disturbed sites are often habitat for the clovers in recreation areas, wildlife refuges, and state parks. Disturbed sites typically include visitor-use areas, mowed lawns, rights-of-way, fire breaks, boat ramps, and/or parking areas [59,61,62,69].

Japanese and Korean clovers tolerate a wide range of environmental conditions. During a phytosociological study of weedy old fields in Scotland County in North Carolina's Upper Coastal Plain, Japanese clover "did not exhibit an exact affinity to specific edaphic conditions" [128]. Both clovers have been reported in cedar glade communities in the southeastern United States. Cedar glades occur in open areas on calcareous soils and are characterized by high sunlight levels, high summer soil temperatures, and extreme soil moisture levels that range from saturated or flooded to below the permanent wilting point [13].

Climate: The US distribution of Japanese and Korean clovers is limited by climatic tolerances. The northern boundary represents the area at which plants fail to reproduce before the first killing frost, and the western boundary represents areas that receive too little moisture to support the clovers (review by [93]).

Soils: While growth of Japanese and Korean clovers may be best on fertile, well-drained soils [49,93,140], plants survive in a variety of soil textures and in infertile, acidic, or limestone soil types. Both clovers have been reported on dry soils in West Virginia [139], sands in eastern Texas [38] and Missouri [142], sandy loams on the Coastal Plain, and clays in the Piedmont [58]. In the southeastern United States, the clovers grew best on fertile bottomlands, and although described as fairly drought tolerant, plants were most productive in areas with "adequate" moisture [58]. In 2- to 3-year-old fields in South Carolina, production of Japanese clover was greatest (13.5 g/m²) in fields with poorly drained soils (44% silt+clay in subsoil). Productivity was much lower (0.5-2.7 g/m²) on soils with moderate to excellent drainage (9-20% silt+clay in subsoil) [112]. While soil may have been important to Japanese clover abundance, past land use and proximity to a clover seed source were also likely important. Growth of the clovers can also be good on eroded, acidic soils with low levels of phosphorus (review by [93]). A review reports that Korean clover is less tolerant of acidic soils and more tolerant of alkaline soils than Japanese clover (review by [113]).

Two studies monitored the growth of Korean clover in old-field soils with differing textures and moisture and pH levels. Productivity varied on the different soil types studied but not consistently with soil moisture, fertility, or pH. In the greenhouse, germination of Korean clover was nearly 100% on both eroded and intact field soils collected near Ashland, Missouri. At the end of the growing season, however, the average biomass of Korean clover was greater on eroded (108.2 g/m²) than intact (89.2 g/m²) soils. Eroded soils lacked an A horizon and had a clay content that was nearly twice that of intact soils. Eroded soils had lower average growing-season moisture content (10.6%) than intact soils (12.2%). Based on these findings and results from a weeding experiment, researchers concluded that Korean clover was most "competitive" on poor, eroded soils [56]. In southeastern Iowa, Korean clover growth was compared on 3 eroded old-field sites: 2 upland and 1 lowland site (see table below for soil descriptions of these sites). Korean clover established and grew well on all sites, but establishment and growth were best on lowland sites. Available soil moisture during July, the driest growing-season month, was greatest for upland Weller soils. Soil moisture was evaluated in the top 6 inches (15 cm) of soil, where Korean clover roots were confined [16]. Soil characteristics of upland and lowland sites in southeastern Iowa that supported Korean clover [16] Soil type (site) Surface texture Average topsoil depth (inches) Acidity Fertility Bottomland (lowland) fine sandy loam 6-8 moderately acidic fair-medium Lindley (upland) loam 2-4 moderately acidic medium-low Weller (upland) silt loam 4-6 highly acidic medium-low

Flooding: The following studies indicate that both clovers tolerate some flooding but that Japanese clover may be more tolerant than Korean clover. Large Japanese clover populations are common along floodplains in Japan. Along the Ohta River floodplain in Hiroshima Prefecture, Japan, Japanese clover occurred in an area that flooded 3 to 7 times/year but rarely experienced flooding of more than 10 days. Japanese clover's distribution was more closely correlated to soil texture than flooding regime or flooding period. Japanese clover occurred on fine-textured soils and was rare or absent on coarse-textured soils. Japanese clover cover was positively correlated with the percent weight of fine soil particles (r =0.78, P<0.001) [108]. Around Cave Run Lake in northeastern Kentucky, Korean clover occurred on mud flats but not on frequently or infrequently flooded sites, and Japanese clover occurred on mud flats and frequently flooded sites [87]. Growing-season flood frequency or duration during the study period was not reported.

Sources and Credits

(c) Bahamut Chao, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/bahamutzero/2846079946/
(c) Gerrit Davidse, some rights reserved (CC BY-NC-SA), http://images.mobot.org/tropicosdetailimages/TropicosImages2/100217000/19D6A6FC-2FE9-41C7-88FD-588E71F62AAA.jpg
(c) Bruce Ackley, The Ohio State University, Bugwood.org, some rights reserved (CC BY), http://commons.wikimedia.org/wiki/File:Kummerowia_stipulacea_5437576.jpg
Adapted by Kate Wagner from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Kummerowia_stipulacea
Public Domain, http://eol.org/data_objects/24629314
Public Domain, http://eol.org/data_objects/1386481
Public Domain, http://eol.org/data_objects/1386475
Public Domain, http://eol.org/data_objects/24629309

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