P&PDL Picture of the Week for
January 26, 2009

No Crown Vetch...Now What?

Glenn Nice, Weed Diagnostician, Dept. of Botany & Plant Pathology, Purdue University

For years crown vetch was recommended as a cover crop for the purpose of soil erosion. Several people and governmental organizations planted crown vetch to stabilize areas where soil erosion would likely cause a problem. However, it has been identified as a problem when invading natural areas. Indiana’s Invasive Plant species Assessment Working Group assessed crown vetch and determined that it had a high potential for expansion [2, 3]. This has led to both the Indiana Department of Transportation (IDOT) and the Indiana branch of the National Resource Conservation Service (NRCS) in dropping crown vetch from their recommendations [4]. The web site www.invasive.org, a web site that lists invasive and exotic species describes crown vetch as “Once established it is difficult to remove.”

“Well, if crown vetch is not recommended anymore, what are the alternatives?” This is a question that is often heard when the suggestion of not using crown vetch is proposed. The purpose of using crown vetch is to slow the process of erosion. Crown vetch forms a dense mat of vegetation and a tap root system. This dense mat of vegetation absorbs the energy of the rain and slows surface flow; however, although still fairly effective for erosion control, the tap root system is not quit as effective as a fibrous root system of some of the perennial grass sods. The problem with perennial grasses is that they do not establish quickly.

If the area is new, a place that has had recent disruption, strong slope or a cover crop removed and it is at high risk for erosion, the use of quick fixes may be required. Organic mulches, such as wood fiber and straw, hydro mulch, erosion control blankets or fabrics can be used as short term solutions while preparing to seed a cover crop if needed [5].

In establishing your perennial grass it is beneficial to use an annual grass mix to help stabilize the soils while perennial grasses are being established. In the NRCS Conservation Practice Standard it presently recommends planting legume cool season grass mixtures in the spring from March 1st to May 15th or in the fall from August 1st to September 15th [4]. If a dormant seeding is desired, plant from December 1st to March 1st. NRCS recommends planting a warm season grass and forbs mix from April 1st to June 15th or December 1st to April 1st for a dormant seeding. Legumes suggested are alfalfa, red clover, alsike clover, birdsfoot trefoil, ladino clover and some lespedeza species. Cool season grasses suggested by the NRCS are orchardgrass, tall fescue, smooth bromegrass, timothy, and Kentucky bluegrass. Warm season perennial grasses suggested are bluestems, Canadian wildrye and indiangrass. See the Conservation Practice Standard for specific seeding rates and species growing conditions.

In the crown vetch facts sheet from the Indiana Invasive Plant Species Work Group, alternatives to crown vetch are listed. Roundheaded lespedeza [Lespedeza captiata], purple vetch [Vicia americana], Goat’s-rue [Tephrosia virginiana, Virginia tephrosia], or creeping phlox [Phlox subulata, moss phlox] are reported to be good native alternatives to crown vetch [2].

In the past we have looked to other parts of the world for solutions to problems at home. In some cases this has worked well; for example the introduction of soybean, a plant originally from Asia. However, in other cases, it has not worked out so well. Kudzu was originally introduced to the US from Asia. It had been used in erosion control and as a possible forage [1]. Parts of the country, recently Indiana included, have been fighting kudzu ever since. The intentions were good, but the understanding of the species and how it would adapt to our environment was incomplete. Kudzu, some honeysuckles, Japanese silt grass, and other introduced species (either on purpose or accident) have been identified as problematic and have fallen under the category as being “Invasive Species.” In the case of plants, the very characteristics that make the plant desirable, ability to grow well, tolerate a wide variety of growing conditions and ability to take a gamut of abuse, can also make the plant invasive. For a list of invasive plant species in Indiana see either the Indiana Cooperative Agricultural Pest Survey’s web site [http://extension.entm.purdue.edu/CAPS/] or the Weed Science Page [http://www.btny.purdue.edu/weedscience/].

References:

1. R.Y. Bailey. 1939. Kudzu for erosion control in the southeast. Farmers Bulletin No. 1840. USDA.

2. Invasive Plant Species Assessment Working Group. 2006. Crown Vetch Coronilla varia: Invasive Plant Species Fact Sheet.

3. Invasive.org. Accessed 1-20-2009. Crownvetch.

4. NRCS. Natural Resources Conservation Service Conservation Practice Standard: Conservation Cover. pp. 327-1 to -8.

5. Anonymous. Accessed 1-21-2009. Soil Erosion Control: Mulches, Blankets and Mats. Minnesota Urban Small Sites BMP Manual. (pdf file)

Click image to enlarge

crown vetch

crown vetch flower

crown vetch closeup

All images taken from Invasive.org

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service