Crown vetch (Securigera varia) is a perennial legume introduced from Europe, Asia, and Africa. Starting in the 1950s, it was widely planted to stabilize soil and control erosion, particularly along highways and steep embankments. This ornamental plant quickly became an aggressive invasive species, forming dense, sprawling mats that smother native vegetation. Control is difficult due to its persistent, multi-branched root system, which includes extensive rhizomes that can spread up to 10 feet horizontally. Systematic removal is necessary because a single plant can colonize up to 100 square feet within four years.
Identifying Crown Vetch and Its Root System
Crown vetch is recognizable by its dark green, compound leaves, which are fern-like and consist of 11 to 25 small, oblong leaflets. It produces distinctive pea-like flowers clustered in a globe-like shape, ranging from pink and lilac to white. These clusters bloom on long stalks from late spring through August.
The plant’s invasive success is driven by its network of aggressive rhizomes, which act as anchors and storage structures for energy reserves. This extensive root system makes complete manual extraction labor-intensive, as any small fragment left behind can sprout into a new plant. Crown vetch also reproduces prolifically by seed, which can remain viable in the soil for several years, compounding the challenge of long-term eradication.
Non-Chemical Removal Techniques
For small, isolated patches, manual removal requires diligent effort to extract the entire root crown and all attached rhizomes. Using a pitchfork or similar tool to loosen the surrounding soil can make the process easier. All removed material, especially if flowers or seed pods are present, should be bagged and disposed of to prevent seed spread.
Mechanical control through repeated cutting or mowing aims to deplete the root energy reserves over time. Mowing should begin in late spring and be repeated at least three times throughout the growing season for two to three consecutive years. It is important to mow before the plant flowers to prevent the production of new seeds.
Smothering uses solarization to suppress growth and kill seeds near the soil surface. This involves covering the infested area with a clear plastic sheet for four to six weeks during the hottest months. The soil must be kept moist, as the combination of high temperature and moisture kills weed seeds and shallow perennial tissue. Solarization is less reliable for deep-rooted structures like crown vetch rhizomes.
Targeted Herbicide Application
For large or well-established infestations, chemical control is often the most efficient method for complete eradication. Systemic foliar-applied herbicides move through the plant’s vascular system into the extensive rhizome network. The most effective time for application is late summer or early fall, when the plant is actively moving resources down to the roots for winter storage.
The recommended active ingredients are triclopyr and glyphosate, typically used in a 1% to 2% solution mixed with water. Triclopyr is a selective, broadleaf-specific herbicide, making it the preferred choice where desirable grasses are intermingled. Glyphosate is a non-selective option that affects any plant it contacts, requiring precise application to avoid damaging neighboring vegetation.
Application should cover the leaves and stems to the point of runoff. Including a non-ionic surfactant will significantly improve the herbicide’s effectiveness. Spot treatments are suitable for smaller areas, while broadcast applications are necessary for dense infestations. Repeated applications over several years are required to eliminate surviving root fragments and control new seedlings from the persistent seed bank.
Maintaining the Site After Eradication
Long-term monitoring and site restoration are necessary due to the persistent seed bank. Once the vetch is removed, prepare the disturbed soil for new planting to prevent re-establishment. Crown vetch fixes nitrogen, which alters soil chemistry, so select new plants that thrive in the current conditions.
Establishing a competitive cover of desirable, native plants is the most effective long-term strategy for preventing the return of crown vetch. These plants can fill the void and suppress the germination of new vetch seeds. For the first few years following treatment, routinely check the site for re-sprouts or new seedlings, addressing them immediately. Consistent monitoring and establishing a robust plant community secure the site against re-infestation.