The invasion of crown vetch into natural areas, such as prairie grasslands, barrens, and dunes in midwestern states, is having a significant impact on native plant diversity. The plant is a prolific seed producer and spreads by seed and vegetatively by rhizomes. Crown vetch is capable of spreading over small trees, shrubs, and grasslands eventually forming large single-species stands that modify soil nutrient levels and alter fuel loads in fire-adapted ecosystems. The plant tolerates a wide range of environmental conditions, but grows best in areas with 18 inches or more precipitation.
Crown vetch has diffuse stems that spread up to about six feet in length and three feet tall. Leaves are dark green and odd-pinnately-compound, with 9 to 25 leaflets per leaf. Roots are multi-branched with fleshy rhizomes. The plant flowers from late spring through summer; individual flowers are pea-like and vary from pinkish-white to deep pink in color. Seed are produced in slender, linear, jointed pods (loments) that may reach two inches in length. The length of time seed remain viable in soil is unknown, but high soil seed banks have been reported.
The key to the successful control of crown vetch is to prevent new infestations or control them as soon as possible. Careful pulling or digging the entire plant—including roots, followed by removal of any new seedlings in successive years, can be successful on very small infestations. There are no available biological control agents for crown vetch.
Large infestations of crown vetch are best controlled with an integrated management approach. Milestone® at 5 to 7 fluid ounces per acre (fl oz/A) should be applied to crown vetch at the vegetative growth stage prior to bloom. The higher rate of 7 fl oz/A is recommended at later growth stages. Removal of top growth by pulling, mowing or burning followed by an herbicide application to regrowth may improve control. Follow-up herbicide application may be necessary to control seedlings emerging from the soil seed bank or older plants that survive treatment. Disturbed sites or areas without desirable understory vegetation may require restoration to create a competitive desirable plant community and improve the potential for long-term control. In areas with residual desirable vegetation, post-treatment restoration efforts may not be necessary.
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Active ingredients for herbicide products mentioned in this article: Milestone (aminopyralid).