CROWN VETCH (Securigera varia) IS A NON-NATIVE PERENNIAL PLANT IN THE LEGUME FAMILY. It was introduced into the United States in the 1950s primarily for erosion control along roads and waterways. Crown vetch is currently found in all US states except North Dakota (USDA Plants Database 2015, Klein 2011).
The invasion of crown vetch into natural areas in Midwestern states is having a significant impact on plant diversity and wildlife habitat. The plant is a prolific seed producer, spreading by seed and rhizomes.
Field trials were conducted in 2007 on a crown vetch infestation located on Boomerang Island in the Upper Mississippi River National Wildlife and Fish Refuge in Wisconsin. Lee Shambeau with 4 Control Inc. applied Milestone® specialty herbicide at 5 fluid ounces per acre (fl oz/A) in August with a backpack sprayer to mature crown vetch plants. Visual evaluations taken three weeks after treatment showed greater than 95 percent control of crown vetch with no damage to desirable trees and shrubs.
In 2015, refuge Biological Science Technician Calvin Gehri evaluated the site to determine if crown vetch had reinvaded. The site had not been treated since 2007 and Gehri reported that control remained good to excellent. Crown vetch cover was about 10 to 15 percent (85 to 90% control) eight years after application compared to greater than 90 percent cover prior to treatment in 2007.
Reed canary grass (Phalaris arundinacea) and nettles (Urtica dioica L.) currently occupy niches once dominated by crown vetch. Although neither plant is considered to be desirable, nettles allow other native plants to establish and are used by some native butterflies. Both reed canary grass and nettles provide competition that minimized crown vetch re-invasion. Depending on habitat objectives, establishing desirable plants may be a consideration with future control efforts.
Other Field Studies
Dr. Mark Renz of the University of Wisconsin conducted field trials near Barneveld, Wisconsin to study efficacy of Milestone® specialty herbicide applied to crown vetch at three growth stages. Milestone was applied to crown vetch at the bud (June), flower (July), and fall (October) growth stages in 2012. Evaluations included visual percent control and cover of crown vetch, and percent visual injury to grasses one to two years following treatment.
Results of the study showed that Milestone applied at either bud or fall growth stage provided excellent control one year after treatment (Figure). However, only the fall herbicide application continued to provide good crown vetch control two growing seasons following treatment. There was no grass injury noted in plots resulting from the herbicide treatment.
These results indicate that Milestone applied at either 5 or 7 fl oz/A will provide good to excellent control when applied late summer or fall. Establishing a competitive plant community is critical to maintain long-term control of the weed. Follow-up herbicide applications may be necessary to control seedlings emerging from the soil seed bank or mature plants that survive treatment. Disturbed sites or areas without desirable understory vegetation may require restoration. In areas with residual desirable vegetation, post-treatment restoration efforts may not be necessary.
Klein, Helen. 2011. Crownvetch Coronilla varia L. Alaska Natural Heritage Program. Univ. of Alaska, Anchorage. http://aknhp.uaa.alaska.edu/wp-content/uploads/2013/01/Coronilla_varia_BIO_COVA2.pdf
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