Flowering Rush Project

Testing flowering rush removal techniques in Lake Minnetonka

City:

Project Status: 
Completed
About this project: 

Plan
The flowering rush pilot project attempts to remove and control the aggressive, non-native plant flowering rush (Butomus umbellatus) without the use of herbicides. The MCWD has hired contractors remove the invasive plant by hand on a limited number of bays on Lake Minnetonka. In 2011 the study focused on Maxwell Bay and Smith's Bay; in 2012 it focused exclusively on Smith's Bay. 

Narrative
Flowering rush (Butomus umbellatus) is a perennial native to Asia and Europe found typically along shorelines of streams and lakes.  Stems, leaves and flowers usually grow above the water's surface, but can be found submersed.  The plants have an umbrella-shaped pink flower that is arranged in an umbrella-shape.  The plant reproduces through rhizomes (underground stems), the production of buds or tubers, or from flower buds.  Flowering rush competes with native vegetation by aggressively growing in dense populations. It displaces native plants, impedes boat passage, and interferes with swimming.

Flowering rush has been in Lake Minnetonka since it was first identified in 1976 by the Three Rivers Park District in Maxwell Bay.  In 2009, another survey completed by the Minnesota Department of Natural Resources (MnDNR) identified the plant in nine bays of Lake Minnetonka and 4 locations in Minnehaha Creek. 

In order to manage the spread of the invasive plant and to determine if it could be controlled without the use of herbicides, MCWD hired Waterfront Restoration, LLC to hand remove flowering rush at two test sites on Lake Minnetonka. 

Technical Summary
In cooperation with MCWD, Waterfront Restoration, LLC obtained authorization from land owners of lakefront property in work areas to obtain Minnesota Department of Natural Resources permits for plant removal.  Flowering rush was identified and carefully extracted by hand at the test sites, making sure to collect all parts of the plant.  The extracted plants were placed in 50-pound capacity bags.  Waterfront Restoration used custom floating nets encircling the test sites, trapping any floating plant fragments that may have escaped during the removal process.  Pre- and post-plant surveys of the test sites were completed by Blue Water Science.  Sediment analysis was collected pre extraction by Blue Water Science.  Waterfront Restoration removed approximately 9,000 wet weight pounds of flowering rush from the test sites.  It is believed that approximately 95% of the stems, rhizomes, and bulblets were extracted. 

In Spring 2012, a follow up survey was conducted by Steve McComas of Blue Water Science along with staff from Waterfront Restoration, and it was concluded that a highly detailed hand removal process was successful in reducing the population of Flowering Rush in soft substrates. In harder substrates, such as those with gravel and rock, hand removal did not prove effective with nearly all the plants coming back the next year. In the two sites with soft substrates, one had approximately 80% control while the other had nearly 95 percent control. Follow up extraction will likely happen on those two sites again in 2012. Also, the MCWD plans on having a survey in done in 2012 to better understand the population of Flowering Rush in Lake Minnetonka, and will give us the baseline data needed to monitor if Flowering Rush is spreading, and how fast it is spreading.