Could it be the End of Flowering Rush?

On June 21, 2013 approximately 183 acres along the shores of Big, Little Detroit and Deadshot Bay (Curfman) were treated in a attempt to control Flowering Rush (FR).  Fourteen more acres were treated in the City’s beach area in the Park and along West Lake Drive.   Additional treatments took place in Lakes Melissa and Sallie.

The treatments were paid for by taxpayers under the auspices of the Pelican River Watershed District (PRWD) and the City of Detroit Lakes. The actual treatments were carried out by Professional Lakes Management (PLM), authorized and supervised by the Minnesota Department of Natural Resources.     

 

Flowering Rush was first observed in these waters in 1976.   Some insist that the plant was set along the shore of Deadshot Bay (Curfman Lake) as part of a residential landscaping effort.   No one has provided any direct knowledge of that act, but genetic research indicates that our FR is derived from nursery stock.  

Even in the late 1970’s Deadshot Bay residents realized that Flowering Rush was a problem and began hand-pulling.   It did not take long to learn those efforts were not solving the problem, so residents turned to the PRWD for help.   In the late 1980’s for at least two years District staff  used both granular and spray forms of an aquatic version of Roundup (glysophate) to treat FR in Detroit and Sallie,  especially in Deadshot Bay,  and near Long Bridge and other beaches where there were heavy infestations.    Though permitted by DNR, the approach was considered unsuccessful. 

Hand-pulling continued into the early nineties, sometimes by teams recruited by Lake Detroiters and other groups.   Also, because of the plant’s flowering habit and the expectation that the plant was spreading via seeds from the flowers, some efforts were made to remove the plant’s flowers during their July blooming period.  (Later it was discovered that our FR seeds were sterile, and the plants spread entirely by root fragment growth or dispersal.)

In the meantime Detroit residents petitioned the District for a project to buy a machine to harvest FR. Some mechanical harvesting had occurred using borrowed equipment in before, but new harvesting equipment was deployed in 1991, and it was used largely for FR management until 2005.   At its peak in 2002, just over 1600 tons of plant debris, mostly FR, was removed from the lake. 

The harvesting strategy was adopted because of the view, reinforced by some experts, that multiple harvest of FR stems would deprive the root mass of energy.   This was an approved strategy by the DNR, and even as recently as 2010, was their recommended method of FR control.

Except that by 2002 District staff had come to the conclusion that though the harvesting equipment provided some aesthetic relief from the scourge of FR, it did not offer a significant amount of control of the plant, nor did it prevent the spread of the nuisance.       

In 2003 the District began testing several herbicides with six test sites on Big Detroit and Dead Shot Bay.   Nearby control sites were employed to evaluate the testing.  During the following year, some additional sites were used for other herbicides.   Different chemical formulations and different application methods were used.  Though results were inconclusive the District was allowed for several more years to do some more extensive treatment with Imazypyr on emergent stands of FR.   Some control was obtained, but emergent plants in deeper water, and submerged plants were unaffected and continued to spread.     

In 2009 PRWD held a public meeting to obtain input from almost 100 citizens and local officials.   As one outgrowth from that effort the District called together experts from across the nation for a meeting in St. Paul to consider further treatment strategies.   That meeting led to District-initiated multi-pronged research on the nature of FR and some alternative treatment efficacies.    A collaborative effort involving Mississippi State University Institute of Geosciences, the Army Corps of Engineers, and Concordia College (Moorhead), supported by the taxpayers of the District, the City of Detroit Lakes, and the Minnesota DNR, was carried on in 2010, 2011 and 2012, and led directly to last week’s expanded treatment program utilizing the herbicide Diquat.    On-going research on treatment impacts on Flowering rush and native aquatic plants directed by Dr. John Madsen of Mississippi State Geosciences Institute will continue  with funds provided by PRWD.  

RDH

06/28/13