Iris pseudacorus is an aggressive aquatic plant that has invaded riparian areas in many states across the U.S. However, Iris pseudacorus has only been detected in three locations in Oklahoma – in a highway ditch, on the shore of a manmade reservoir, and in a wetland associated with one of Oklahoma’s scenic rivers. We have an opportunity to control the iris at the critical wetland site, which is privately owned, but part of the Oklahoma Natural Areas Registry program. The site contains an area of approximately 3 acres of a near monoculture of Iris pseudacorus with several scattered iris clumps in and near spring fed tributaries of the Blue River. We collected baseline vegetation data from two 70 m long transects in the growing season of 2007.
In April of 2008, collaborating with Jona Tucker of The Nature Conservancy, we treated part of one transect with two aquatic labeled broadband herbicides (imazapyr and glyphosate). We applied the herbicide using a wick type applicator to both cut and uncut iris leaves.
During the 2008 growing season, we continued vegetation data collection on transects and evaluated the kill rate of the four herbicide/cutting treatments. To photo shows the untreated iris (in lower left corner) and treated iris (to the right of it) two months after application. Results from this preliminary treatment will determine the treatment method for the remainder of the iris infestation.
In November of 2008, we found that the imazapyr treated areas were devoid of any iris, including new shoots. The glyphosate areas had significant resprouting. There appeared to be no difference in cut or uncut areas. Therefore, we are able to reduce the labor by not cutting. Our plan to treat the entire infested area early in the growing season of 2009 was hampered by an excessively wet spring. We continued to monitor the area and plan to treat the infestation in 2010.
In the Summer of 2009, we surveyed via kayak along the Blue River for invading iris. We found several patches downstream from the site. However, none were as extensive as the monoculture found at our study site.