UPDATE: The State of Oregon Department of Agriculture has prepared a list of pertinent information regarding the current situation with biocontrols in Oaks Bottom. Please visit http://www.portlandoregon.gov/parks/article/541121 for additional details and contact information.
Invasive purple loosestrife has been abundant in the Oaks Bottom Wildlife Refuge for years, as it is in wetlands across the country. Ten years ago, Environmental Services and Portland Parks and Recreation started working with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service on biologic controls.
invasive purple loosestrife thrives in some parts of Oaks Bottom
They released leaf beetles that feed exclusively on purple loosestrife. For several years, high water in Oaks Bottom flooded the beetles in May and June before the invasive plants grew high enough to keep the insects above water.
adult leaf beetles feeding on purple loosestrife at Oaks Bottom
In the last two summers, city staff noticed that more leaf beetles survived and consumed more purple loosestrife. This summer, it looks like they’re finally getting to eat all they want. In some areas, loosestrife plants are completely defoliated. If low water and dry conditions continue, defoliation could increase tenfold this summer.
purple loosestrife in the southwest corner of Oaks Bottom after a leaf beetle feeding frenzy