Tillamook Soil and Water Conservation District and Oregon State Parks are testing the use of Hylobius weevils to control purple loosestrife at The Wetlands Conservancy’s Doris Davis Wetland Preserve in Manazanita. The long-term objective of biological control is to reduce the abundance of loosestrife’s impact on wetland flora and fauna. Purple loosestrife crowds out native vegetation, often creating a monoculture. In addition to the loss of native biodiversity, purple loosestrife harms waterfowl nesting habitat, reduces water flow and quantity and can have negative impacts on some amphibians.
Hylobius transversovittatus is a root-boring weevil that deposits its eggs in the lower stem of purple loosestrife plants. Once hatched, the larvae feed on the root hairs and then burrow into the root tissue, destroying the loosestrife’s nutrient source for leaf development. The adult weevils emerge in the spring and will feed on the leaves of loosestrife which in turn leads to the complete destruction of mature plants. The entire life span of the weevil can be up to 5 years which makes it a great biological control agent.
Oregon State Parks Youth Conservation Corps worked with Tillamook Soil and Water Conservation and The Wetlands Conservancy staff and neighborhood volunteers to remove 1260lbs of purple loosestrife biomass (three truckloads) and released 400 Hylobius weevils at Doris Davis Preserve July 23-24.2018. Over the next few years, we will continue to manually remove the loosestrife as the weevil population establishes and hopefully becomes the primary control agent.