The Arboretum is also using biological control to manage insect pests and diseases. Some examples currently in use are: 1) predatory nematodes (Steinernema sp.) to control Iris borers and cutworms; 2) predatory wasps to control whiteflies and predator mites to control spider mites in greenhouses; and 3) antagonistic fungi (Coniothyrium minitans) to control sclerotinia whitemold in annual flowers. When biological control is not effective, Arboretum staff turns to other non-toxic forms of pest control, such as microbial insecticides, insecticidal soaps and horticultural oils. More information on environmentally-friendly pest control can be found at the pest information center in the Arboretum's Home Demonstration Garden.
Purple Loosestrife is a native plant of Eurasia that has invaded Minnesota wetlands and lakeshores. It effectively chokes out cattails and other native wetland plants and reduces habitats for wetland animals. The Arboretum has introduced two species of beetles that are parasitic to Purple Loosetrife, feeding on its leaves and flowers. While the beetles do not eliminate Loosestrife completely, they significantly reduce its population and keep it from taking on a dominant role. The impact of these beetles on non-target species and the natural ecosystem is minimal, and beetle populations decline with Loosestrife reduction.
First brought to Minnesota from Europe in the mid-1800s, buckthorn is an invasive species that overtakes natural areas and crowds out more desirable species and native vegetation. It is shade- and drought-tolerant and quickly invades woodlands and the edges of prairies and fields. The Arboretum, in conjunction with the Minnesota Department of Natural Resources and Dow AgriSciences, initiated a model buckthorn control project in the 1990s that used an herbicide called Garlon 4. Today, the Arboretum is working closely with researchers from the University of Minnesota to develop a biological control plan to combat future buckthorn infestations without chemical herbicides.
Leafy Spurge, an aggressive deep-rooted perennial, is native to Eurasia. It produces a milky latex-like substance that is poisonous to some animals and a skin irritant to humans. Two species of beetles have been released at the Arboretum to biologically control Leafy Spurge. Biological control is used in conjunction with fall herbicides and spring burning in an integrated management approach to Leafy Spurge control. The long-term goal of the Arboretum's management plan is to replace the Leafy Spurge-infested areas with native grasses and forbs.
Garlic Mustard is a biennial flowering herb that, once native to Western and Central Asia, was introduced as a culinary herb to the United States in the 1860s. It is classified as an invasive species in eight states-including Minnesota- because of its ability to spread into undisturbed plant areas and harm fungi that are vital to tree growth. Currently, Arboretum staff pull out all garlic mustard plants at first sighting. Research is currently underway at the University of Minnesota to develop a biological control plan that will eradicate or significantly reduce populations of garlic mustard at the Arboretum.