Biocontrols for Invasive Plants

Contact: Marc Imlay, Maryland-National Capital Park and Planning Commission (M-NCPPC) | Chair, Bio-Control Working Group of the Mid-Atlantic Invasive Plant Council (MAIPC) | Cell: (301) 442-5657 |

Japanese stiltgrass showing fungal leaf blight Photo Credit: William L. Bruckart III USDA, ARS, FDWSRU

ANNAPOLIS, MD (January 1, 2014) Our tool kit for successful control of non-native invasive plants includes preventing new invasive species from coming in from Europe, Asia, and other continents; manual removal, the use of carefully targeted herbicides, and host specific biological controls.

Classical biological control involves the importation and release of host-specific natural enemies to help regulate pest populations. This strategy is usually used for invasive non-native species that lack effective natural enemies in the region where they have been introduced. In order to avoid direct damage to non-target species, biological control agents must be highly host specific. Agents are brought over after being tested or reviewed for host specificity in their native range and then tested in quarantine conditions in the United States. They are only approved for release if testing indicates a very low likelihood of non-target effects, as determined by the Technical Advisory Group for Biological Control Agents of Weeds (TAG), a group of experts that report to USDA-APHIS. Effectiveness of classical biological control can vary, but of 49 invasive plant projects considered in a recent review (Van Driesche et al. 2010), 27% (13) achieved complete control, 33% (16) provided partial control, and 49% (24) were still in progress. The problem of bio-controls harming non-target organisms was reported to be only about 3% as frequent as before the new rules of proving host specificity went into effect.

For two of the most important invasive plant species requiring control in Mid-Atlantic natural areas, purple loosestrife (Lythrum salicaria), and mile-a-minute weed (Persicaria perfoliata), one or more host-specific insect species have been tested and received permits for release. Three other invasive plant species have had extensive studies conducted on host-specific insects, with petitions for release submitted to TAG, but with proposed releases still under review (TAG Petitions, 2013). These plant species and associated insects are garlic mustard (Alliaria petiolata), the crown-mining weevil (Ceutorhynchus scrobicollis); Japanese knotweed (Fallopia japonica), the psyllid Aphalara itadori; and tree-of-heaven (Ailanthus altissima), the weevil Eucryptorrhynchus brandti.

For some species, biocontrols may already exist in the U.S. in the form of native insects and pathogens that have adapted to the invasive species over time, or non-native species that were accidentally introduced.

Species updates with references for 18 non-native terrestrial and aquatic invasive species are available in the MAIPC Biocontrol Working Group document

One example is:
European Water Chestnut
European water chestnut (Trapa natans) is an invasive aquatic plant native to Europe and Asia. It was first observed in the United States in Massachusetts in the late 1800s. Its current distribution is the mid-Atlantic and northeastern U.S., with the most serious problems being reported for the Connecticut River valley, Lake Champlain region, Hudson River, Potomac River and the upper Delaware River (Swearingen et al. 2010). This species can form dense floating mats, and its sharp fruits can cause painful wounds, making control efforts a challenge. The most promising species for biological control is Galerucella birmanica, a leaf beetle (Ding et al. 2006, 2007), but so far no petitions have been submitted to TAG.

For more information on this and other invasive species in Maryland, visit the Maryland Invasive Species Council

photo available electronically on request.