Biological control involves the use of living organisms, such as insects, to control a weed infestation, and attempts to recreate a balance of plant species with predators. Since many noxious weeds of most serious concern in rangeland are exotic species, they have few established natural predators. Bio-control research focuses on introduction of natural predators from the weed's area of origin onto local plant populations. Bio-control methods generally suppress host weed populations, but will not contain or eradicate them; therefore containment with another method is a critical component of this type of management. It is most effective on dense weed infestations over large areas. These insects are not adaptable to all sites; therefore evaluation must be used to find where they will be most effective. Contact your local weed professional for help with this type of management. Often bugs can be released for a nominal fee (if any) in your county through your county weed district. Leafy spurge currently has several insect species cleared for use in the United States, and Flea beetles (Aphthona spp.) seem to be showing the most promise at this time. Two gall flies and a seed head weevil and a root-boring beetle have established effectively on spotted knapweed in western Montana.
State-listed weeds that biocontrol agents are currently available for: Canada thistle, spotted knapweed, Dalmatian toadflax, tansy ragwort, St. Johns Wort, leafy spurge, purple loosestrife & diffuse knapweed. (* Currently APHIS has initiated research based biocontrol for salt cedar, with anticipation of approved permitting in the future.) For more information on biocontrol please contact Tonda Moon at tmoon@mt.gov.