Status of biological control in vegetation management in forestry

Biological control traditionally depends upon importing the natural enemies of introduced weeds. Since vegetation management in forestry has primarily been aimed at protecting economic species of trees from competition from other native plants, biological control has been of little use in forestry. An alternative approach to controlling unwanted native plants, supplementing their existing complex of natural enemies with introduced insects found attacking closely related plants, is being used on rangeland, but is not recommended for forestry. New agents will not remain restricted to the location where they are released, but will spread and would eventually affect the target plant throughout its entire range, including areas where it might be desirable. A more promising alternative is manipulating one or more insects or diseases that already attack the undesirable plants. Many plant pathogens naturally associated with a particular plant species are highly virulent and specific to only the target plant. Mass producing these pathogens and applying them with conventional spray systems is being used in agriculture and is being considered for forestry. Other methods of manipulation, such as mass rearing insects and releasing them to attack the undesirable plant or manipulating populations of the insect predators that naturally suppress phytophagous insects of a target plant, are discussed.