The objectives of the study were: 1) to evaluate the relative efficacy of available biological controls for thimbleberry and associated hardwood species; 2) to measure the interactions among thimbleberry, overstory hardwoods, and conifer seedlings; 3) to evaluate the direct and indirect effects of selected biological control agents on conifers and other non-target vegetation; and 4) to determine if these agents are viable options by themselves or in conjunction with other control methods. Fungi associated with diseases of forest weed species were tested for their mycoherbicide potential under greenhouse, growth chamber and field conditions. Several field treatments were applied, and subsequent changes to competing vegetation were measured in terms of follar disease ratings and percent cover estimates.