Private landowner participation in management initiatives can be encouraged by interventions, which must resonate with the underlying subjective motivations of the landowners. In this study, we use the Theory of Planned Behavior to gauge the relative influences of (1) attitudes; (2) subjective norms; and (3) perceived behavioral control on landowner intentions to harvest trees threatened by invasive insects. We use a survey (n = 696) to estimate the effects of these latent factors among family forest owners in New England. Our results suggest that, overall, normative pressures are the dominant influence on landowners’ harvest intentions. However, for certain subgroups, such as those with especially high levels of knowledge and experience with forest insects, or those with forestry experience, attitudes are dominant. Perceived behavioral control was not revealed to be dominant among any of our subgroups. These findings can be used to inform landowner interventions that are differentiated by landowner type.