Conclusions
Once an invader reaches a high level of abundance eradication becomes very difficult or impossible. This means that time and resources are continually required to manage widespread invaders. Native pathogens could provide a low cost method for controlling some invaders if effective pathogens can be identified (Kotzé et al. 2015). Using our proposed framework, we aim to help predict what invaders are most susceptible to pathogens and therefore have the potential to be managed with native pathogens. This management can be accomplished with bioaugmentation of pathogens as microbial herbicides, a method that is currently used for a limited number of native pathogen-invasive plant combinations (Trognitzet al. 2016).
As debate continues surrounding the idea that native pathogens can control invasive plant populations and possibly reverse negative ecological effects, we suggest that a better understanding of the factors that predispose invaders to pathogen decline will improve monitoring and management efforts (Flory et al.2018; Policelli et al. 2018). Plant traits can determine pathogen tolerance and resistance to disease, so, logically, invader traits should provide some power to predict pathogen accumulation. There are many traits that are correlated with susceptibility of plants to disease, but more studies are needed assessing the interspecific variation in traits and plant pathogen attack, particularly among invasive species. We found evidence for 20 cases of invasive plant impacts due to novel pathogen interactions, but we expect that there are additional cases that remain unidentified due to limited research, for example where the etiology of disease has not been identified as with most plant-soil feedback studies (Diez et al. 2010). Additionally, most of these examples were variable in their effects on invader populations in the field so it is possible that cases with insufficient population monitoring of invaders may be overlooked. These cases could be important for management from a bioaugmentation perspective, where native diseases are augmented on susceptible invaders to provide control. As long-term research on invasive plants accumulates, this framework allows us to leverage these data to better understand patterns in dynamics of novel interactions with pathogens and their potential to control invader populations.