Krenite (fosamine ammonium) is a foliar herbicide that primarily targets woody plant species, however formal evaluations of its efficacy and potential for non-target impacts are scarce in the literature. The few tests that exist of Krenite focus primarily on its use in open environments, and the value of Krenite in controlling invasive understory shrubs is unclear. Here, we test the impact of Krenite on invasive Common Buckthorn (Rhamnus cathartica L.) and co-occurring herbaceous plants across six forest sites in Minnesota, USA. Buckthorn treated with Krenite had a 95% mortality rate, indicating high efficacy of Krenite for use against buckthorn. Non-target impacts varied between forbs and graminoids such that forb cover was reduced by up to 85%, depending on site, whereas graminoid cover was sparse and impacts of Krenite on graminoids were unclear. These results indicate that while Krenite can provide effective control of buckthorn and other understory shrubs, there is potential for significant non-target impacts following its use. We therefore suggest that land managers carefully consider the timing, rate, and application method of Krenite to achieve desired target and non-target impacts.