Black henbane is a poisonous, invasive plant in the family Solanaceae, and is typically associated with highly disturbed environments, such as pipelines, roadsides, and mammalian burrows. Often, such disturbances require reseeding for successful restoration; thus, the potential exists for competition between henbane and perennial grasses commonly used in restoration projects. These competitive interactions have not, to our knowledge, been evaluated. We conducted a greenhouse study to compare the response of henbane when grown alone and in combination with three common, cool season, perennial, northern mixed prairie grass species. We examined both seedling and mature grass response to the presence or absence of henbane and the response of henbane to the grasses. Using the relative neighbor-effect index, black henbane was found to be a very poor competitor with mature grasses and two out of three seedling grasses tested. All measures of henbane growth were significantly lower among plants grown with a mature grass pot companion. Total biomass of henbane was up to 99% lower when grown with mature grasses. Mature grasses were not negatively affected when grown in combination with henbane. Western wheatgrass (Pascopyrum smithii) was the only seedling grass that was competitive with henbane but was also the only seedling grass negatively affected by henbane in both biomass and tiller production. These experiments suggest that henbane is not well suited for invasion of mature grass stands but may negatively influence some perennial grass seedlings in restoration situations.

Nomenclature: Black henbane, Hyoscyamus niger L.; western wheatgrass, Pascopyrum smithii (Rydb.) Á. Löve

Interpretive Summary: Black henbane is a poisonous, invasive annual or biennial in the family Solanaceae that appears to be an opportunistic invader, proliferating when competition is minimal. Black henbane can be successful in situations with limited competition and high nutrient and moisture availability. As such, henbane tends to be associated with disturbed conditions in which reseeding of native vegetation may be required. Revegetation with perennial grasses is an excellent method for long-term control of invasive plants but is often species and site specific. The results from these experiments indicate that black henbane is a poor competitor with Sandberg bluegrass and Idaho fescue seedlings, but it does negatively affect western wheatgrass seedlings. However, once established, all three grasses strongly suppressed henbane. For reclamation efforts along disturbance corridors, such as gas lines where black henbane often appears, multiple grass species may be effective in suppressing henbane.