Efficacy of control measures for European buckthorn (Rhamnus cathartica L.) in Saskatchewan.

Introduced to Saskatchewan in the 1930s as a potential shelterbelt species, European buckthorn is now a prominent understory shrub in riparian woodland and shrub communities around Saskatoon. Locally, the Meewasin Valley Authority (MVA) is actively controlling buckthorn as part of its mandate to conserve natural heritage resources of the South Saskatchewan River Valley, with the goal of restoring the natural biodiversity of remnant patches of native vegetation. European buckthorn is normally dioecious, and MVA has chosen to treat only fruiting stems in an attempt to limit seed production. Two control techniques have been used. In one treatment, glyphosate was applied to stems after cutting; alternatively Garlon 4 Dow AgroSciences herbicide (active ingredient triclopyr) was applied as a chemical girdle directly to the stems using a streamline basal bark spray method. To date, more than 347,000 fruiting stems of buckthorn have been treated. Results indicate good initial progress in limiting seed production in dense buckthorn sites, but at a high cost. Although seed eradication is not a practical short-term goal for the Saskatoon buckthorn population, chemical girdling can substantially and strategically reduce seed and effectively limit spread. Field-tested strategies to reduce costs and improve efficiencies are discussed.