Efficacy of Control Measures for European Buckthorn (Rhamnus cathartica L.) in Saskatchewan

Abstract

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.

The biology of Canadian weeds. 139. Rhamnus cathartica L.

“…Populations are more scattered in the western provinces (Maw 1984) but it is spreading to new locations in Alberta (E. Beaubien, personal communication). It is found in the Souris River Valley in southeast Saskatchewan where it is contiguous with the US midwestern populations centred in Minnesota and extends for nearly 80 km along the South Saskatchewan River but centred in Saskatoon (Delanoy and Archibold 2007). It is also common in suburban and urban areas of southern Manitoba ).…”

“…In more compact soil, R. cathartica seedling density was reduced to 74 seedlings m (2 , but it was still dominant compared with other species (Archibold et al 1997). Delanoy and Archibold (2007) reported a halving in buried-seed density in 10-cm-deep samples from plots treated by removal of female trees in previous years through herbicides applied to cut stumps.…”

“…White et al (1993) suggested that R. cathartica could continue to spread in the future, owing to its proven ability to invade a variety of habitats. Serious concerns about the continued spread of R. cathartica, have been raised across Canada, including Edmonton, AB (E. Beaubien, personal communication), the Saskatoon area, SK (Archibold et al 1997;Delanoy and Archibold 2007) and the Ottawa area, ON (White et al 1993). Catling (1997) reported that R. cathartica, naturalized in invading forests in Ontario, can become the dominant understorey vegetation in some cases; thus creating a major threat to native biodiversity.…”

“…One reason postulated for this result was that R. cathartica produces leaf litter with a relatively low C:N ratio, which decomposes rapidly (Heneghan et al 2002). Heneghan et al (2002) found that leaf litter was completely lost from litter bags within 2 mo in an urban woodland where earthworm activity was high and R. cathartica Holmgren et al (1990)] and on data from Hamilton (1943), Scoggan (1978), Botham (1981), Webber (1984), Catling et al (1985), Hinds (1986), Frankton and Mulligan (1987), White et al (1993), and Delanoy and Archibold (2007). The plants in Edmonton were collected from a ruderal area in 2005 by Elizabeth Beaubien and their identity was confirmed by Paul Cavers.…”

“…Cutting or girdling of a single stem before applying glyphosate or picloram/2,4-D usually resulted in the death of the entire shrub, thereby potentially saving time and money. Delanoy and Archibold (2007) treated over 347 000 fruiting stems of R. cathartica in Saskatoon in an attempt to limit seed production. Two treatments were employed; in one, glyphosate was applied to stems after cutting, in the second a herbicide with triclopyr as the active ingredient was applied as a chemical girdle to stems using a streamline basal-bark-spray method.…”