Control

Management and Control

In some areas of the east and midwest (especially near urban areas) buckthorns and other invasive shrubs (e.g. Eurasian Lonicera spp.) have taken over the understory of entire woodlots, replacing native shrubs and tree saplings. On these sites introduced shrubs may be the only remaining nesting sites for some woodland birds (Schmidt and Whelan 1999). In situations where native shrubs are absent or nearly so, buckthorn could be removed in sections, releasing native shrubs. Native shrubs can be planted if they have been greatly reduced or eliminated from the site.

Archibold et al. (1997) recommend removing the largest seed-producing (female) buckthorn plants first, to reduce or prevent new seeds from being added to the seed bank.

Manual Control

For small populations or single plants.

Cutting: Simply cutting down buckthorn will result in vigorous resprouting and regrowth, so cutting is best followed up by immediately painting or spraying herbicide on the cut stump (Heidorn 1991, Archibold et al. 1997). See "Chemical Control" below.

Girdling: Girdling is widely used on mature buckthorn and will usually kill the plants. Heidorn (1991) suggests using an axe or a saw to cut two parallel lines around each stem, about 10-12 cm apart. The outer bark in between these two lines should then be peeled off. The stem should be checked after a few weeks to make sure that bark did not grow across the gap, and any new sprouts should be cut.

While water and minerals continue to be transported upward into the foliage, girdling prevents the sugars produced by the leaves from being transported down to the roots. Eventually the roots starve, killing the entire plant. Large plants with significant food reserves stored in their roots may take a year to succumb, though.

Digging and pulling: Buckthorn seedlings have shallow root systems, and first-year seedlings in particular are easily hand-pulled. Older, larger plants are of course much tougher to remove. Hoffman and Kearns (1997) state that as a rule, small plants up to 1.3 cm (0.5 in) in stem diameter can be pulled when the soil is moist, while plants 1.3-3.8 cm (0.5-1.5 in) in diameter can be dug or pulled with a weed wrench. Plants larger than about 3.8 cm (1.5 in) may present a significant challenge for the weed warrior. After digging or pulling plants, disturbed soil should be tamped down, to reduce seedling establishment.

Chemical Control

The best time for chemical control is in the fall, when native plants are entering dormancy and Eurasian buckthorns (and honeysuckles) are still green and growing (Heidorn 1991, Hoffman and Kearns 1997). At this time, buckthorn plants are easily spotted and recognized. They are also still highly susceptible to herbicides, while the native vegetation is resistant to most herbicides by this time. Winter herbicide application to the basal area has also been successful in controlling common buckthorn.

Cut stump treatment: Archibold et al. (1997) found that immediately painting or spraying the cut stumps with 1:1 solution of water and glyphosate ("Roundup", or "Rodeo" for spraying over water) was 94% effective in killing the plants. A 1:1 solution of triclopyr ("Garlon 4") was 70% effective. In both cases the plants that survived produced only short, stunted shoots by the end of the growing season. "Killex" or "Trimec" (a mixture of 2, 4-D, mecoprop, and dicamba) was ineffective in preventing resprouting.

Hoffman and Kearns (1997) recommend a 20-25% active ingredient (a.i.) solution of glyphosate, or a 25-50% a.i. Solution of triclopyr, as stump treatments. Alternatively, they recommend basal bark application of 6% a.i. of triclopyr formulated for diesel fuel. Care should be taken to avoid spraying surrounding vegetation with this mix, as diesel fuel is quite toxic to most plants (Heidorn 1991).

The herbicide 2,4-D has been used in Wisconsin with some success (sources in Converse 1984). A 4% ester (a.i.) in diesel fuel apparently provided good control when applied to the cut stump, or (alternatively) all the way around the trunk. Basal application of a 12.5 % a.i. Solution in diesel fuel, during the first half of the growing season, provided 100% control.

Foliar spraying: Foliar spraying is apparently not recommended to control buckthorns, probably because it is less effective and practical, and also more expensive than stump or bark treatments. The shoots produced after cutting are probably more susceptible to foliar spraying, because of their greater absorption and and closer proximity to the roots (Converse 1984).

Cultural Control

For use on medium to large stands.

Fire: Heidorn (1991) considers fire the best method for controlling common (and glossy) buckthorn in fire-adapted communities. Buckthorn seedlings are highly susceptible to fire, and under good conditions spring burning will mostly eliminate them. It can also remove the stems of larger plants. Established plants will resprout vigorously, though, so while some control will be evident after the first year, burning must be repeated every year (or at least every other year) for five years or more for good control. Unfortunately large, established patches of buckthorn prevent undergrowth of other species that would provide fuel, and so resist fire. One way around this is to cut the branches and leave them on-site, to provide fuel for future burns.

Flooding: For infestations of glossy buckthorn in wetlands, particularly wetlands that have been partly drained, Heidorn (1991) raises the possibility of restoring water levels to control it. Prolonged flooding will kill both glossy and common buckthorn. While common buckthorn is usually infrequent in wetlands, flooding may be an option for controlling this species in certain circumstances. Care must be taken to not raise water levels abnormally high, or more harm than good may be done to the native wetland plants and animals.

Biological Control

Despite the rapid spread of common and glossy buckthorn into natural habitats in North America, and the fact that common buckthorn is the alternate host for a major crop disease (oat crown stem rust), attempts to finds a biological control for these two invasive shrubs have until recently been minimal. In 2002, however, Minnesota Department of Natural Resources mercifully initiated a study to see whether biological control of these two buckthorn species in North America would be feasible (Skinner and Rendall 2002). This research is being conducted by the Center for Applied Bioscience International in Switzerland (CABI). To date, about a dozen species of insects have shown promise as control agents. Raising test plant species (including the native buckthorn species described previously) and testing these insects for host specificity and potential effectiveness in controlling Eurasian buckthorns may take as long as 10 more years.

Godwin (1943a) provides a list of insects associated with common and glossy buckthorn in Europe.

For More Information

TNC Wildland Weed Management and Research Library