Managing Invasive Buckthorn in Natural Areas

 By CELESTINE DUNCAN,  Editor

By CELESTINE DUNCAN, Editor

Common (European) buckthorn (Rhamnus cathartica) and glossy buckthorn (Frangula alnus [Rhamnus frangula]) are non-native, deciduous, woody shrubs or small trees introduced to North America during the 1800s as ornamentals, hedgerow plantings, shelterbelts, and wildlife habitat. They escaped cultivation and have aggressively invaded natural areas and forestland throughout much of the United States and Canada (Figure 1). Non-native buckthorn spreads through intentional plantings and through wildlife seed distribution, especially from birds.

Listed as invasive, common and glossy buckthorn are restricted or prohibited noxious weeds in Connecticut, Massachusetts, Minnesota, New Hampshire, and Vermont. Common buckthorn is also listed as a primary noxious weed in Iowa (USDA, NRCS).

Identification and Distribution

Common and glossy buckthorn are deciduous shrubs or small trees that grow to about 25 feet in height. Common buckthorn has oval, dark-green leaves with finely-toothed margins. Small branches may be tipped with sharp spines. Glossy buckthorn can be distinguished from common buckthorn by the lack of thorns at the end of twigs and glossy or shiny leaves that lack toothed margins. Plants of both species reach seed-bearing age quickly, and both produce dark-purple to black drupes (berries). They reproduce by seed, but can also regrow from root crown sprouts following top-kill from fire or physical/mechanical damage.

Invasive buckthorn shares similar distribution and habitat with the native alderleaf buckthorn (Figure 1). Care should be taken not to mistake the native alderleaf buckthorn for these non-natives. Click here to distinguish non-native buckthorn from native buckthorn.

 Figure 1: Distribution of  non-native  common buckthorn (left), glossy buckthorn (middle), and  native  alderleaf buckthorn (right) in the United States and Canada (USDA, NRCS and EddMapS)

Figure 1: Distribution of non-native common buckthorn (left), glossy buckthorn (middle), and native alderleaf buckthorn (right) in the United States and Canada (USDA, NRCS and EddMapS)

Impacts

Non-native buckthorn impact establishment and growth of native herbaceous plants, shrubs, and trees, alter soil micro-and macro-organisms, and affect leaf litter decomposition. Although birds consume invasive buckthorn fruits, and the shrubs provide nesting sites, similar native shrubs appear to provide more desirable habitat.

Common buckthorn is considered a poisonous plant. Ingestion of bark, leaves, and fruit cause nausea, stomach cramps, gastroenteritis, diarrhea, and irritation of the gastrointestinal tract. Consumption of common buckthorn in sufficient quantity causes poisoning in cattle and reduces milk quantity and quality and meat flavor. The plant is a host for two invasive crop pests, oat crown rust (Puccinea coronata) and the soybean aphid (Aphis glycines). Several references suggest that glossy buckthorn fruit and bark are mildly toxic when ingested.

Management

Common and glossy buckthorn are difficult to control. Selecting the appropriate herbicide and/or combining herbicides with digging, cutting, burning, and restoring desirable understory vegetation will improve management success.

Buckthorn Control with Herbicide

Optimum control of buckthorn is achieved with either high-volume foliar or low-volume basal applications with Garlon® 4 Ultra specialty herbicide. High-volume foliar applications are applied by mixing a 2.5 percent solution of Garlon 4 Ultra (2.5 gallons Garlon 4 Ultra in 100 gallons of water) + 1 quart surfactant (0.25 percent v/v) and spray to thoroughly wet all buckthorn leaves and stems. [1] For low-volume basal applications, mix a 25 percent solution of Garlon 4 Ultra with basal oil, and apply to the lower 12 to 15 inches of the stem, all the way around the bark (Table 1).

 Table 1:  Low-volume basal tank mix guide  for Garlon® 4 Ultra specialty herbicide plus oil-based carrier

Table 1: Low-volume basal tank mix guide for Garlon® 4 Ultra specialty herbicide plus oil-based carrier

Basal cut-stump treatments involve cutting six inches above the ground level followed by an application of 25 percent Garlon 4 Ultra with basal oil (Table 1). Apply the herbicide solution to sides of the stump, including the root collar area, and to the outer portion of the cut surface (cambium) until thoroughly wet, but not to the point of runoff. Avoid cutting followed by herbicide application during heavy sap flow, since this can interfere with penetration of oil-based basal mixes and decrease control.

[1] Herbicide applications to woody plants growing in or adjacent to standing water must follow state and federal permit requirements for aquatic environments. On these sites, high-volume foliar applications should be made with Vastlan® specialty herbicide at 1.5 quarts + 2 quarts DMA4 + 1 quart of aquatic-approved surfactant (0.25 percent v/v) with 100 gallons of water.

Physical Removal

Individual buckthorn plants or low-density infestations along trails and roads can be controlled by physically removing plants. Seedlings or small buckthorn may be hand-pulled or removed with a weed wrench. Digging or pulling creates disturbed soil that may be readily colonized by new seedlings. Planting desirable vegetation in areas where buckthorn is removed, followed by selective herbicide treatment or prescribed fire, can control buckthorn seedlings.

Fire

Fire alone, even when repeated annually, does not provide adequate control of either common or glossy buckthorn. Control with fire may be improved by seeding desirable native plants following fire, or when fire is used in conjunction with cutting or basal herbicide treatments.

Conclusion

Common and glossy buckthorn are difficult to control. The use of selective herbicides alone or in combination with other management methods is part of a long-term management program. Infested sites should be monitored on an annual basis and buckthorn resprouts and seedlings controlled. The amount of time and effort needed for control will decline over time, but buckthorn may reestablish without continued vigilance. Infested sites should be prioritized, so the highest quality habitats are treated first. Sites with newly invading buckthorn are less expensive to treat and control will likely be greater than on sites where plants have been established for long periods of time. Presence of desirable competitive vegetation may reduce buckthorn seedling establishment.


References:

Burch, Pat. Field Scientist, Dow AgroSciences

Common buckthorn and glossy buckthorn. Maine Natural Areas Program and University of Maine Cooperative Extension. Bulletin 2505. Online at https://extension.umaine.edu/publications/2505e/

EDDMapS. 2018. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Online at http://www.eddmaps.org/; last accessed June 19, 2018.

Gucker, Corey L. 2008. Frangula alnus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Online at https://www.fs.fed.us/database/feis/plants/shrub/fraaln/all.html [2018, June 22].

Pergams, Oliver R. W.; Norton, James E. 2006. Treating a single stem can kill the whole shrub: a scientific assessment of buckthorn control methods. Natural Areas Journal. 26(3): 300-309.

USDA, NRCS. 2018. The PLANTS Database (http://plants.usda.gov, 21 June 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Zouhar, Kris. 2011. Rhamnus cathartica, R. davurica. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Online at https://www.fs.fed.us/database/feis/plants/shrub/rhaspp/all.html [2018, June 22].


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