Common Buckthorn Control
Common buckthorn ia a shrub or small tree reaches heights of 25 feet (7.6 meters); trunk diameter is up to 10 inches (25 cm); crown is spreading and irregular. The bark is gray to brown, showing a rough texture when mature. Twigs are often tipped with a spine. Leaves and bud scars are nearly opposite to opposite. Small black fruits up to 1/4 uarter inch (0.6 cm) diameter and containing three or four seeds are typical. Leaves are broadly elliptic, rounded to pointed at the tip, and toothed. Both upper and lower leaf surfaces are smooth. Leaves stay green late into fall.
Two native species of buckthorn are found in Missouri. These are Carolina buckthorn (Rhamnus caroliniana) and lance-leaved buckthorn (Rhamnus lanceolata). Carolina buckthorn is essentially restricted to the Ozark region in Missouri, whereas lance-leaved buckthorn is found throughout the state with the exception of the Mississippi Lowlands of southeast Missouri. Both species grow in soils derived from limestone or dolomite. Common buckthorn can be distinguished from both native species by its opposite or near opposite leaf arrangement and by the presence of spiny tips on its twigs. Its leaves are abruptly pointed to rounded at the tip, whereas the two native species both have leaves that are more gradually tapered to a point at the tip.
Common buckthorn should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.
This exotic buckthorn is an endemic of Eurasia that was introduced to North America as an ornamental shrub. It has become naturalized from Nova Scotia to Saskatchewan, south to Missouri and east to Virginia. Distribution records from Missouri are scattered, but the species probably has the potential for establishment throughout the state.
Common buckthorn inhabits woodlands and savanna. It is quite sun tolerant, as it is also found in prairies and abandoned fields. It is cultivated for hedges and wildlife habitat and is used in shelterbelt plantings. It has become naturalized in pastures, fence rows, roadsides and slopes of ravines.
Common buckthorn produces fruit that is readily eaten by birds. The severe laxative effect of the fruits readily distributes seeds. The shrub readily re-sprouts from cut or damaged stems.
Effects Upon Natural Areas
Common buckthorn readily invades natural communities. Once established, it crowds or shades out native shrubs and herbs. It can invade woodlands, savannas and prairies.
Exotic buckthorns are sold as ornamentals by several nurseries and are used as hedges in many urban areas. There are no current legal restrictions on the sale or propagation of these plants.
Recommended Practices in Natural Communities of High Quality
As with all management, control efforts must balance improvement of the biotic community with damage caused by the management. It is always best to take the least damaging approach that will affect the desired control of an exotic. The following are effective control measures for common buckthorn.
Fire is sometime effective in controlling buckthorn. Regular prescribed fire will kill seedlings and stems of this species in fire-adapted upland sites, although re-sprouting may occur. Some control usually will be evident after the first burn. However, for complete control in established stands of buckthorn, burning yearly or every other year may be required for five to six years or more. Early spring burns, late April to early May, capitalize on the fact that buckthorn leafs out earlier than most native shrubs. Burning shortly after leaf out may reduce re-sprouting, since root reserves will be low at that time. Fire should not be used to control this species if the community will be affected adversely. Burns should be conducted by 37 persons trained or experienced in conducting prescribed burns, and proper safety precautions should be followed.
When burning is not feasible, larger trees can be cut or girdled and re-sprouts clipped as they occur. When using chainsaws and other power equipment, proper safety equipment and precautions need to be used. For safety recommendations refer to your chainsaw owner's manual. For girdling to be effective, use an ax or saw to make two parallel cuts 4 to 5 inches apart, cutting through the bark slightly deeper than the cambium. The bark is then either knocked off, using a blunt object like an ax head, or peeled away, using a blunt ax blade. Phloem should be removed without damaging the xylem. Girdles should be checked after a few weeks to make sure that bark does not develop over the cut area. Girdled trees take time to die and the results may not be seen until a year later. Basically, the tree is slowly starving to death. All suckers should be cut. Since girdling will probably produce abundant sprouting below the girdle, the cut-stump treatment described below will provide a more efficient means of control by eliminating sprouting.
In upland areas where burning is not feasible, cut stumps can be treated with Trimec (a formulation of 2,4-D, MCCP and Dicamba) or Roundup (formulation of glyphosate) to prevent re-sprouting. Trimec, an herbicide specific for broadleaf plants, should be diluted with an equal portion of water and applied according to label instructions. Roundup is non-specific and kills all photosynthetically active vegetation. Although the Roundup label recommends a rate of 50 to 100 percent for cut-stump treatment, a 50-percent solution has proven effective. Autumn is the preferred time to cut and stump-treat buckthorn, because 1) buckthorns retain green leaves late into the fall, making it easy to find all plants and 2) most native vegetation is dormant, minimizing the potential harm to non-target plants.
To be effective, the herbicides mentioned above must be applied immediately after cutting. Consult appropriate herbicide label(s) for specific application directions. These chemicals can be applied either by spraying individual cut stumps with a low pressure hand sprayer or else by wiping the herbicide on each cut stump with a sponge applicator (sponge-type paint applicators can be used). Care should be taken to avoid herbicide contact with non-target plants. Native non-target plants will be important in recolonizing the site after buckthorn is eliminated. By law, herbicides may only be applied according to label directions.
Recommended Practices on Lands Other Than High-Quality Natural Areas
Same as given above for high-quality areas, with the following additions:
In addition to the cut-stump treatments recommended above, Garlon 3A (a formulation of triclopyr) is a selective, translocated herbicide that can also be applied on cut stumps. A 50-percent Garlon solution diluted with water can be sprayed, using a hand sprayer, to the cut stump. Application should be within minutes of cutting. Cut-surface application can be made during any season of the year, but application during the dormant season reduces the potential for drift injury.
Dormant season basal-bark treatment using Garlon 4 herbicide is effective on trees and re-sprouts less than 6 inches in diameter, however, this treatment is not labeled for use in wetlands. Two to two and one-half oz. of Garlon 4 is added to one gallon of diesel fuel. Spray this mixture, using a hand sprayer, to the basal portion of the trunk. Spray to a height of 12 to 15 inches (30.5-38.1 cm). A thorough spraying is necessary. This treatment should not be used in high quality natural areas because the diesel fuel may kill vegetation around the tree.
Another formulation using Garlon 4 has been used successfully in the spring and fall at Cuivre River State Park in Lincoln County, Missouri. Managers there used a mixture of Garlon 4 (25 percent), Cide-kick (10 percent), and diesel fuel (65 percent) as a thin-line treatment for common buckthorn. Cide-kick is a spreading agent that improves the ability of a spray to encircle a stem when sprayed from one side. If the treatment is done during the dormant season, the percentage of Garlon 4 may be increased to 30 percent. Stems under two inches in diameter were sprayed on only one side. Larger stems were sprayed all the way around. All but the larger trees were killed completely using this method. Fall treatment was preferred because of the ease of spotting buckthorn after most other vegetation had lost its leaves.
Use of Garlon 4 is best done in the dormant season to lessen damage to non-target species. Great care should be exercised to avoid getting any of the mixtures on the ground near the target plant since some non-target species may be harmed. Avoid using Garlon 4 if rain is forecast for the following one to four days, otherwise runoff will harm non-target species. In areas of heavy infestation, a large seed bank of common buckthorn in the soil will probably necessitate repeated control measures for a period of years, as new seedlings emerge. Seedlings or small plants may be hand pulled or removed with a grubbing hoe or larger plants may be pulled out with heavy equipment. Excavation often disturbs roots of adjacent plants, or creates open soil that may be readily colonized by new seedlings. This technique may be most useful to control invasion at low densities, or along trails, roads and woodland edges.
Failed or Ineffective Practices
No effective biological controls that are feasible in natural areas are known.
Girdling or cutting without chemically treating the stumps will cause sprouting that will require re-treatment by cutting or using foliar sprays.