Invasive Species—Best Control Practices Michigan Department of Natural Resources Michigan Natural Features Inventory 2/2012 Glossy buckthorn Frangula alnus Glossy buckthorn is native to Eurasia but has been com- monly planted in this country as a hedge and for wildlife food and cover. It was widely recommended for conserva- tion plantings in the Midwest until its invasive tendencies became apparent; it creates dense thickets and out-com- petes native vegetation. Its fruit is widely dispersed by birds and small mammals. Glossy buckthorn, like many invasive shrubs, leafs out early in the spring and retains its leaves late into fall, increasing its energy production and shading out native plants. It is a particular pest on wet sites and poses a significant threat to Michigan’s rich prairie fens, as well as other wetland com- munities. It is also successful on many upland sites including old fields, roadsides and open woods. Glossy buckthorn is an alternate host for alfalfa mosaic virus and crown fungus, which causes oat rust disease. It has also been implicated as a possible host for the soybean aphid. It is widely distributed in some parts of the state, but is just beginning to appear in others. If it is caught early in its initial invasion, it may be eradicated completely. Robert Vidéki, Doronicum Kft., Bugwood.org Identification Flowers: Habit: Glossy buckthorn flowers Glossy buckthorn is a small tree or shrub with a spreading are tiny with five greenish- crown growing up to 6 m (20 ft) tall. Typically, it has multiple white petals, arranged in stems when young, and develops into a tree with a trunk clusters at the bases of the that may reach 25 cm (10 in) in diameter at maturity. leaves. The flowers contain both male and female parts. Leaves: They bloom from late May Glossy buckthorn has through September. Suzan Campbell, MNFI simple, shiny leaves, with 8 or 9 pairs of veins and Fruits/Seeds: untoothed margins. Leaves Buckthorn has pea-sized are alternate although they fruits with 3-4 seeds. They may appear almost opposite ripen from green to red Suzan Campbell, MNFI near the branch tips. to dark purple from July through September, al- Bark/Stems: though flowers, unripe and Glossy buckthorn stems are ripe fruit may all be present greenish, often with tiny, soft at the same time. Seeds are fine hairs. The bark on older Suzan Campbell, MNFI viable for several years. branches is a blotchy grayish- brown with prominent light Habitat raised areas. Winter buds lack Glossy buckthorn does best on sunny moist sites, although scales and are rust-colored. James H. Miller, USDA Forest it can tolerate shade. It is found in a variety of wetlands in- The sapwood, just below the Service, Bugwood.org cluding fens, as well as pastures, fence rows, roadsides, open outer bark, is yellow and the heartwood is pinkish to orange. woods including aspen stands and woodland edges. 1 Similar species eat and store glossy buckthorn fruit and seedlings sprout from their abandoned caches. Common buckthorn Fruit production is greatest on sites in full sun with moist The related common buck- soils. Plants in shadier conditions can persist without fruiting thorn (Rhamnus cathartica) for years until a gap in the canopy appears and they receive has finely toothed leaves enough sunlight to flower and fruit. and flowers with four petals rather than five. Often, it has Paul Wray, Iowa State Planning a control program a small thorn at the tip University, Bugwood.org of its branches, between the terminal buds, which are cov- Resources for invasive species control invariably fall short of ered by scales. It has 3 to 5 leaf veins rather than the 8 or 9 the actual need, so it is important to prioritize sites for treat- of glossy buckthorn. It is also invasive. ment and plan carefully. Assessing both the scope of the problem and any available resources is a critical first step: Alder-leaved buckthorn The native alder-leaved • Map known populations; is the species widely distrib- buckthorn (Rhamnus alnifolia) uted throughout the region? Just beginning to appear? is less than 1 m (3 ft) tall and • Does it occur on high value sites? Important hunting or has leaves with tiny rounded recreational lands? High quality natural areas? Sites with teeth and 6 or 7 pairs of high cultural value? veins. Its flowers lack petals • How is it distributed? Is it sparsely scattered in otherwise but have five sepals, rather native vegetation? Does it cover large expanses of low Bev Walters, than four. It grows in fens and quality habitat? University of Michigan other wetlands. • Is there the potential to utilize volunteers? Dogwoods Given this information, develop a strategy for control: Dogwoods (Cornus spp.) 1. Prioritize high value sites where success can be have opposite leaves rather achieved for treatment; than alternate and their fruit 2. Choose appropriate control methods, given site condi- and flowers are arranged in tions and available resources. clusters on reddish stems. 3. Do these control methods require any permits (i.e. her- The fruit is blue or white, bicide application in wetlands, prescribed burning)? rather than deep purplish Suzan Campbell, MNFI 4. Focus on mature plants, particularly those in full sun black. with abundant fruit; 5. Eradicate smaller satellite populations; Reproduction/Dispersal 6. Treat larger core infestations of lower value as Glossy buckthorn reproduction is primarily by seed. Buck- resources permit. thorn is insect pollinated and cannot self-fertilize. Plants 7. Monitor to ensure desired results are being achieved; mature quickly and can produce fruit at heights of less than adapt management to improve success. 1 m (~3 ft) tall. They can also sprout from the root crown when cut. Plants that have been top-killed can produce fruit Best survey period on new shoots within the same season. Because glossy buckthorn leafs out early and retains its leaves late in fall in much of the state, it is often easiest to Although many glossy buckthorn seedlings appear under locate for mapping or control efforts in early spring or late their parent plants, germination and seedling survival rates fall when the leaves of native vegetation are absent or have are highest in full sun on exposed soils. Glossy buckthorn of- changed color. It is also easier to distinguish from its neigh- ten establishes in open fields, in the sunny edge along paths bors when in fruit. and roads and along the forest edge. Following removal of mature shrubs, abundant seedlings rapidly germinate and Documenting occurrences must be considered when formulating control strategies. In order to track the spread of an invasive species on a Birds are a major dispersal agent for glossy buckthorn. Rob- landscape scale, it is important to report populations where ins, cedar waxwings, rose-breasted grosbeaks and starlings they occur. The Midwest Invasive Species Information Net- have been observed feeding on their abundant fruits. The work (MISIN) has an easy-to-use interactive online mapping unripe fruit contains the chemical emodin, which has a system. It accepts reports of invasive species’ locations from laxative effect, facilitating its spread. Small mammals also users who have completed a simple, online training module disperse glossy buckthorn seed, particularly rodents. Mice for the species being reported. It also offers the potential for 2 batch uploading of occurrence data for any invasive species. its leaves. When it is cut, the tree slowly begins to die. Herbaria also provide a valuable and authoritative record of Use an axe or saw to make two parallel horizontal cuts plant distribution. The University of Michigan Herbarium’s around the trunk several inches apart, cutting through the database can be searched online for county records of bark and cambium. Then, knock off the bark between the occurrence, for example. When glossy buckthorn is first cuts. The tree should be checked periodically for two years encountered in a county where it had not been known pre- to cut off any resprouts and to ensure that the bark does not viously, specimens should be submitted to the Herbarium heal over. Girdling is more effective when used in conjunc- to document its presence. Check the “Online Resources” tion with herbicide. section for links to both of these resources. Flooding Control On wetland sites where water levels have been lowered artificially, restoring the hydrology may kill or set back A primary goal in controlling this species is to prevent seed glossy buckthorn. An extended period of flooding during production and dispersal. Glossy buckthorn is one of the the growing season is required. The duration and timing most difficult invasive shrubs to control. A variety of tech- of flooding is as important as water depth. This is perhaps niques including both mechanical and chemical controls most appropriate where restoring hydrology is part of a may be most effective and should be tailored to the specific larger management program and should be used in con- conditions on the site. It is critical to monitor the site to junction with other control methods as needed. It is impor- ensure that cut stumps and treated shrubs do not resprout tant not to raise water levels higher than they were histori- and that the seedbank is exhausted. Removal of a dense cally, to avoid harming sensitive native vegetation. glossy buckthorn thicket “overstory” results in dense seed- ling response. Where abundant seed sources are present Chemical control nearby, monitoring may be required indefinitely. In most cases, effective control of glossy buckthorn requires Mechanical control the use of herbicide. Factors that should be considered when selecting an herbicide for use on a particular site in- In the very earliest stages of invasion, when only scat- clude proximity to water or wetlands, presence or absence tered seedlings and young plants are present, mechanical of desirable native vegetation, potential for erosion and the controls such as pulling and digging may be adequate to effectiveness of the herbicide under consideration on glossy control or eradicate glossy buckthorn.