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Controlling Non-Native Invasive Plants in Ohio Forests: Amur Corktree (Phellodendron amurense)

F-0108
Agriculture and Natural Resources
Date: 
01/21/2025
Jim Downs, Assistant Professor and Forestry Field Specialist, Ohio State University Extension
Carrie Brown, Educator, Agriculture and Natural Resources, Ohio State University Extension

Amur corktree (Phellodendron amurense) is native to China, Korea, and Japan. It commonly grows in the moist soils along the Amur River located between eastern Russia and northern China. It was introduced in the United States around 1865 as an ornamental. Within recent years the popularity of this tree as an ornamental has decreased due to its invasive nature.

Overhead view of two leaves with dark green leaflets growing in an equal arrangement along its length, with one leaflet growing from the tip of the rachis.The species is dioecious, meaning male and female flowers are produced on separate plants. The minimum seed-bearing age ranges from 7 to 13 years (Read & Zasada, 2008). Mature trees may annually produce seeds that ripen during September and October. Currently, no studies have determined the longevity of its seeds within the soil. However, the hard seed is consistent with other species that can remain viable in the seedbank for at least several years. These seeds are commonly spread by birds and wind. The tree is best described as shade intolerant, meaning that it grows best in areas with full sunlight. However, as a seedling it can tolerate growing in the understory of a closed canopy forest (Rohling, 2017). While Amur corktree prefers moist soils, it is highly adaptable to various soil conditions and can grow in disturbed woodlots, forest edges and openings, and unmanaged urban areas. Furthermore, it can benefit from its allelopathic properties that negatively impact the growth of neighboring vegetation (Weikert, 2024).View of yellow leaves with clusters of round green-black fruit growing from a section of a tree.

As of 2024, this tree is not listed as an invasive plant banned from commercial sale by the Ohio Department of Agriculture (Ohio Administrative Code, Rule 901:5-30-01, Invasive Plant Species, 2023). However, based on the Ohio Invasive Plant Council’s plant assessment protocol, Amur corktree possesses traits that identify it as invasive. Its potential for further spread is very high (Ohio Invasive Plants Council, 2022). Numerous other states within the region have identified Amur corktree as an invasive species, including Illinois and Pennsylvania, therefore we do not recommend planting this species. Some states, such as Minnesota, permit sales of only male cultivars (Minnesota Department of Agriculture, 2024). Current problem areas within Ohio seem to be concentrated in woodlands near landscapes where the tree was ornamentally planted. Within these areas, it has shown the ability to outcompete native vegetation.Close-up fingers holding the end of a stem with small buds on its end and a leaf scar nearly encircling a bud below.

Identification

Amur corktree is a small-to-medium-sized deciduous tree reaching heights of 50 feet, with crown widths nearly as wide when exposed to full sunlight. At maturity, the tree has a flattened-to-dome-shaped top. Within woodlands, the tree canopies are narrowed by competition for sunlight.

Shown in Figure 1, the tree produces opposite-arranged, pinnately compound leaves with seven to 13 ovate-elliptical leaflets. The leaf’s upper surface tends to be darker than its paler underside. The foliage turns bright yellow in the fall (Figure 2).

The growth and loss of its foliage occur at nearly the same time as many of our native trees, and therefore it does not receive an extra advantage regarding a longer growing season.View of side of tree trunk with section of its bark removed, showing bright-yellow inner bark.

The twigs are shiny brown, stout and contain numerous lighter-colored lenticels. The leaves and new-growth twigs provide a distinctive skunky or turpentine-like odor. The leaf scars are U-shaped and nearly encircle the fuzzy brown pointed bud (Figure 3). The twigs lack a true terminal bud (bud at the ending tip of the twig) but do grow paired buds near the end of the twig (Figure 3). The inner bark of the twigs and main stems have a distinctive bright-yellow color (Figure 4). The outer bark thickens with age and is quite furrowed with corky ridges that are dark tan to light gray (Figure 5). The flowers are produced in late spring to early summer and are upright with 2–3-inch, yellow-green clusters. The fruit are round, ¼–3/8 inch in diameter, single-seeded drupes that are dark blue to black when ripening in early autumn (Figure 2). This fruit may persist on the tree throughout the winter months.

Control Methods

When attempting to control Amur corktree, multiple control tactics may be considered. These tactics vary based upon time of year, size of plants, size of infestation, and the comfort level of the applicator with the control tactic. As with all invasive species management, a plan should be made to evaluate the effectiveness of the treatment to determine if additional control measures are needed.View of side of tree that has deeply furrowed bark.

Mechanical Control

Hand-pulling Amur corktree seedlings (usually less than 2 feet tall) can be a practical control option. This is best conducted when the soil is moist, as it is easier to remove the entire root system along with the upper stem. Hand-pulling is ineffective if portions of the root system remain in the soil. Cutting of seedlings or saplings is best conducted in early summer, when root reserves are at their lowest. Multiple rounds of cutting over several years will likely be necessary to achieve control, as this species will readily resprout especially if the plant is growing within a sunny area. The control of larger stems through cutting is generally not advisable due to the prolific resprouting that will occur. An effective strategy for controlling larger stems requires herbicide applications.

Foliar Spraying

Overhead view of leaf with wet, dark-green leaflets growing in an equal arrangement along its length, with one leaflet growing from the tip of the rachis.Uniformly spraying the leaves, but not to the point of runoff, with a dilute solution of herbicide can be an effective treatment method for Amur corktree seedlings (Figure 6). Care should be taken to avoid over-spraying or applying herbicide that results in runoff to avoid damage to non-target species. Foliar application may be effective any time after full development of the leaves in the spring until the leaves begin to turn color in the fall. Foliar spraying tall specimens (above the head of the applicator) should be avoided for the safety of the applicator. This strategy also helps avoid overspray which may damage nontarget species, and ensures consistent, adequate coverage of the spray across the foliage. Saplings taller than the applicator may be cut down. The resprouting vegetation may then be treated with a foliar application. Table 1 provides a detailed description of foliar herbicide options. In streamside areas or other wet areas, an herbicide labeled for aquatic use is necessary.Side view of tree trunk with bluish coloring on the tree’s bark from the ground up to approximately 18 inches from the base of the tree.

Basal Bark Application

This control tactic involves spraying the lower 10–18 inches of the uncut stem with an herbicide and oil-based carrier (Figure 7). A number of common oil-based carriers are available:

  • diesel
  • kerosene
  • fuel oil
  • methylated seed oil

The lower portions of the stem should be completely covered but not to the point of runoff. The bark of large Amur corktree stems can be thick, and the treatment of stems greater than 6 inches in diameter may prove unsuccessful. Care should be taken to avoid over-spraying, as improper applications can lead to negative effects to nontarget plants. An ideal time of year for this application is from late spring to early fall, though this treatment method may be conducted any time of year if the ground is dry and not frozen. Table 2 provides a detailed description of basal bark herbicide options.View of tree stump with bluish coloration along the bare wood on the top of the stump and bark surface from the top of the cut stump down to the ground.

Cut-Stump Application

This method involves cutting the tree’s trunk close to the ground and applying an herbicide to the cut surface and sometimes the bark. This is an effective treatment method for medium to large trees— especially trees too large to be effectively treated with a basal bark application. Either water-based or oil-based herbicides can be utilized for this treatment; however, their application techniques are different. When applying a water-based herbicide, only the outer cambium layer and sapwood should be treated. To be effective, this water-based application must be conducted within a few minutes of cutting the trunk. Oil-based applications are not nearly as time sensitive. These oil-based applications should be completed prior to the stump resprouting. A proper treatment technique for an oil-based herbicide is treating the sapwood, cambium, and outer bark surface down to the ground level (Figure 8). These applications can be made any time of year if the stumps are dry and not frozen; however, control is often most effective from late spring through early fall. Table 3 provides a detailed description of cut-stump application herbicide options.Overhead view down the length of a tree trunk, showing a deep, downward cut in the bark where a blue dyed herbicide was applied.

Hack-and-Squirt Application

This method involves applying an herbicide into the main stem of the tree through evenly spaced, downward-angled cuts using an ax or hatchet (Figure 9). The number of cuts needed will be based upon the size of the stem and the herbicide applied. Care should be taken to leave uncut living tissue between the cuts, as this allows the herbicide to move to the roots (Jackson, 2019). The ideal time of year for this application is from July through mid-October. Because the herbicide is applied to only a small area, this method minimizes the potential for nontarget effects. However, nontarget vegetation may be impacted if they are connected to the treated plant through underground root grafts. Table 4 provides a detailed description of hack-and-squirt application herbicide options.

Summary

As Amur corktree is not yet widely established throughout the state, an early detection and rapid response strategy may be used to control its spread. This is a coordinated set of actions designed to find and eradicate new and emerging invasive species. Early interventions are likely to be more successful and typically have a lower cost associated with them compared to the long-term management of well-established invasive species. For assistance with identification or control methods, contact an Extension educator, professional forester, or other qualified natural resources person.

Herbicide labels must be followed. Not only are labels the law, but following the label also maximizes the potential for successful control. Remember that new Amur corktree may enter the woodland from existing dormant seeds within the seedbank, wind, or songbirds. Additionally, in managed areas, treated stems may resprout. A plan for monitoring treated areas should be followed for at least two years to achieve complete control.

Herbicides, like all pesticides, are approved (labeled) for specific uses by the Environmental Protection Agency (EPA). Approved locations, uses, and application methods are listed and described on the pesticide labeling. The herbicides listed in this fact sheet were appropriately labeled at the time of publication. Because pesticide labeling may change at any time, always verify that a particular herbicide is still labeled for your intended use. At the time of this writing, copies of most herbicide labels and safety data sheets could be obtained online at the crop data management system website (cdms.net). Other labels are available through the individual manufacturer’s website. Ohio State University Extension does not endorse any of the products mentioned and assumes no liability resulting from the implementation of these recommendations.

Table 1 (click to download PDF). Herbicide recommended for foliar treatment to Amur corktree. Apply solution of herbicide in water as directed on label. Apply when leaves are green and actively growing.

Table displaying recommended herbicide foliar treatment for Amur corktree.

Table 2 (click to download PDF). Herbicide recommended for basal spraying to Amur corktree.

Table displaying recommended herbicide for foliar spraying to Amur corktree.

Table 3 (click to download PDF). Herbicide recommended for cut stump treatment to Amur corktree.
Table displaying recommended herbicide for cut stump treatment to Amur corktree.

 

Table 4 (click to download PDF). Herbicide recommended for hack and squirt treatment to Amur corktree.
Table displaying recommended herbicide for hack-and-squirt treatment to Amur corktree.

References

Jackson, D. R. (2019). Using hack-and-squirt herbicide applications to control unwanted trees [Fact sheet]. Penn State Extension.
extension.psu.edu/using-hack-and-squirt-herbicide-applications-to-control-unwanted-trees

Minnesota Department of Agriculture. (n.d.). Amur corktree.
mda.state.mn.us/amur-corktree

Ohio Administrative Code, Rule 901:5-30-01, Invasive Plant Species. (2023). Ohio Legislative Service Commission.
codes.ohio.gov/ohio-administrative-code/rule-901:5-30-01

Ohio Invasive Plants Council. (2022). OIPC plant assessment results.
oipc.info/uploads/5/8/6/5/58652481/oipcplantlist-educational2022.pdf

Read, R. A., & Zasada, J. C. (2008). The Woody Plant Seed Manual. In Phellodendron amurense Rupr, Amur corktree (pp. 783–785). USDA Forest Service Agricultural Handbook 727.
fs.usda.gov/rm/pubs_series/wo/wo_ah727.pdf

Rohling, K. (2017). Ecology and control of Amur corktree [Fact sheet]. University of Illinois Extension.
bugwoodcloud.org/mura/rtrcwma/assets/File/Fact_Sheets/Corktree%20Fact%20Sheet%20RTRCWMA%202017.pdf

Weikert, S. (2024). The invasive Amur corktree [Fact sheet]. Penn State Extension.
extension.psu.edu/the-invasive-amur-corktree

Originally posted Jan 21, 2025.
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