Controlling Non-Native Invasive Plants in Ohio Forests: Privet (Ligustrum spp.)

Non-native and invasive privets compete aggressively with native plant species and degrade woodland quality and wildlife habitat. After privet becomes well-established, control requires substantial investment of manpower and resources. Early detection and rapid response are the most effective means of keeping these species under control. Early establishment of privets often occurs along roadsides, stream corridors, and trails. Subsequently, privets invade adjacent forests and fields. It is essential to regularly scout for and control these species, especially prior to and shortly after a harvest or other disturbance activity.

Privets are deciduous to semi-evergreen, multi-stemmed shrubs with spreading branches that project outward at near right angles (Figure 1). They were first introduced to the United States in the mid-1800s from China, Europe, and North Africa for use in landscaping (Fire Effects Information Center, n.d.). Since privets thrive in full sunlight and tolerate heavy shade, they are aggressive invaders of a variety of sites including disturbed areas, bottom-land forests, fencerows, fields, and rights-of-way. Dense thickets of privet can form and crowd out desirable native woodland species. Exotic privets leaf out early in the spring and retain their leaves through early winter, giving them a competitive advantage over native plants (Figure 2). Privets aggressively spread by seeds that are primarily transported by birds. Additionally, privets have the natural ability to produce roots where branches come into contact with the ground, a process referred to as layering. This provides privet with an additional means of spreading.

European (L. vulgare), Chinese (L. sinense), border (L. obtusifolium), and Japanese (L. japonicum) privets are considered a group in this fact sheet since they are difficult to distinguish from one another. These privets hybridize, grow in similar environments, and respond similarly to control techniques. As of 2025, European, or common, privet is the only privet banned from commercial sale by the Ohio Department of Agriculture (Invasive Plant Species Ohio Administrative Code 90:5-30, 2023).

Identification

Privets are multi-stemmed shrubs reaching heights up to 16 feet with stems that can grow as wide as 10 inches in diameter. Privet can be identified by the following characteristics:

• Leaves
  Small (0.8–1.6 inches) with smooth margins (without teeth), growing opposite and at near right angles to the stem (Figure 3). Shiny green above and pale green beneath. Chinese privet has a hairy mid-vein on the underside of the leaf while European privet leaves are hairless.
• Stems
  Arrangement is opposite. Bark is brownish-gray to gray and slightly rough with light dots (lenticels). Spurs (sharp-pointed branches) are often present (Figure 4). Twigs are gray-green in color and slightly hairy.
• Flowers
  Abundant, small, fragrant white flowers appear May to June. Arranged in clusters at or near the tips of branches.
• Fruits
  Form in late summer as clusters of pale green ovoid drupes at or near the branch tips. Ripened fruit is dark purple to nearly black in late fall and persists into winter (Figure 5). Fruit is mildly toxic to humans and should not be eaten. Most privet seeds germinate shortly after dispersion and therefore do not form long-lasting seed banks (Shelton & Cain, 2002).

Control Methods

When attempting to control privet, several methods may be considered. The method applied depends on the size of the plants, the size of the infestation, and a landowner's comfort level with the control method. For a more detailed description of the control methods recommended in this fact sheet, refer to the Ohio State University Extension fact sheet Controlling Undesirable Trees, Shrubs, and Vines in Your Woodland (ohioline.osu.edu/factsheet/f-45).

Mechanical Control

Infestations of small plants can be pulled, dug, or cut out. Pulling or digging out small plants is ineffective if all roots are not removed because the remaining portions of the root system can resprout. These treatments are most effective when the soil is moist. Cutting is most effective when underground food reserves are at their lowest in early summer. Plants should be cut as close to the ground as possible. Cutting must be repeated multiple times a year for several years to achieve control.

Mechanical control alone is usually not an effective method of controlling medium to large privet shrubs. Cutting the shrub off at the base will cause prolific sprouting and increase the number of stems. An effective strategy for controlling large privet shrubs targets the shrub and the root system to eliminate the potential for sprouting. This can be achieved using herbicides.

Foliar Spraying

Leaves of the targeted plant should be covered uniformly with a diluted herbicide, but not to the point of runoff (Table 1). Over-application of herbicides can result in unacceptable damage to non-targeted plants.

Privets stay green into early winter after most native plants have gone dormant. Foliar applications of non-residual herbicides (e.g., glyphosate products) can be used at this time with little to no impact on non-target species, especially after the first hard frost.

Foliar application of herbicides to tall shrubs should be avoided as it can increase the risk of herbicide exposure to non-target species from over-spray. To avoid exposure to herbicides on non-target species, control large privet shrubs by cutting them at the base and allowing the shrub to re-sprout or by choosing a different application method. The follow-up applications should occur when plants have grown new foliar tissue that is knee- to waist-high.

When treating privets in streamside areas or other wet habitats, it is necessary to use an herbicide labeled for aquatic use, such as Accord, Aquaneat, Rodeo, or Roundup Custom.

Basal Bark Application

Another control option for treating large privet shrubs is to apply an herbicide-and-oil mixture to the base of uncut privet stems (Table 2). Several oil-based carriers are available for use including diesel, kerosene, fuel oil, or methylated seed oil. For a basal herbicide application to be effective, the lower 10–18 inches of all stems in the clump must be completely covered, ensuring that the stems are wet—but not to the point of runoff. However, due to the dense nature of privet shrubs, it is often difficult to achieve complete coverage. Basal-bark treatments should only be applied when the areas to be treated are dry and not frozen. To avoid injury to non-target plants, care should be taken to avoid over-spray.

Cut-Stump Herbicide Treatment

Another effective method for controlling large, undesirable, woody shrubs is the cut-stump treatment. This method involves cutting the shrub off close to the ground and applying an herbicide to the cut surfaces (and sometimes the bark) with a spray bottle or paintbrush.

Water-carried and oil-carried herbicides can be used for cut-stump applications (Table 3). Herbicides carried in water should be applied to the outer ¹/₃ of the top of the stump within minutes of making the cut.

Oil-soluble herbicides are not as time-sensitive if applied before resprouting. These mixtures are applied to the entire top and sides of the cut stems but not to the point of runoff. Applications can be made any time of the year if the stumps are dry and not frozen. Control is usually most effective when applications are made late in the growing season. Dormant season applications have also proven to be effective.

Environmental Note

Many of the herbicides recommended for basal or cut-stump applications are labeled to be mixed with penetrating basal oil, diesel fuel, fuel oil (No. 1 or No. 2), or kerosene as their carrier agent. The choice to utilize non-petroleum basal oil (particularly methylated seed oil) instead of petroleum-based oils will result in a more environmentally friendly practice that does not expose the applicator to offensive petroleum fumes.

Summary and Disclaimer

To protect yourself, minimize harmful effects to the environment, and maximize the potential for successful control, read and closely follow all herbicide label instructions including recommendations for personal protective equipment (PPE), mixing, application equipment, and maximum per-acre rates allowed. Remember, the label is the law and any use of an herbicide inconsistent with the labeling is prohibited.

Follow-up treatments are often necessary to achieve satisfactory control of privet. Monitor treated sites for at least two years to determine if control is achieved. Often, shrubs resprout and new seedlings germinate which will necessitate follow-up treatments.

Herbicides, like all pesticides, are approved (labeled) for specific uses by the Environmental Protection Agency. Approved uses and application methods are listed and described in 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, you should 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). Others are available through the individual manufacturer's web sites. OSU Extension, the Ohio Division of Forestry, and the authors do not endorse any of the products mentioned and assume no liability resulting from the implementation of these recommendations.

References

Invasive Plant Species Ohio Administrative Code 90:5-30. (2023). Ohio Legislative Service Commission.
codes.ohio.gov/ohio-administrative-code/rule-901:5-30-01

Shelton, Michael G., & Cain, Michael D. (2002). Potential carry-over of seeds from 11 common shrub and vine competitors of loblolly and shortleaf pines. Canadian Journal of Forestry Research, 32, 412–419.

U.S. Department of Agriculture. (n.d.). Fire effects information system.
fs.usda.gov/database/feis/plants/shrub/ligspp/all.html#FIRE%20EFFECTS

Originally written Feb. 25, 2014, by Annemarie Smith, Invasive Species Forester, Ohio Department of Natural Resources, Division of Forestry; Eric Boyda, Coordinator, Appalachian Ohio Weed Control Partnership; and David Apsley, Natural Resources Specialist, Ohio State University Extension.

Reviewed on March 11, 2024, by Kathy Smith, Program Director, Forestry; College of Food, Agricultural, and Environmental Sciences; Ohio State University Extension