June 09, 2023
In Part 1 of this series, I discussed the first of what I refer to as the “Dirty Four” of invasive plants, as they relate to the White-tailed Deer — Kudzu. We now turn to the second in the group, Chinese Privet.
My first exposure to Chinese Privet (Ligustrum sinense) was as a boy, when my father planted a hedge of it to separate our yard from our neighbors. The plants were only about a foot tall when we planted them, but within three years, they were over six feet tall! One of my duties was to keep them trimmed to that height, which became a constant battle throughout the long growing season of Central Texas! Long before becoming a professional wildlife biologist, I had a profound respect for the hardiness of privet.
Privet first arrived in the U.S. in 1852, after which it quickly was adopted as a “go to” landscape hedge. Its growth characteristics are well-suited as a hedge and border plant, in that it is semi-deciduous; meaning that it never really drops its leaves. It also grows quickly, requiring frequent trimming to keep it within the desired height.
Another trait beneficial to gardening is that it is broadly adapted to soils and sites, ranging from dry uplands to wet bottomlands. In the 170 years since introduction, privet has spread across the South and into New England (see range map). The USDA lists privet as being suitable for Hardiness Zones 6a to 17. I can personally attest to its ability to withstand very cold temperatures, since we have it growing all over the Institute for White-tailed Deer Management and Research here in Nacogdoches, Texas, and it easily survived the -12 degrees Fahrenheit temperatures from 2021’s “Snowmagedden!”
Yet, does this species have any beneficial impact on white-tailed deer?
Chinese Privet has a bi-polar personality when it comes to its potential impact on the deer woods. The first “personality” is that it provides nutritious browse to whitetails, with data reported by the University of Georgia (D. B. Warnell School of Forest Resources) showing rumen volume of foliage and berries during 1992-94 of 11.1 percent in fall and 13.3 percent in winter.
During this study, crude protein was about 12 percent, suggesting it is a second choice browse plant — the mainstay of whitetails. Privet berries also are relished by many songbird species, giving rise to one of the ways privet is spread. Droppings from birds along powerlines and edges contain viable seed that quickly spread the plants across the landscape.
So, there is no doubt Chinese privet can be beneficial to wildlife! So, you may ask, what is so bad about this species?
The second personality of privet is related to its prolific reproductive capacity and rapid growth habit. We have been fighting this species at the Research Institute for over 40 years and have not begun to win! Not only have birds spread privet across our deer woods, but it also has another insidious method of reproduction — vegetative spread.
Once established, the plants send out “suckers” that show up feet from the mother plant, and quickly grow into new shrubs. The incredible fast growth rate has a significantly negative impact on our native browse and forbaceous species; they simply cannot compete in growth rate. Understory plants are limited by shade, coming both from the overstory trees and midstory shrubs and young trees.
Wildlife biologists learned long ago that, to produce deer food, you must get sunlight to the ground. We thin forests to encourage understory growth by reducing the canopy closure. We then conduct prescribed burns to maintain them at a desirable height within the deer zone. Privet loves both cultural practices, becoming even more aggressive against native plants.
So, given the bipolar personality of Chinese privet, where does it fit into a deer management program across the landscape of its adopted land? Frankly, it is one of those species I honestly believe we never will control; yet we certainly can manage it! Here at the Institute, we long ago tested ways to at least keep privet within some context of ecological management. First, we studied ways to kill the plants, since burning did not accomplish this task. Only two techniques have shown any promise — mechanical removal and herbicides.
Chinese privet has a very extensive root system, which tends to grow way beyond the stem of the plant. Pulling up the plants certainly worked in getting rid of specific plants, but as South Texas ranch managers quickly learned about mesquite control, the roots left behind quickly produce new plants! Bulldozing certainly reduced the number of new plants, but only for a short time. That brought us to the use of herbicides. The problem, however, is there are no herbicides available that kill only privet. We feel Trichlopyr is the most useful herbicide for wildlife management in the forest (often sold under the trade names Remedy, Garlon and Access).
Triclopyr is a commonly used herbicide developed in 1979, that is designed to kill woody and broadleaf plants. It has been used extensively in forest management applications, but also found a home among range managers, since grasses are less sensitive to the active ingredient. There are some 200 products currently available containing Triclopyr, provided as liquid, granules, or powders. Oil or diesel often are used as a carrier, especially for basal or foliar applications. The chemical mimics a growth hormone of plants, which essentially makes the plant “grow itself to death!” It is classified as non-toxic to slightly toxic to birds, bees and shellfish. It is applied directly to the plant, and is not considered soil active, and it is quickly degraded by soil microbes.
We use either a basal application of Triclopyr and diesel (or mineral oil), which requires individual plant treatment. This takes a great deal of time, so we limit basal application to large plants, and foliar spray to smaller plants. The advantage of triclopyr is that you can limit use to specific plants, without damaging native plants in and around the privet plant itself. We do not recommend broadscale application by spraying since there is a significant negative impact on the native plant community.
Over time, we also have learned that, if we use a 2-4 year prescribed burn rotation, we can keep privet fairly low in the understory vegetation, giving other plants the opportunity to thrive. This provides browse, while controlling the spread of the plants. Our experience under the forest canopy is that the burn rotation we are using does not allow the plants to flower and fruit. We only do this in about 20 percent of areas managed for deer forages; in the remainder we tend to wage war on privet whenever possible.
The greatest problem is that our neighbors do absolutely nothing to control privet; and, since birds spread the seeds, managing Chinese privet is a constant battle. Chinese privet is a constant reminder that we ought not introduce new plant species, without first being fully educated about the potential for becoming yet another addition to the long list of invasive species.