What’s the best way to control invasive Chinese privet (Ligustrum sinense Lour) in a rural lawn? A year-long study recently conducted by the University of North Texas in a mixed-plant rural lawn infested with Chinese privet in north-central Texas sought an answer to this environmental issue. The objective was to compare the effectiveness of mechanical removal and chemical treatment of Chinese privet seedlings.
As landscapers may know, Chinese privet has invaded vast areas of the forested southeastern U.S. and is the most prevalent invasive shrub in eastern Texas. Its seeds even persist in digestive tracts of birds and other animals, enabling rapid spread across long distances. Once established, Chinese privet grows rapidly, quickly taking up nutrients and producing seeds. It contributes to declines in biodiversity by outcompeting native plants and altering habitats used by native animals.
To date, efforts to control Chinese privet have largely involved cut stump herbicide treatments and foliar applications to shrubs in forests, though biological controls also show promise. However, few studies have been conducted on the scale of a residential rural lawn. Yet rural neighborhoods near impacted woods are also vulnerable to Chinese privet infestation. The objective of this study was to compare the effectiveness of mechanical removal and chemical treatment of Chinese privet seedlings in a rural lawn in north-central Texas.
A mixed-plant lawn was studied in a rural neighborhood at the northern edge of the Dallas/Fort Worth metropolitan area. The neighborhood comprises several lots, approximately one acre in size, and borders a lake, ephemeral creeks, and a wooded wildlife management area. Over the past few decades, Chinese privet has invaded wooded areas around and throughout the neighborhood.
The lawn is mowed at approximately two week intervals, from May through October, and infrequently in other months. Long, hot summers (growing season) and short, mild winters characterize the area. Annual precipitation and lake evaporation in this region average approximately 33″ and 52″, respectively. Typically, high rainfalls and seasonal flooding occur in the Spring, followed by occasional droughts in the Summer, though weather may vary widely outside of hot summer months.
The lawn was approximately 4″ tall at the start of the study. Notably, the mowing practice used at this lawn, somewhat typical of the neighborhood, does not prevent Chinese privet seedlings from establishing. As a result, numerous seedlings were available for study. Neither plot was mowed during the study; however, during the growing season, fast-growing plants were trimmed to just below 8″ in height.
Over the course of a year, two plots on the lawn were studied, each approximately 969 square feet in size. In the first plot, a notched hand spade was used in January to uproot 95 privet seedlings, exhuming the entire canopy and root structure. Predominant plants in this plot (listed in approximate order of abundance) included: Little bluestem, Rescuegrass, Carolina dichondra, Mouse-ear chickweed, Mallow, Dandelion, Buckhorn plaintain, Henbit, and Pale seed plaintain.
In the second plot seedlings were chemically treated by hand spraying with glyphosate solution. Predominant plants in this plot (listed in approximate order of abundance) included: Rescuegrass Bluestem, Henbit, Mouse-ear chickweed, Carolina dichondra, Dandelion, Sticktight buttercup, Ragweed, and Wild onion. A fourth, control category of 26 seedlings was not chemically treated.
Established a week later, the chemical plot had 104 seedlings, including 26 in each of four categories: (1) control, not sprayed; (2) sprayed with 1% glyphosate; (3) sprayed with 3% glyphosate; and (4) sprayed with 5% glyphosate. Plants were sprayed once, on January 26, 2019, with approximately .4 fluid ounces of fine mist, enough to saturate the exposed canopy and stem.
Plant survival was assessed periodically, and the study concluded at the end of January this year. For various observation dates, a one-way chi-square was used to evaluate differences in observed versus expected numbers of plants surviving among: (a) all four categories (control and three chemical treatments); and (b) the three treatments. Tests for significance used a probability (p) level of 0.01.
Results & Conclusion
None of the mechanically-removed plants returned, whereas the chemically-treated plants died off at varying times (Table 3). Initial mortality in sprayed plants was observed after 2.6 months. However, no significant difference in survivability among all four categories occurred until 4.3 months; at that time, fewer than half of the seedlings were alive in each of the sprayed treatments. Significant differences in survivability among all four categories persisted over the remainder of the study (Table 3). After 9.2 months until the end of the study, all sprayed plants died while 20 control plants survived. No significant difference in survivability was observed between the three sprayed categories during the study.
In conclusion, mechanical removal was completely effective, whereas chemical treatment showed mixed results in controlling Chinese privet seedlings in a rural lawn. Yet no significant differences were observed among sprayed categories during the study. Based on this study, mechanical removal may be more effective than one-time spraying, and 1% glyphosate sprays may be as effective as higher concentrations (up to 5%), for controlling Chinese privet in infrequently mowed, mixed-plant rural lawns.
Hudak is a professor with the Department of Geography and the Environment at the University of North Texas in Denton, TX.