This is an impressive 2018 study on treating Chinese privet (Ligustrum sinense) with herbicide: Enloe et al., The Influence of Treatment Timing and Shrub Size on Chinese Privet (Ligustrum sinense) Control with Cut Stump Herbicide Treatments in the Southeastern United States. Note also that the study has good advice for treating many different kinds of woody invasives that are prone to lateral sprouting – tree of heaven being another prominent one. Here’s specifically what I like about the research they conducted.
First, the researchers used good technique for doing cut stump treatments. They cut the stump low to the ground – about 1 inch above ground level. Anecdotally, I have found that cutting the stump low to the ground makes a difference in the success of the treatment.
The researchers applied the herbicide immediately after making the cut – within 30 seconds. It is not known how quickly woody plants seal off wounds to live tissue; however, research does indicate that plants can react to physical wounds very quickly – within minutes. Why take a chance? Treat quickly after making the cut.
Second, the investigators did good follow-up. They didn’t just look at whether the stumps had re-sprouts. They also looked at sprouting from lateral roots within a 30 cm radius. The researchers checked the stumps at 6, 12, and 18 months after treatment. Most of the treated privet stumps likely died within the first 6 months in this study. However, as the authors note, that is not necessarily the case with different species of invasive woodies.
Third, the study reached important conclusions that really provide guidance to those in the field. It found that November treatments were more effective than April ones – 95% vs 87% mortality. The study found that glyphosate outperformed triclopyr in the November treatments – 97% to 91% control. The authors note that this suggests that “glyphosate is more effective than triclopyr for controlling species prone to lateral root sprouting.”
Finally, the authors found that lower than labeled concentrations of herbicide were effective at controlling privet. This conclusion may not be applicable to all species, but it does suggest that you should be safe using the lowest rates recommended on the label for cut stump and cut stem treatments.