Triclopyr Application Timing and Concentration Influence Low-Volume Basal Bark Efficacy on Chinese Privet (Ligustrum sinense)

• Published in: Invasive plant science and management Vol. 9; no. 4; pp. 235 - 241
• Main Authors: Enloe, Stephen F, O'Sullivan, Sarah E, Loewenstein, Nancy J, Brantley, Eve F, Lauer, Dwight K
• Format: Journal Article
• Language: English
• Published: Cambridge, UK The Weed Science Society of America 01.10.2016; Cambridge University Press
• Subjects: Bark; Basal bark treatment; Bottomland; Defoliation; Forests; Herbicides; individual plant treatment; invasive plant control; Ligustrum sinense; Mortality; Roadsides; Seeds; Winter; woody plant control; United States > US; ASW, USA, Alabama; USA, Alabama, Auburn; USA, Southeast; Triclopyr; individual plant treatment; Basal bark treatment; woody plant control; invasive plant control; Chinese privet, Ligustrum sinense Lour
• ISSN: 1939-7291; 1939-747X
• DOI: 10.1614/IPSM-D-16-00028.1

Chinese privet is an invasive shrub that commonly infests roadsides and bottomland forests across the southeastern United States. Its aggressive growth and ability to prolifically sprout from the root collar and shallow lateral roots makes control very difficult. Individual plant treatment methods such as low-volume basal bark herbicide application with triclopyr are commonly used for Chinese privet control. However, little research has been done to examine optimal triclopyr concentrations and application timings for the low-volume basal bark method. Furthermore, little is known regarding basal bark treatment efficacy when plant size varies. To address these questions, field studies were conducted from 2009 to 2011 at two locations in east-central Alabama near Auburn and Opelika. The triclopyr butoxyethyl ester formulation was applied in January or March to Chinese privet shrubs across a range of sizes in a commercially available basal oil carrier at 24 (5% v/v−1), 48 (10% v/v−1), and 96 g L−1 (20% v/v−1). Additionally, a triclopyr butoxyethyl ester ready-to-use formulation (90 g L−1) was applied at 100% v/v−1. Canopy defoliation, sprout height, and mortality were quantified at 6, 12, and 18 mo after treatment. Triclopyr at all concentrations was highly effective in defoliating Chinese privet and reducing height of new basal sprouts. However, mortality was concentration dependent. The 90 and 96 g L−1 treatments resulted in 88 and 89% mortality across timings, while the 24 and 48 g L−1 treatments resulted in 63 and 76% mortality. March applications were less effective as basal diameter increased, especially at the lower triclopyr concentrations where mortality fell to less than 40%. These results indicate that triclopyr is an effective treatment for Chinese privet control, but efficacy is influenced by concentration, application timing, and plant size. Nomenclature: Triclopyr; Chinese privet, Ligustrum sinense Lour. Management Implications: Chinese privet is an aggressive shrub that is especially problematic in bottomland hardwood areas of the southeastern United States. Many land managers use individual plant treatment (IPT) methods to control Chinese privet in these areas to improve selectivity and reduce non-target damage. However, little has been published regarding IPT methods for Chinese privet control. We examined basal bark treatment with triclopyr across a range of concentrations as a method for controlling Chinese privet at January and March timings. In general, we found that winter (January) applications of triclopyr from 24 to 96 g L−1 resulted in greater than 90% defoliation while applications of 48 to 96 g L−1 achieved greater than 80% mortality. Early spring (March) applications of 24 to 96 g L−1 resulted in greater than 80% defoliation. However, application concentrations of 90 to 96 g L−1 were required to achieve 80% mortality. These results demonstrate that winter applications of triclopyr as a low-volume basal bark treatment may be effective at lower concentrations than the commercial standard of 96 g L−1. However, March applications will likely require either the 90 or 96 g L−1 concentration for successful control.