Invasive shrubs threaten natural areas in the Midwest and Great Lakes region, out-competing native plants, reducing biodiversity and habitat, and altering ecosystem functions. Some of these woody invaders, including common buckthorn and bush honeysuckle, increase the risk for the spread of human pathogens, by fostering habitat for ticks and other disease vectors. The bottom line is, these invasive woody plants are impacting natural areas and should be managed.
Management of woody invasive plants can be challenging. Small, young plants can be controlled by pulling or digging out the entire root system. However, over time, shrubs can develop into large, dense infestations with deep roots that make this approach impractical. Throughout the Midwest it is common to see mature stands of bush honeysuckle (Lonicera spp.), including Amur (L. maackii), Morrow’s (L. morrowii), Tartarian (L. tatarica), and showy fly honeysuckle (L. x bella). Forest understories can also be thick with common buckthorn (Rhamnus cathartica). At this stage of infestation, the most cost-effective management methods typically involve the use of herbicides. When applied properly, herbicides can restore forest health and ecosystem function. Since many different herbicides can be applied using different methods, it can be complicated to select the best technique, the most appropriate herbicide, and the optimal application rate.
The Renz Weed Science Lab at the University of Wisconsin conducted demonstrations of typical restoration practices that use herbicides for controlling common buckthorn and invasive bush honeysuckle. They tested foliar spray, cut surface application, basal bark spray, and stem injection methods at several sites across Wisconsin between 2021-2022. Trials utilized common herbicides for controlling shrubs including triclopyr, glyphosate, imazapyr, and aminocyclopyrachlor. Researchers collected data on the effectiveness of a combination of each method and chemical. They also assessed the impact to nearby vegetation and determined the cost of implementing each method. These demonstrations are intended to help land managers select the most effective methods and herbicides to achieve their site restoration goals.
You can take a virtual tour of the lab’s demonstration sites to see the results. A summary of each site, along with pictures of the results from each method, can be viewed as part of the tour. You can also find information on the cost of each demonstrated herbicide method.
The Renz Lab found that after one year after treatment, most methods demonstrated >90% control of the target plants, highlighting that many effective control options exist. The cost of application is an important factor when selecting a treatment method. Cost varies considerably among treatments, depending on the density and size of invasive shrubs at the site. Methods that involve cutting the stems are the most expensive. Other costs, while less, were mostly influenced by the cost of labor (>75% of costs). Overall, the important factors that need to be considered when selecting a treatment method include:
- the size of the infested area
- the size(s) of the shrubs in the infestation
- desirable species nearby
- herbicide selectivity, activity, and persistence in the soil
- physical site factors such as soil type, organic matter, and depth to the water table
Visit the Renz Lab project webpage to learn more and stay tuned for future demonstrations and tours.
This article was written by Michelle Beloskur, Coordinator of the Midwest Invasive Plant Network, with contributions from Matthew Wallrath, Coordinator of the Wisconsin First Detection Network, and the Renz Weed Science Lab at the University of Wisconsin-Madison.
