UW-Madison Leads Field Day for Woody Invasive Plant Management

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Through expert presentations and a tour of test plots in Fitchburg, Wisconsin, the Renz Weed Science Lab at the University of Wisconsin-Madison showcased best practices for parks and forestry management professionals as well as municipality employees to control incompatible vegetation on their managed land.

The efficacy of parks and forestry management programs often hinges on two key factors: the vegetation control strategies they use and the resources they receive to execute those strategies. From a funding perspective, vegetation managers are often challenged to do more with less, which makes the use of effective control methods exceedingly important.

Many practitioners rely on mechanized mowing to control incompatible or problematic vegetation throughout parks or forestry sites. While this strategy is effective at providing immediate results, Extension specialists with the University of Wisconsin-Madison (UW-Madison) are working to educate industry professionals and their volunteer partners on the benefits selective herbicide applications can provide to the environmental and economic impact of their respective programs.

After conducting five Roadside Invasive Plant Management Workshops in 2019, the Renz Weed Science Lab at UW-Madison planned to expand its educational offering beyond the transportation sector. Unfortunately, the COVID-19 pandemic derailed plans to conduct in-person learning sessions until this past July. Only this time, park and forestry managers were the target audience.

Enhancing Shrub Management

As part of the Invasive Shrub Management Field Day presented by the Renz Weed Science Lab, Corteva Agriscience, Nutrien Solutions and 4Control, lab representatives and industry experts detailed vegetation management practices that can be used to help park and forestry managers effectively control invasive woody plants without sacrificing environmental sustainability or recreational opportunities for park visitors. Goals associated with this educational event aimed to help more than 50 attendees from the United States Department of Agriculture, Wisconsin Department of Natural Resources, local municipalities and departments of public works achieve optimum results through the use of industry-leading vegetation management strategies.

Targeted Vegetation

In nearly any setting, high densities of invasive plants can inhibit the regeneration of desirable tree species. As non-native vegetation depletes seed sources in the canopy and limits light levels at the ground level, these unwanted plants can threaten the long-term status of parks as woodlots.

In Fitchburg, Wisconsin, where the 2022 Invasive Shrub Management Field Day was held, two particular invasive plant species were the primary focus of vegetation control strategies: common buckthorn (Rhamnus cathartica) and large multi-stemmed bush honeysuckle (Lonicera spp.) shrubs.

In McGaw Park, bush honeysuckle poses a developmental threat to large legacy oak trees that dominate the park canopy. Comparatively, the presence of buckthorn throughout the UW-Madison Arboretum Grady Tract inhibits the regeneration of native plant species, trees and understory vegetation. Several vegetation management techniques can be used to control this problematic vegetation. However, research leading up to the field day suggests that certain strategies are more effective from a results and cost-efficiency standpoint.

Buckthorn can impede native plant development, posing a risk to trees and understory vegetation.

Strategies Used for Invasive Woody Shrub Management

Industry professionals and their vegetation management partners tested numerous methods to assess best management practices for the control of bush honeysuckle and buckthorn throughout McGaw Park and Grady Tract, respectively. While only herbicide-based applications were demonstrated during the field day, common approaches to management were discussed, along with pros and cons for each.

  • Manual Removal
    Removing the above- and below-ground reproductive parts of targeted vegetation is effective, but also labor-intensive. This method also causes inadvertent soil disturbance.
  • Forestry Mowing
    Forestry mowing is effective at removing and shredding stems and woody material, but it’s expensive and often leads to resprouting.
  • Prescribed Fire
    Prescribed fire supports the removal of above-ground tissue (and sometimes roots). While many native plants thrive under fire, this practice causes burning hazards and resprouting.
  • Direct Flaming
    Heating the root crown of targeted vegetation with a propane torch offers selective control that is less effective on native plants. However, this method is not effective on all shrubs and also poses a fire hazard.
  • Goats
    While goats offer selective control of targeted vegetation, they are expensive and often take years to eliminate invasive shrubs.
  • Herbicides
    The final vegetation management techniques tested were four different methods of chemical control:
    • Hack and squirt
    • Foliar
    • Cut surface
    • Basal bark

Using these selective herbicide applications offered high levels of control on both buckthorn and honeysuckle while limiting damage to off-target vegetation. Results achieved more than a year after treatment indicate that these applications are not only cost efficient, but also highly effective on large infestations of incompatible vegetation.

Product Performance by Technique

A total of eight herbicide products were used to assess the performance of the four chemical control methods tested by the Renz Weed Science Lab. As a sponsor of the field day, Corteva Agriscience was represented by two products: Vastlan® herbicide and Tordon® 22K herbicide. Tank mixtures featuring Vastlan herbicide achieved 100% control of buckthorn and bush honeysuckle using a foliar treatment method, while hack-and-squirt treatments featuring Vastlan achieved 100% control of buckthorn as well. Comparatively, cut-surface treatments featuring Tordon 22K controlled 100% of both species.

Here’s a performance breakdown of all chemical control methods tested throughout McGaw Park and Grady Tract:

McGaw Park
Three vegetation control methods were tested on bush honeysuckle shrubs throughout McGaw Park in the spring of 2021: foliar herbicide, foliar herbicide plus forestry mowing, and cut-surface treatments. A CO2 pressurized single-nozzle sprayer was used to deliver approximately 50 gallons per acre for each application. While certain herbicide products used for each method achieved 100% control, the average cost per treated shrub fluctuated from one strategy to the next. In nearly all cases, the cost of application accounted for more than 90% of the required investment.

Foliar Herbicide Treatment

  • Developmental stage: Flowering shrubs
  • Application timing: May 2021
  • Average cost/shrub:Results:

Foliar Herbicide Treatment + Forestry Mowing in Late 2020/Early 2021

  • Developmental stage: Resprouted after forestry mowing
  • Application timing: June 2021 and September 2021
  • Average cost/shrub: $0.01-$0.21 (June)/$0.02-$0.21 (September)
  • Results: Applying herbicides later in the year at a higher rate achieved 100% control for all tested herbicide products.

Cut-surface Treatment

  • Developmental stage: <2 m tall (leafed out but not yet flowering)
  • Application timing: April 2021
  • Average cost/shrub: ~$6.00
  • Results: All herbicide products used achieved 100% control by June 2022.

Comparison of effectiveness of foliar treatments applied at low (Vastlan at 1% v/v and Roundup at 1.5% v/v), medium (3% v/v) and high (5% v/v) rates to resprouting shoots in summer (June 2021) or fall (September 2021). Control was estimated in June 2022 (12 and 9 months after treatment).
2021. Invasive Shrub Management Field Day – McGaw Park 2022. UW-Madison Renz Weed Science Lab.

Grady Tract
Four chemical control methods were tested on invasive buckthorn species throughout Grady Tract: hack and squirt, basal bark, foliar herbicide and cut-surface treatments. Foliar treatments were applied using the same CO2 pressurized single-nozzle sprayer as McGaw Park. However, the PSI was reduced for cut-surface and basal bark treatments, while a syringe was used to apply herbicide as part of the hack-and-squirt method. 

Hack and Squirt

  • Developmental stage: >2.5 m/average diameter of 7 cm
  • Application timing: April 2021
  • Average cost/shrub: $0.50-$1.52
  • Results:

Basal Bark

  • Developmental stage: 1.0 m - 2.5 m tall
  • Application timing: April 2021
  • Average cost/shrub: $0.29-$0.51
  • Results: All herbicide products used achieved 100% control by July 2022

Foliar Herbicide

  • Developmental stage: Single-stemmed, fully leafed-out buckthorn shrubs (0.25 m – 1.0 m tall)
  • Application timing: May 2021
  • Average cost/shrub: $0.09-$0.14
  • Results: Three of five chemistries tested achieved 100% control by July 2022

Comparison of effectiveness of stem injection, basal bark, cut surface and foliar treatments on common buckthorn. Evaluation completed on July 6, 2022 (412-435 days after treatment). For a complete breakdown of application rates and treatment mixes, click here.
2021. Invasive Shrub Management Field Day – UW-Madison Arboretum Grady Tract 2022. UW-Madison Renz Weed Science Lab.

These results underscore three key considerations for park and forestry managers:

  • Selective herbicide applications can be used to effectively treat problematic plants that impede the development of desirable vegetation.
  • Herbicide treatments can help park and forestry managers reduce maintenance costs thanks to increased efficacy
  • Applying the right products at the right time with the right method is essential to achieving optimum results.

To view a complete breakdown of the equipment, application rates and estimated labor costs associated with each product and treatment method tested, visit the links below:

McGaw Park Results (Bush Honeysuckle)
Grady Tract Results (Buckthorn)

Regardless of the herbicide application method vegetation managers use on their managed land, it’s important that this work is completed by licensed applicators. Ensuring proper application can not only enhance control of incompatible vegetation, but also support the development of desirable vegetation throughout parks and forestry settings. Subsequently, these results can increase biodiversity for native wildlife species, which can effectively crowd out problematic species and lower long-term maintenance costs in the process.

To learn more about the ways in which vegetation management programs can positively impact environmental sustainability, visit HabitatWithHerbicides.com.

Tordon 22K is a Restricted Use Pesticide. Vastlan is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.


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