Got Nature? Blog

Purdue Landscape Report: There have been a significant number of questions and problems regarding triclopyr that have come up this growing season.

Figure 1. Confirmed damage from triclopyr on sassafras shows the growth regulator-type injury on leaves. Photo courtesy of the Office of the Indiana State Chemist.

Several of these problems have come through the Purdue Plant and Pest Diagnostic Laboratory from landscapers, nurseries, and property managers.

General Information about Triclopyr
Triclopyr is a selective systemic herbicide belonging to the pyridine class. It is primarily used to manage woody plants, vines, and some broadleaf weeds. Unlike glyphosate, a broad-spectrum herbicide, triclopyr specifically targets the growth hormones in dicotyledonous plants, making it effective in controlling species that are difficult to manage with other herbicides. It works by mimicking plant hormones, disrupting normal growth processes, and leading to the death of the treated plant (Fig. 1).

What Triclopyr Controls
Triclopyr is utilized in various settings to control unwanted vegetation. It is effective against species such as:

• Woody Plants: Includes trees like tree of heaven and callery pear and shrubs like autumn olive and honeysuckle (Fig. 2).
• Vines: Particularly those that can outcompete native flora, such as kudzu or English ivy (Fig. 3).
• Broadleaf Weeds: Some herbaceous plants that pose ecological or agricultural problems.

Figure 2. Invasive plants, such as, Pyrus calleryana (callery pear) can be controlled by triclopyr.

Figure 3. Invasive vines, such as Hedera helix (English ivy) can be controlled via multiple applications of triclopyr.

Where and When Triclopyr is Used
Triclopyr is applied in a range of environments, including:

• Forestry: To clear invasive species and manage forest regeneration.
• Agriculture: To control weeds and shrubs that interfere with crop production.
• Aquatic Areas: Formulations that are safe for aquatic environments help manage invasive species near water bodies.
• Rights-of-Way: To maintain clear paths and prevent the spread of invasive plants.

Timing of application is crucial. Triclopyr is most effective when applied during the growing season when plants are actively taking up nutrients and can transport the herbicide throughout their system.

Figure 4. Hack and squirt treatments with triclopyr is a common method to control invasive trees. Photo by Lenny Farlee.

Movement in the Plant
Triclopyr is absorbed through foliage and roots and is translocated systematically within the plant. Once inside, it moves upward through the xylem and downward through the phloem (ambimobile). This systemic movement allows triclopyr to affect not just the treated areas but also parts of the plant that are not directly sprayed. This attribute makes it effective for managing large, established plants, specifically through hack and squirt treatments (Fig. 4).

For the full article and conclusion sharing how Triclopyr is a valuable tool for managing invasive and woody plants view: The Summer of Triclopyr: Mounting evidence for off-target damage.

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Resources:
Find an Arborist video, Trees are Good-International Society of Arboriculture (ISA)
ID That Tree, Playlist, Purdue Extension – FNR YouTube Channel
Invasive Species Playlist, Playlist, Purdue Extension – FNR YouTube Channel
A Woodland Management Moment, Playlist, Purdue Extension – FNR YouTube Channel (Against Invasives, Garlic Mustard, Autumn Olive)
Woodland Stewardship for Landowners, Playlist, Purdue Extension – FNR YouTube Channel (Common Buckthorn, Japanese Barberry)
Report Invasive Species, Purdue Invasive Species
The GLEDN Phone App – Great Lakes Early Detection Network
Invasive Plants of the Eastern U.S.: An Introduction to the Problematic Non-Native Species, The Education Store, Purdue Extension’s resource center
EDDMaps – Early Detection and Distribution Mapping System
Episode 11 – Exploring the challenges of Invasive Species, Habitat University-Natural Resource University
What Are Invasive Species and Why Should I Care?, Purdue Extension-FNR Got Nature? Blog
Emerald Ash Borer Information Network, Purdue University and Partners
Aquatic Invasive Species, Illinois-Indiana Sea Grant (IISG)
Invasive plants: impact on environment and people, The Education Store, Purdue Extension’s resource center
Subscribe Purdue Extension-Forestry and Natural Resources YouTube Channel

Kyle Daniel, Commercial Landscape and Nursery Crops Extension Specialist
Purdue Horticulture & Landscape Architecture