By: Clara Barton

Basal bark treatment is one of the most effective methods for controlling invasive Amur honeysuckle, but it is not unusual to find treated shrubs that continue producing living shoots for weeks or even months after treatment. Should these plants be left alone to die from the original treatment? Or should they be sprayed with a follow up treatment? During the summer of 2026, I tested two follow-up herbicide treatments on surviving honeysuckle resprouts to determine whether additional treatment could improve control and reduce the risk of long-term survival.

Key Takeaways:

• Basal bark treatment continued to kill many resprouting shrubs long after application.
• Glyphosate eliminated surviving resprouts faster than any other treatment tested.
• Crossbow was effective but acted more slowly.
• Most untreated resprouts eventually died, though some remained alive and one continued producing new growth.
•  Follow-up treatment may not be necessary for every resprout, but it can speed control and reduce uncertainty.

Background

Amur honeysuckle (Lonicera maackii) is one of the most troublesome invasive shrubs in Midwestern woodlands. Its ability to leaf out early, retain leaves late into the fall, and form dense thickets allows it to outcompete many native woodland plants. Fortunately, we have several effective tools for controlling it, including basal bark herbicide treatments.

Previous research conducted at Nachusa Grasslands found that basal bark applications of triclopyr resulted in approximately 98.4% mortality of treated Amur honeysuckle plants (Hogan et al. 2024). The study also showed that many treated shrubs continued to leaf out and appear alive for some time after treatment before ultimately dying.

While monitoring previously treated areas at Oak Corners, I noticed several honeysuckle shrubs producing living resprouts despite having already received basal bark treatment. These observations raised a practical management question. If a plant is still producing resprouts after treatment, is it worth applying an additional herbicide treatment, or is it better to simply allow the basal bark treatment more time to work?

More specifically, I wanted to know whether treating surviving resprouts could improve control, reduce the chance of recovery, and shorten the amount of time managers spend monitoring plants that appear to have survived.

Blog post summarizing paper: A Study on Controlling Bush Honeysuckle | grassland restoration network

Experimental Design

On June 11, 2026, I selected and marked thirty honeysuckle plants with visible resprouts at the experiment site. All plants had previously received a basal bark treatment but were still showing evidence of survival.

Each plant was marked, flagged, photographed, and assigned to one of three treatment groups:

Treatment Group	Number of Plants
Control (no additional treatment)	10
3% v/v glyphosate + 0.5 oz/gal LI-700	10
2% v/v Crossbow + 0.5 oz/gal MSO	10

Results

Key Findings

• Glyphosate achieved 100% mortality within 10 days of treatment.
• Crossbow achieved 100% mortality within 24 days of treatment.
• The control group experienced 70% mortality during the monitoring period.

Monitoring revealed differences among the treatment groups within the first ten days after treatment. At the initial assessment on June 22, all glyphosate-treated plants were dead, while approximately 60% of the Crossbow-treated plants had died. Most control plants remained green and alive at that time.

By July 6, all plants in the Crossbow treatment group had died, resulting in complete mortality for both herbicide treatments within the first month of the study. In contrast, mortality in the control group occurred more gradually throughout the summer. Some control plants steadily declined and died, while others remained alive for the duration of the monitoring period.

During the final assessment on August 18, three control plants remained alive. Two appeared largely unchanged from earlier observations, while one continued producing vigorous new shoots despite having previously received a basal bark treatment. I believe two of these plants were on their way out, but I had to stop monitoring these plants due to some contractor work that was beginning in the area. The remaining surviving plants were treated with herbicide on August 24th 2026.

Discussion and Conclusions

This experiment builds upon previous honeysuckle research conducted at Nachusa Grasslands, but it addresses a different question. Hogan et al. (2024) evaluated the effectiveness of initial basal bark triclopyr treatments and found approximately 98.4% mortality across nearly 800 treated Amur honeysuckle plants. The shrubs included in this experiment had already received a basal bark treatment and were selected specifically because they still contained living resprouts. As a result, this study was not designed to test whether basal bark treatment works, but rather what should be done when a treated shrub appears to survive.

The control plants in this study help reinforce the findings of Hogan et al. Several shrubs that still had living stems and resprouts early in the summer gradually declined and died over the course of the monitoring period. These observations suggest that the original basal bark treatment was continuing to work long after the initial application and that the presence of living foliage or resprouts does not necessarily indicate treatment failure. Glyphosate and Crossbow both accelerated mortality. Glyphosate-treated plants reached complete mortality within ten days, while Crossbow-treated plants reached complete mortality within several weeks. The control plants followed a much slower trajectory, with mortality continuing throughout the summer. The control group also raises an important question about retreatment. Seven of the ten control plants died during the study without receiving any additional herbicide. Given that observation, immediate retreatment of every resprouting honeysuckle may not always be necessary. In some cases, allowing more time for the original basal bark treatment to work may be a reasonable approach, particularly when time and resources are limited.

Not all resprouts behaved the same way, however. While many control plants gradually declined, plant #5 from the control group continued producing vigorous new shoots throughout the study. This suggests that follow-up treatments may be most valuable for plants that continue generating new growth or remain alive long after surrounding treated plants have declined. Waiting to see which plants persist may help identify the individuals most likely to benefit from additional treatment.

Both follow-up treatments improved control of surviving resprouts, and glyphosate provided the fastest response. At the same time, the control group demonstrated that substantial mortality can continue to occur months after a basal bark treatment has been applied.

Study Limitations

This experiment included only 30 plants within a single management area and was monitored for one growing season. Additional monitoring would be needed to determine whether the remaining control plants ultimately die or continue producing new growth.

Further Readings on Basal Bark from the GRN

• Basal Bark Herbicide Treatments for Invasive Shrubs – the Type of Oil Carrier Matters! | grassland restoration network
• Post-Burn Basal Bark Treatments: A Game Changer for Invasive Shrub Control | grassland restoration network
• Invasive Shrub Treatment Methods – Cut Stump and Basal Bark Comparison | grassland restoration network
• A Study on Controlling Bush Honeysuckle | grassland restoration network
• A family affair: Successful control of invasive honeysuckle with basal bark herbicide | grassland restoration network

Reference

Hogan, K. F. E., Baker, K., Bach, E. M., & Barber, N. A. (2024). Basal bark herbicide treatment of Lonicera maackii (Amur honeysuckle) is effective regardless of application timing, with limited nontarget effects on native plant diversity. Ecological Solutions and Evidence, 5, e12332. https://doi.org/10.1002/2688-8319.12332