Comparison of Non-herbicide Methods for Control of Invasive Bush Honeysuckle as Preparation for a Prescribed Burn

View the project final report

Commodities

• Animals: goats

Practices

• Animal Production: grazing management
• Natural Resources/Environment: habitat enhancement, Invasive Species Control; Prescribed Burn Preparation

The 110 wooded acres on my farm are degraded habitat dominated by invasive and undesirable woody species, including bush honeysuckle (Lonicera spp.) and Osage orange trees. Prior to European colonization, these wooded areas were dominated by prairie grasses with scattered white and northern red oaks, a community referred to as oak savanna. In protected slopes and ravines, the overstory may have shifted to a more closed canopy, oak-dominated natural community. Once common, these natural communities rarely persist on landscapes today, however within the 110 acres of woodland on my farm, many large white and red oaks remain.

Oak savanna is a fire-dependent landscape, requiring fire to remain healthy and diverse. A century of fire suppression has contributed to the proliferation of invasive woody shrubs, especially bush honeysuckle.

Prescribed burning is an important forest management tool, but a heavy infestation of invasive bush honeysuckle removes that tool from the toolbox. Bush honeysuckle kills herbaceous groundcover, which is required fuel for a prescribed fire.

Bush honeysuckle blocks sunlight to the forest floor by leafing out first in the spring and keeping its leaves longest in the fall. Additionally, it creates a dense understory that shades the forest floor during the growing season. Honeysuckle also takes moisture and nutrients away from native plants. A severe honeysuckle infestation results in little, if any, herbaceous groundcover underneath. This lack of groundcover promotes soil erosion. Furthermore, a prescribed burn, necessary to improve forest health, is simply not possible because there is no fuel for a fire.

The standard practice for bush honeysuckle control today is treatment with the herbicide glyphosate. However, blanketing our woodlands in glyphosate is detrimental to the health of humans, desirable plants, insects, and animals (van Bruggen, et al., 2021; Smith, et al., 2021).

The goal of this study was to determine how to control bush honeysuckle in an environmentally sound, sustainable way, that is, without the use of herbicides, to prepare for a prescribed burn.

Different treatment sequences of targeted goat grazing and mechanical clearing were evaluated on four five-acre test units. The treatments were administered in spring/summer 2024, fall 2024, and spring/summer 2025. Metrics included honeysuckle stem count, honeysuckle percent cover, and honeysuckle average height. These metrics were measured in 21 ft by 21 ft square test plots, randomly located within each test unit, before and after each treatment. The same metrics were measured in an untreated control plot. Photos were taken for visual evaluation.

At the end of the study, all test plots had lower honeysuckle infestation compared to the untreated control plot. Treated test plots had about 10 honeysuckle stems compared to 75 in the untreated control plot. Honeysuckle percent cover in the test plots was less than 10% compared to 80% in the untreated control plot. Average honeysuckle height in the test plots was about 7.5 ft at the start of the study and about 3.5 ft at the end of the study.

Despite the voracious appetite of the goats and their effectiveness at defoliation up to six feet high, they are unable to reach mature honeysuckle, which can grow to heights of 15 ft or more. Therefore, mechanical clearing is absolutely necessary in conjunction with goats to eradicate mature stands of honeysuckle. Exactly when mechanical clearing occurred within the two-year study period did not make a measurable difference, but from a practical standpoint, an initial treatment of goat grazing before mechanical clearing made clearing easier, safer, and more efficient because machine operators could see where they were going.

Based on this two-year study, the recommended method for controlling a severe infestation of bush honeysuckle without herbicide is a treatment sequence of (1) targeted goat grazing in the spring to open up the understory for visibility, (2) heavy mechanical clearing in the fall to remove honeysuckle by the roots as much as possible, especially the tall honeysuckle that goats can’t reach, and (3) goat grazing the following year to knock back resprouts and new seedlings.

There is generally not enough herbaceous groundcover to carry a strong fire yet, including where we seeded with native grasses at ~1 lb/ac. We plan a prescribed fire in winter/spring 2026, but we expect it to be spotty, burning best in areas of continuous leaf litter from the oak trees. All the test units are expected to burn better than the untreated control area due to dryer, more intact leaf litter in the test units. There isn’t an obvious difference among test units with regard to which will burn best, indicating that the treatment sequence did not have a large impact on preparedness for a prescribed burn.

It will be necessary to continue treatments in subsequent years to prevent the honeysuckle from taking over again. Planned treatments include prescribed burning and more goat grazing to keep honeysuckle under control.

A habitat tour was held on my farm in June 2025 with 54 attendees. At least two attendees have started goat grazing on their farms after seeing the improvement goats have made in my woodland.

van Bruggen, A.H.C, M.R. Finckh, M. He, C.J. Ritsema, P. Harkes, D. Knuth, and V. Geissen. 2021. Indirect effects of the herbicide glyphosate on plant, animal and human health through its effects on microbial communities. Frontiers in Environmental Science 9.

Smith, D.F.Q, E. Camacho, R. Thakur, A.J. Barron, U. Dong, G. Dimopoulos, N. Broderick, and A. Ccasadevall. 2021. Glyphosate inhibits melanization and increases susceptibility to infection in insects. PLoS Biology 19(5): e3001182.

Objectives:

1. Compare non-herbicide methods for control of invasive bush honeysuckle on 20.6 wooded acres divided into five test units. Methods include targeted goat grazing, manual mechanical cutting, machine pulling, and machine shredding.
2. Evaluate the effectiveness of lightly seeding native grasses to determine if seeding enhances herbaceous groundcover
3. Assess which methods promote sufficient herbaceous groundcover to enable a future prescribed burn
4. Determine which method sequence, if any, should be expanded to larger acreage on my farm
5. Share findings with the community to encourage environmentally sound approaches for brush control

Study Overview:

Two areas, A1 and A2, were identified within 110 acres of degraded oak-dominant natural communities and divided into five test units as shown in Figure 1. Adjacent area A5 was used as an untreated control for the study. Areas A1 and A2 both have steep ravines (up to 60% slope) with incised creeks running through the bottoms. At the start of the study, all areas had a thick understory of bush honeysuckle, a severe infestation. For historical reference, Figure 2 shows aerial views of the farm in 1939 and 2019. In 1939, the woodland is a more open landscape in contrast to the completely closed canopy in 2019.

Table 1 summarizes the original study design. Modifications made in the field are discussed in the “Materials and Methods” section, and the final study design is shown in Table 3.

Table 1: Original study design.

In Table 1, “Mulch” means shredding with a mulching head on a skid steer. “Goats&Cut” means after goats have grazed for a couple days, then manually cut honeysuckle taller than goat-graze height to near ground level. “Cut” means manually cut all honeysuckle with chain saws and hand tools to near ground level. “TBD” means to be determined based on treatment effectiveness in 2024.

Goats can graze to a height of about 6 ft, whereas honeysuckle grows to 15 ft tall or more. Therefore, mechanical removal was included in each method to drop tall honeysuckle to near ground level.

To test the value of seeding, native grass seed (~1 lb/acre) was hand broadcast in half of each unit with the timing recorded.

This study was intended to answer the question of which method sequence, with or without seeding, provides the best preparation for a future prescribed burn.