Exotic Bush Honeysuckle Control Trial

Cooperators: Purdue University Department of Forestry and Natural Resources,
Vigo County Parks Department, and Townsend Chemical

Objective: Test efficacy of various herbicide combinations in selectively controlling
Asian bush honeysuckles in a mature forest setting, while protecting native understory vegetation,
using hand application equipment.

Test Treatments:

1. Control
2. Foliar, 4% Garlon 3A (triclopyr) – April 4, 03
3. Foliar, 3% Garlon 3A + 1/8% Arsenal (imazapyr) – April 10, 03
4. Foliar, 5% GlyproPlus, (glyphosate) – April 10, 03
5. Foliar, 4% Garlon 3A – Nov. 4, 02
6. Foliar, 3% Garlon 3A + 1/8% Arsenal – Nov. 4, 02
7. Foliar, 4% GlyproPlus – Nov. 4, 02
8. Basal Bark, 20% Garlon 4 in AX-IT basal oil – Jan. 7, 03
9. Streamline, 20% Garlon 4 in AX-IT basal oil – Jan. 7, 03
10. Cut Stump – Pathway – Feb. 13, 03
11. Cut Stump – 20% Garlon 4+AX-IT – Jan. 21, 03

Treatments 2 – 7 tested three combinations of foliar herbicides applied using backpack sprayers in
both early spring and late summer in an effort to minimize damage to native understory vegetation.
Treatment 8 applies herbicide in an oil carrier (AXIT), with an adjustable cone nozzle on a backpack
sprayer, to the lower 15 inches of the stem. The oil penetrates the bark and delivers the herbicide into
the plant’s vascular system. Treatment 9 is a variation on basal bark treatments in that the herbicide/oil
mix is sprayed on the base of the stem as a pencil-lead thick stream. This is supposed to be effective
on young, small diameter stems while reducing overall the amount of herbicide applied. Treatments 10
and 11 involve cutting the shrubs off at the base using a chainsaw and spraying the freshly cut stump
surface with herbicide. This was done as a two-person crew (Chainsaw operator and applicator using
a backpack sprayer)

Results:

Table 1 presents Asian bush honeysuckle percent mortality resulting from the respective treatments. Shrub size influenced treatment efficacy. The largest size class (8’+ tall) was difficult to thoroughly treat with foliar applications using backpack sprayers. Inevitably, the highest portions of the crowns received little herbicide. Both cut stump treatments were 100% effective in killing the largest size class. The basal bark treatment was only partially effective (43% control) (Figure 2), while streamline delivered far too little herbicide to most of these large shrubs to be effective.

Foliar applications of glyphosate and triclopyr+imazapyr were very effective on intermediate (4.5’ – 8’) and
small (2’ – 4.5’) size shrubs, in both the spring and fall applications (Figures 3 - 6). Triclopyr alone produced
only 56% mortality when applied to intermediate size shrubs in the spring and only 4% mortality in the fall.
The basal bark treatment did not improve with the smaller two size classes. The streamline treatment
killed approximately 30% of the shrubs in both the smaller size classes which was not significantly different
from the basal bark treatment where more herbicide is being applied. Cut stump treatment efficacies declined
a little in the intermediate size class and significantly in the small size class shrubs. This was due to the
increasing difficulty of a chainsaw operator finding and cutting smaller shrubs.

Recommendations:

1. Treatments need to be tailored to bush honeysuckle stand structure.
2. Cut stump treatments should be used where large, mature shrubs predominate.
   Cut stump treatments can be applied throughout the year except in spring when the sap is rising.
3. Where accessible (along forest edge or trails and roads), large, mature bush honeysuckle
   can be treated with foliar applications using high-pressure applicators mounted on tractors, trucks, or ATVs.
4. In intermediate and small size class stands use foliar applications of glyphosate at higher rates
   (4% of 4lbs. a.i./gal.). Foliar applications of triclopyr (4%) may be effective during the growing season
   but are not recommended for early spring and late fall applications. Adding 1/8% of imazapyr to the
   triclopyr mix is equally effective as glyphosate for early spring and late fall applications.
5. In bush honeysuckle stands of mixed size classes, a combination of cut stump and foliar treatments should be used.
6. Follow-up treatment will always be needed. Monitor treated areas for two to three years and reapply treatments as needed.
7. For large landowners, treatment of individual bush honeysuckle stands should be prioritized to best
   utilize limited resources to meet organizational objectives.

Ongoing Research:

Additional research is being conducted on basal bark treatments to try to develop protocols that will
assure the successful application of this option to bush honeysuckle control. Tests involve five different
herbicide combinations, four different oil carriers, six different application dates over the course of one year,
applied to two different shrub size classes.

Cost estimates are being developed for different control strategies applied under a range of bush honeysuckle
stand characteristics.

Contact:

Ron Rathfon, Extension Forester
Purdue University, Department of Forestry & Natural Resources
12000 Purdue Farm Road
Dubois, IN 47527
812-678-5049
ronr@purdue.edu

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