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Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 182
TREATING JAPANESE BARBERRY (BERBERIS THUNBERGII)
DURING THE DORMANT SEASON
Jeffrey S. Ward and Scott C. Williams1
Abstract.—Japanese barberry (Berberis thunbergii) is an invasive shrub that can
suppress forest regeneration and increase the risk of exposure to Lyme disease. In 2008,
we began a study in central Connecticut to examine the effi cacy of treating barberry
infestations during the dormant season (October-March). Techniques included
basal spray (triclopyr in oil) and clearing saw cutting with a wet-blade application of
triclopyr. Dormant season techniques were compared with a glyphosate foliar spray
applied in September. Foliar application resulted in a greater reduction of barberry
cover (94 percent) compared to basal spray (84 percent) and wet-blade treatments
(74 percent). Treatment eff ectiveness did not diff er among months for either of the
dormant season techniques. Labor costs did not diff er among techniques, averaging
0.13 hours/acre/percent cover (i.e., 3.9 hours for a 1 acre stand with 30 percent
barberry abundance). ere was a large diff erence among treatments in amount of
herbicide applied with 0.6 (±0.1), 1.4 (±0.4), and 2.8 (±0.4) ounces/acre/percent cover
for wet-blade clearing saw, foliar spray, and basal spray applications, respectively. While
not as eff ective as foliar spraying, wet-blade clearing saw and basal spray applications
provide an opportunity to control barberry during the dormant season. Wet-blade
clearing saw technique can reduce the amount of applied herbicide.
INTRODUCTION
Controlling invasive species is a challenge for forest managers throughout the central hardwood
region (Barton et al. 2004, Bowker and Stringer 2011, McGill et al. 2008, Moser et al. 2008) and the
greater United States (Miller et al. 2010, Webster et al. 2006). Japanese barberry (Berberis thunbergii
DC) is classifi ed as an invasive shrub in 20 states and 4 Canadian provinces. It is also established in
another 11 states (Natural Resources Conservation Service 2011). Japanese barberry, or barberry
hereafter, is primarily an invader of abandoned agricultural fi elds (DeGasperis and Motzkin 2007,
Mosher et al. 2009). Once established in a forest, it can persist at low light levels (Harrington et
al. 2004), and due to the lack of a seed bank (D’Appollonio 1997), spreads primarily by layering
(DeGasperis and Motzkin 2007, Ehrenfeld 1999).
Invasive species such as barberry aff ect multiple trophic levels in forested ecosystems. Tree seedlings
and native herbaceous plants can be inhibited by dense thickets of barberry and other invasive shrubs
(Collier and Vankat 2002, Gorchov and Trisel 2003, Kourtev et al. 1998, Miller and Gorchov 2004).
Barberry can directly alter soil biota and chemistry (Ehrenfeld et al. 2001), as well as soil structure
and function (Kourtev et al. 2003). In addition, there can be indirect negative eff ects. Higher
earthworm levels have been associated with barberry (Kourtev et al. 1999, Nuzzo et al. 2009) and
honeysuckle (Lonicera spp.) (Madritch and Lindroth 2009). Increased earthworm populations have
been linked to decreased litter layer depth and sequestered carbon (Bohlen et al. 2004), increased
phosphorus leaching (Suarez et al. 2003), and salamander population declines (Maerz et al. 2009).
1Chief Scientist (JSW) and Assistant Scientist (SCW), Connecticut Agricultural Experiment Station,
Department of Forestry and Horticulture, New Haven, CT 06511. SCW is corresponding author: to
contact, email at jeff rey.ward@ct.gov.
Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 183
Invasive shrub infestations can have indirect, adverse eff ects on human health by functioning as
disease foci. Enhanced levels of blacklegged ticks (Ixodes scapularis Say) are associated with Japanese
barberry infestations (Elias et al. 2006, Williams and Ward 2010). ese ticks can transmit the
causal agents of several diseases including Lyme disease (Borrelia burgdorferi Johnson, Schmid, Hyde,
Steigerwalt, and Brenner), anaplasmosis (Anaplasma phagocytophilum eiler), and human babesiosis
(Babesia microti Franga) (Magnarelli et al. 2006). Higher densities of lone star ticks (Amblyomma
americanum L.) infected with the causal agents of human ehrlichiosis (Ehrlichia chaff eensis) and E.
ewingii were found in Amur honeysuckle (Lonicera maackii [Rupr.] Herder) infestations in Missouri
(Allan et al. 2010). Lone star ticks can also transmit the agent of tularemia (Francisella tularensis)
(Staff ord 2007). Increased awareness of the link between invasive shrubs and diseases that aff ect
humans and their pets should increase public support and funding for controlling invasive shrubs
throughout the central hardwood region.
Our earlier research has shown that eff ective barberry control can be accomplished from late spring
through early autumn by a variety of chemical (Ward et al. 2010) and nonchemical methods (Ward
and Williams 2011). Because of environmental concerns and potential to damage nontarget species
when using broadcast herbicide treatments, we developed a two-step process that reduces the amount
of herbicide applied. e fi rst step kills aboveground stems by cutting (clearing saw, mowing) or
heat (prescribed fi re, propane torches). e second step kills the much smaller new sprouts with
herbicide (glyphosate, triclopyr) or directed heat using a propane torch. Two studies were established
to compare the eff ectiveness and costs of diff erent treatments to control invasive species (primarily
barberry) from October through March (dormant season), extending the results of earlier studies that
found that initial control of barberry can be completed from April through September. e specifi c
objectives were: 1) compare wet-blade and basal spray applications during the dormant season, and 2)
determine any restrictions to treating during the dormant season.
STUDY AREAS
In September 2008, the Bicentennial Pond study area was established at Schoolhouse Brook Town
Park in Mansfi eld, CT to compare the eff ectiveness and costs of treatments to control invasive species
(primarily barberry) during autumn and early winter. A second study area, Clover Mill, was established
in a diff erent section of the park in November 2008 to examine control alternatives during winter.
Upper canopies of both study areas were mixed hardwoods (primarily Quercus and Acer with some
Fraxinus, Betula, and Carya). e areas are managed as nature preserves with no sign of earlier harvesting.
METHODS
Design and Measurements
Autumn/Early Winter Treatments
Ten 66 ft by 66 ft subplots were established at Clover Mill for the autumn/early winter treatment
study. Subplots were randomly assigned one of fi ve treatments: foliar spray with glyphosate2
(Prosecutor®, 1 percent solution) in September; wet-blade application with glyphosate (41 percent
solution) in October; wet-blade application with triclopyr (Garlon 4®, 61 percent solution) in
2Mention of a product or company is for informational purposes only and does not constitute an
endorsement by the Connecticut Agricultural Experiment Station.
Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 184
October; basal bark application with triclopyr (2 percent solution in oil) in October; and basal bark
application with triclopyr (2 percent solution in oil) in December. Two replications of each treatment
were established at Clover Mill. Treatment details are given below.
Winter Treatments
e winter treatment study at Bicentennial Pond included two blocks of 12 subplots measuring
66 ft by 50 ft. Within each block, subplots were randomly assigned one of six initial treatments:
January, February, or March basal bark application with triclopyr (Garlon 4®, 2 percent solution in
oil) or January, February, or March wet-blade application with triclopyr (61 percent solution). Next,
subplots within each block were randomly assigned one of two follow-up treatments: foliar spray
with glyphosate (1 percent solution) or triclopyr (3 percent solution) in late May. is provided two
replications of each initial/follow-up treatment combination at Bicentennial Pond.
Measurements
Within each subplot, percent barberry cover was measured utilizing a 5.4 ft2 (0.25 m2) sampling
instrument which consisted of a 4 by 4 grid with which percent barberry cover was determined by
presence/absence within each cell (Ward and Williams 2011). ere were 12 sample points within
each subplot for each treatment combination for a total of 504 sample points. Cover was sampled
in August 2008 (pretreatment) and June 2009 (post-treatment) at Clover Mill, and in November
2008 (pretreatment), May 2009 (before follow-up treatment), and October 2009 (post-treatment)
at Bicentennial Pond. e amount of herbicide applied to each subplot was recorded along with
treatment time.
Treatments
Herbicide sprays were diluted per label instructions and were applied until wet to target foliage
using hand-pressurized backpack sprayers (Solo® Model LCS-2, Newport News, VA). Only foliage
or lower stems of invasive species (primarily barberry) were targeted to minimize impact to native
species. A dye was added (1 percent solution) to the tank mixes to identify clumps that had not been
treated and to prevent spraying clumps more than once. Basal and foliar applications were made with
backpack sprayers. Wet-blade treatments were made using an applicator (Sprout-Less®, Madawaska,
NB, Canada) that was attached to the bottom of a clearing saw blade (Model FS 450, Stihl®, Inc.,
Virginia Beach, VA). e applicator was designed to continually apply a thin fi lm of herbicide to the
bottom of the clearing saw blade.
Data analysis
Autumn/Early Winter Treatments
A one-factor (initial treatment) analysis of variance (ANOVA) with initial cover as a covariate was
used to compare the infl uence of initial treatments on barberry cover at Clover Mill. All cover
values were arcsine transformed prior to analysis (Zar 1974). Tukey’s HSD test was used to test for
signifi cant diff erences among initial treatments. Diff erences were judged signifi cant at P < 0.05.
Winter Treatments
A two-factor (application method, month) ANOVA with initial cover as a covariate was used
to compare the infl uence of initial treatments on barberry cover at Bicentennial Pond. All cover
Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 185
values were arcsine transformed prior to analysis (Zar 1974). Tukey’s HSD test was used to test for
signifi cant diff erences among initial treatments. Diff erences were judged signifi cant at P < 0.05.
RESULTS
Autumn/Early Winter Treatments
At Clover Mill, initial barberry cover averaged 22 (±5) percent and total invasive cover averaged 43
(±8) percent (Table 1). While not measured, barberry was 2-3 feet tall prior to treatment. Initial
cover of both barberry (F=0.050, df=4, P=0.994) and total invasives (F=0.142, df=4, P=0.959) did
not diff er among treatments. Triclopyr applications using basal spray in December and wet-blade in
October were less eff ective for controlling barberry than other treatments (F=40.333, df=4, P=0.002),
averaging a 57 and 56 percent reduction, respectively. Control of all invasives averaged 72 percent
and did not diff er among treatments (F=0.360, df=4, P=0.827).
Winter Treatments
At Bicentennial Pond, initial barberry cover averaged 68 (±4) percent and total invasive cover averaged
69 (±4) percent (Table 2). While not measured, barberry was 3-4 feet tall prior to treatment. Initial
cover of both barberry and total invasives did not diff er between application methods (F=0.539,
df=1, P=0.473) or among month of application (F=0.947, df=2, P=0.407). e interaction of
application method by month of application was not signifi cant (F=0.223, df=2, P=0.803), and a
model without the interaction was used. Although both application methods reduced barberry cover,
Table 1.—Mean (standard error) initial (August 2008) and final (June 2009) cover (percent) of Japanese
barberry and invasives by treatment method at Clover Mill
Japanese barberry All invasives
Application Month Herbicide Aug08 Jun09 Aug08 Jun09
Foliar September glyphosate 16 (6) a†1 (1) b 28 (13) a 8 (4) a
Wet-blade October glyphosate 25 (8) a 1 (0) b 40 (20) a 8 (4) a
Wet-blade October triclopyr 19 (4) a 8 (0) a 48 (15) a 14 (2) a
Basal spray October triclopyr 28 (26) a 3 (3) b 47 (23) a 17 (13) a
Basal spray December triclopyr 20 (13) a 9 (4) a 45 (31) a 12 (5) a
†Column values followed by the same letter were not significantly different at P ≤ 0.05.
Table 2.—Mean (standard error) initial (November 2008) and final (October 2009) cover (percent) of
Japanese barberry and invasives by treatment method at Bicentennial Pond
Japanese barberry All invasives
Nov08 Jun09 Oct09 Nov08 Jun09 Oct09
Application method
Wetblade 66 (5) a†14 (3) a 1 (0) a 66 (5) a 18 (3) a 2 (0) a
Basal spray 71 (6) a 9 (3) b 1 (0) a 72 (6) a 10 (3) b 2 (1) a
Time of application
January 65 (8) a 9 (2) a 1 (0) a 66 (8) a 11 (3) a 1 (0) a
February 64 (5) a 16 (4) b 1 (1) a 64 (5) a 21 (5) b 3 (1) a
March 76 (5) a 9 (3) a 1 (0) a 77 (5) a 9 (3) a 1 (0) a
†Column values followed by the same letter were not significantly different at P ≤ 0.05.
Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 186
basal spray was more eff ective than the wet-blade at 88 vs. 79 percent, respectively (F=12.971, df=1,
P=0.002). Eff ectiveness varied among month of application (F=7.486, df=2, P=0.004). January and
March treatments reduced barberry cover more than February treatments at 89, 86, and 74 percent,
respectively.
Frequency (the number of points which had at least one barberry or invasive species) averaged 90
percent prior to treatment of both basal spray and wet-blade subplots at Bicentennial Pond. Inevitably,
some invasive plants were missed by initial treatments, especially small plants which were easily missed
in the dormant, leaf-off conditions of winter and those buried under snow. Frequency of points with
barberry averaged 37 and 55 percent after basal spray and wet-blade treatments, respectively.
Follow-up foliar spray applications of both glyphosate and triclopyr in late May after the initial winter
treatments were highly eff ective in reducing barberry cover by 98-99 percent of original cover (Table
2). ere was no diff erence between follow-up herbicides for controlling either barberry (F=0.738,
df=1, P=0.401) or total invasive species (F=0.167, df=1, P=0.688). After the follow-up treatments,
only 8 percent of points still had live barberry.
Costs
Labor costs (hours/acre) for initial treatments were correlated with pretreatment cover of invasive
species, (r2=0.51, P<0.001), but did not vary among application methods (F=2.005, df=2, P=0.152).
Pooling application methods, the estimated time for initial treatment was 1.2 + 0.10 hours/acre/10
percent cover. For example, if the invasive cover was 25 percent, then the treatment time would
be 1.2+ 0.1*(25/0.1)=3.7 hours/acre. It should be noted that these estimates do not include time
required for travel and preparation time prior to arriving at the fi eld.
e amount of herbicide used varied among application methods (F=25.205, df=2, P<0.001). Basal
spraying required approximately 4.4 times more herbicide per acre than wet-blade applications
(Fig. 1). Wet-blade application required 6.2 ounces/acre/10 percent cover, while basal and foliar
sprays required 27.3 ounces/acre/10 percent cover. Herbicide used (ounces/acre) was correlated
with pretreatment cover for both wet-blade (r2=0.40, chi-square=5.8, df=1, P=0.016) and spray
applications (r2=0.44, chi-square=10.2, df=1, P=0.001).
0
100
200
300
0% 20% 40% 60% 80% 100%
Triclopyr applied (ounces/acre)
Pretreatment cover of invasive species
Basal spray
Wetblade
Figure 1.—Amount of herbicide applied
(ounces per acre) by pretreatment cover
of invasive woody species, primarily
Japanese barberry, in central Connecticut.
Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 187
DISCUSSION
Our results indicated that a program to eff ectively control Japanese barberry intermingled with
other invasive species can be successful when initiated from October through March (Tables 1 and
2). Completing initial control during the dormant season can limit impact to nontarget species,
especially herbaceous plants that have lost their leaves.
Combined with earlier work that reported good initial control from April through September (Ward
et al. 2010), initial control of barberry can begin throughout the year using a variety of application
methods and herbicides, including nonchemical control (Ward and Williams 2011). erefore, the
choice of which application method and herbicide to use as the initial treatment can be tailored to the
unique attributes of a site and to the personnel available.
In our study, there was one period when treatment was not as eff ective. Both wet-blade and basal
spray application were less eff ective in February than in January or March (Table 2). Temperatures
were similar during treatment applications in January and February, ranging from 36-40 °F. ere
was little or no snow on the ground in January and March, but February treatments were applied
when there was 6-8 inches of snow on the ground. Because of the snow depth, herbicide application
may have been too high on stems to provide for adequate translocation to the root collar and below.
In addition, numerous stems off set from vertical were mostly or completely hidden from treatment
below the snow. We suggest dormant season treatments should not be attempted if snow depth is
more than 1 or 2 inches.
Although eff ective, we cannot recommend basal spray as a treatment to control barberry for a couple
of reasons. First, while basal applications can be an appropriate technique for invasive species with a
few large stems (Bowker and Stringer 2011, Lowe et al. 2007, Pergams and Norton 2006), the high
number of stems (often 20 or more) in a typical barberry clump (Ward et al. 2009), and the large
number of layered stems can require a very high volume of herbicide to be applied on a per acre
basis. Our estimate of the amount of herbicide needed (27.3 ounces/acre/10 percent cover) would
actually exceed the label maximum (256 ounces per acre) if pretreatment cover exceeded 94 percent.
Second, use of an oil (e.g., diesel) as a carrier may be restricted by state/local regulations because of
the potential to contaminate groundwater, while commercial basal oils (e.g., methylated seed oils) can
be quite expensive on a per acre basis when used in large volumes to treat a species with thousands of
stems such as barberry.
Using a clearing saw with a centrifugal herbicide applicator (the wet-blade) was as eff ective as
basal and foliar sprays (Tables 1 and 2) while requiring much less herbicide (Fig. 1), but also has
limitations. We noticed that there were strips where all cut stems were dead and other strips where
cut stems had new sprouts. We believe that the wet-blade could effi ciently transfer herbicide to the
blade for 30-45 minutes until the reservoir was about half full. A tank of gas for the clearing saw
would last for an hour or more. e period between refi lling the gas tank and refi lling the wet-
blade reservoir was when herbicide was not applied to cut stems. erefore, until the technology is
improved, we recommend pausing at 30 minute intervals to refi ll the herbicide reservoir and refuel
the saw when using wet-blade treatments. Use of the herbicide applicator may be a modifi cation not
approved by the manufacture and might invalidate the warranty. In addition, the wet-blade herbicide
applicator is quite expensive, costing $490 in 2010.
Proceedings of the 18th Central Hardwoods Forest Conference GTR-NRS-P-117 188
Other wet-blade studies have had mixed results. Wet-blade applications of diluted triclopyr did not
provide eff ective control of a variety of hardwoods in Pennsylvania (Gover et al. 2002). Mortality of
hazelnut (Corylus cornuta Marsh.), but not red maple (Acer rubrum L.), was increased using wet-blade
application of glyphosate in Ontario (Smith et al. 2009). Kirdar and Ertekin (2009) reported wet-
blade application of glyphosate provided excellent control of rhododendron (Rhododendron ponticum
L.) in Turkey.
None of the methods examined in this or earlier studies (Ward and Williams 2011, Ward et al.
2010) provided complete control of invasive species. Eight percent of sample points had live barberry;
many were small seedlings that would not survive more than a few years (Ehrenfeld 1999, Ward et
al. 2010). While these small plants contribute little to cover, they have the potential to grow and
re-infest the site. While it may be unrealistic to achieve complete, multi-year control, a more realistic
goal is to provide adequate control to allow the development of desired native herbaceous plants and
forest regeneration by periodically retreating the site to maintain invasives at low levels.
Because survival and growth of cut stems did not diff er between preleafout and postleafout initial
treatments (Ward et al. 2009), we recommend initial treatment during the dormant season when it
is easier to see tripping hazards and where barberry is rooted, which would otherwise be hidden by
foliage. Cooler temperatures during this period also increase comfort levels of operators wearing thick
clothing as protection from barberry spines. Follow-up treatments can be started in late May (Table
2) or delayed until later in summer to minimize over spray (herbicide drift) damage to nontarget
native plants (Ward et al. 2010). Biennial monitoring could be used to determine when additional
treatments might be required to maintain invasives at levels consistent with management objectives.
ACKNOWLEDGMENTS
We would like to thank the town of Mansfi eld, CT for fi nancial assistance and providing study
sites. Original funding to the town of Mansfi eld was provided by U.S. Department of Agriculture,
Department of Natural Resources Conservation Service, Wildlife Habitat Incentives Program, CT.
Technicians J.P. Barsky, M.R. Short, J.L. Bravo, and interns G. Picard, E. Cianciola, and C. Craig
assisted with plot establishment, treatments, and data collection.
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