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FOREST AND RANGE
EXPERIMENT STATION

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PNW-284 December 1976

‘4 HERBICIDES FOR CONTROL OF WESTERN SWORDFERN |
AND WESTERN BRACKEN

by

R. E. Stewart, Research Forester

- ABSTRACT

ce. Dicamba at 3 pounds acid equivalent per 100 gallons of carrier
a will control individual western swordfern plants when applied between

ey mid-May and late July. A mid-July foliage spray containing 1 to 3 |
iy pounds active ingredient per acre of asulam will produce good long-

a term control of western bracken without significantly affecting Douglas-

be firs or ponderosa pines.

a KEYWORDS: Herbicides, brush control, swordfern, Polystichwn munttum,
bracken fern, Pteridiwn aquilinum var. pubescens, Douglas-
fir, ponderosa pine, dicamba, asulam.

1 INTRODUCTION abundance of swordfern may affect

if mountain beaver populations. Recent
Western swordfern (Polystichun evidence shows that reclamation of red
A munitum) and western bracken (Ptertdiun alder (Alnus rubra Bong.) stands with
aquilinum var. pubescens) are common swordfern understories can be difficult
‘a herbaceous species on forest lands in (Dimock et al. 1976). Reduction or
western Oregon and Washington. The elimination of swordfern and bracken

: effect of competition from bracken on from conifer plantations may reduce

a conifer seedling establishment is well their desirability as habitat for tree-
h documented (Dimock 1964, McCulloch 1942, damaging animals and competition for

§ Staebler et al. 1954, Stewart 1975, light and soil moisture.

F Worthington 1955) but is unknown for

| swordfern. Swordfern is known to be a Western swordfern is found on forest
4 major winter food for a tree-damaging lands in limited geographic areas and
W mammal, mountain beaver (Aplodontia has not been considered a serious

iJ rufa) (Voth 1968). This suggests that competitor to seedlings. Nothing was

ey
ik

OREST SERVICE -US. DEPARTMENT OF AGRICULTURE - PORTLAND, OREGON |

known about its control. In contrast, - Comparisons of herbicide effectiveness
varieties of bracken are a serious were based on analysis of percentage of
problem in pastures and on forest plants killed for western swordfern and
lands throughout the world. Although percentage of ground cover for western
information on response of western bracken.
bracken to herbicides was available
(Fechtig 1968, Fechtig and Furtick -
1965, Homesley and Furtick 1968, AISI) SUA
Robocker 1971), satisfactory treatments During the 1970 growing season, four
for controlling this species had not been herbicides were tested as foliage 3
been developed. sprays on western swordfern near Sitkum, —
re i ; . é Oregon. Each treatment was applied in
Beginning in 1970, a series of studies a water carrier by knapsack sprayer to
were installed to develop herbicidal drip point on 10 individual plants. 4
treatments to control western swordfern Herbicides were applied as early foliar
and western bracken. Since swordfern sprays on May 26, when fronds were at
is likely to require control only in a mid- to late-hook stage, or as mid-
localized areas, efforts were directed ‘summer sprays on July 28, when fronds
toward developing individual plant were mature and sori were yellow to
treatments. Bracken is a more widespread rust colored. Results observed in
problem requiring treatments suitable September 1971, 13 to 15 months after
for broadcast application. : treatment, are shown in table 1.
All studies were installed as com- Swordfern was equally susceptible to
pletely randomized experiments and the sprays applied in late spring and mid-
results analyzed by analysis of variance. summer, but there was a significant

Table 1--Effects of herbicides as early foltar or midsummer sprays on

western swordfern, 13 to 15 months after treatment

Early foliar spray

Midsummer spray

No. of
fronds Average Average
a ats Concen- Plants
Herbicide ; : per frond . frond
tration| killed eters Reaene killed heiehe

plant
1b asin! Percent Inches Percent Inches
Untreated 0 0 47 26 0 47 26
Picloram 1 0 24 18 0 Soe US)
2 40 24 17 20 29 21
Dicamba 4 80 20 25 30 ZA 17
8 80. 36 20 90 6 11
Dichlobenil 4 20 15 23 30 16 23
8 60 10 18 50 18 23
Bromacil 12 100 0 0 90 IL7/ 119
1/

— Pounds of active ingredient per 100 gallons of water.

difference in plant kill obtained with
the four herbicides. Of the herbicides
and rates tested, dicamba at a maximum
of 4 pounds active ingredient per 100
gallons (lb aihg) (fig. 1) and bromacil
at 12 1b applied as early foliar sprays
were the most effective. The most
effective concentration of picloram or approximately 3 1b aihg. However,
dichlobenil was not attained in this dicamba is somewhat more effective
study. than bromacil at this concentration.
The results also suggest that the
oil-soluble formulation of dicamba
applied in diesel oil is better than
the water-soluble formulation applied
in water at equal concentrations--

1 pound acid equivalent per 100 gallons
(1b aehg).

All treatments reduced the vigor of
surviving plants compared with
untreated swordfern. Averaged over
all dosages, bromacil produced better
plant kill than dicamba. As shown in
figure 2, the minimum effective con-
centration of both herbicides is

Both the water-soluble and oil-
soluble formulations of dicamba are
registered for use as high volume
ground-applied sprays on forest land;
bromacil is not. Therefore, dicamba
is preferred to bromacil as an early
foliar application for control of
western swordfern.

Dicamba and bromacil are soil- and
foliage-active and may severely damage
conifers, so sprays should be carefully
applied on individual swordfern plants
to avoid drift onto adjacent conifers.
For site preparation, dicamba should
be applied the year before planting.

Figure 1.--Western swordfern plant
killed by an early foliar spray of
3 pounds acid equivalent of dicamba
per 100 gallons of water.

A second study was installed to find

the minimum effective concentration of
dicamba and bromacil. During May 1972,
10 individual western swordfern plants
were sprayed to drip point with each
treatment when new fronds were at the
early- to late-hook stage. Most sprays
were applied in water carriers. How-
ever, old fronds are also present at
this stage, and these seem more resist-
ant than new fronds to herbicides
applied in water carriers. Therefore,
an 0il-soluble dicamba formulation
applied in a diesel oil carrier was
also tested. Results observed in

July 1973, 14 months after treatment,
are shown in table 2.

WESTERN BRACKEN

During the 1970 growing season, the
four herbicides tested on western
swordfern were also applied as foliage
sprays on western bracken near Blodgett,
Oregon. Each treatment was applied by
knapsack sprayer in a water carrier
at a volume equivalent to 200 gallons
per acre to ten 1/1,000-acre circular
plots. Herbicides were tested as early
foliar sprays on June 15, when fronds
were almost fully expanded, and as
midsummer sprays on August 10, when
fronds were mature and sori were green.

100

40

PLANTS KILLED (Percent)

20

Table 2--Effects of vartous concentrations of dteamba and bromactl

as early foliar sprays on western swordfern, 14 months
after treatment

Herbicide and Concen- Plants Moe oe enonds AvcL age
carrier tration killed Ble ane prong
live plant height

1b aihg?/ Percent Inches

Untreated 0 0) 50 36
Dicamba (oil) 1 10 16 20
(water) 1 0 34 29

(water) 2 40 14 21

(water) 3 90 6 22
Bromacil (water) 1 20 29 25
(water) 2 50 12 17

(water) 3 70 22 20

(water) 6 70 8 18

£ Pounds of active ingredient per 100 gallons of carrier.

During September 1971, 13 to 15
months after treatment, percent bracken
cover and frond height and density were
estimated on each plot. Height and
density were obtained by measuring the
average height and number of fronds in
four systematically located 1-foot-
square subsamples in each plot. The
results of treatment are shown in
table 3.

Dicamba was by far the most effective
herbicide tested for reducing bracken
cover, and 4 1b ai per acre was as effec-
tive as 8 lb. Early foliar sprays were
less effective than midsummer sprays.
This finding agrees with other studies,
although Fechtig (1968) and Homesley and
Furtick (1968) indicate that both
picloram and dichlobenil can produce
somewhat better control. Tests in Great
Britain show that 4 1b ai per acre of
dicamba can control bracken for up to
four growing seasons on infertile sites
but only for two seasons on fertile,

2 3 4 5

Herbicide concentration (1b aihg)

Figure 2.--Response of western sword- moist sites (Forestry Commission 1969).
fern to different concentrations of In the present study, none of the

dicamba and bromacil.

Table 3--Effects of herbicides as early foliar or midsummer sprays on western

bracken, 13 to 15 months after treatment

Herbicide

1b ai/Al/ Percent No./ft2
Untreated 0 87 1.8
Picloram 1 70 10
2 48 9
Dicamba 4 4 5h)
8 2 a
Dichlobenil 4 74 1.3
8 86 1.6
Bromacil 12 76 1.6

Pounds of active ingredient per acre.

herbicides adequately controlled western
bracken beyond the second season.

Dicamba is somewhat persistent, soil
active, and can severely damage conifers
(Ryker 1970, Stewart 1974). Asulam, a
herbicide developed in Great Britain,
has produced excellent control of other
varieties of bracken fern at 4 to 8 lb
ai per acre without damaging certain

| Early foliar spray | Early foliar spray spray

species of conifers (Holroyd et al. 1970,

Martin et al. 1972, Soper 1972, Wasmuth
1973). Its effects on Douglas-fir
(Pseudotsuga menztesit) and western
bracken were unknown; therefore, a test
was installed near Harlan, Oregon, to
compare effectiveness of asulam and
dicamba for control of western bracken.

Each treatment was applied to three
1/100-acre-square plots of western
bracken in mid-July of 1972 after com-
plete frond elongation. All sprays
were applied with 0.2 percent surfactant

Midsummer spray

Average Average
stem stem
height height

Inches Percent No./ft% Inches
43 87 1.8 43
50 30 9 43
49 16 S7 34
43 24 8 38
2 2 0 0
43 83 Me U7 48
48 90 USS 47
46 60 iL S74 53

in water at a volume equivalent to 200
gallons per acre. Bracken cover and
stem density and height were observed in
July--12, 24, and 36 months after
treatment. Stem density and height

were measured in five 1-foot-square sub-
samples systematically located along

the diagonals in each plot. Results

of the first and last examinations are
shown in table 4. Change in bracken
cover during the 3 years after treat-
ment is shown in figure 3.

Asulam was more effective than
dicamba in reducing bracken cover dur-
ing the 3-year study. Effects of
dicamba were evident by the end of the
first growing season, 2 months after
treatment. In contrast, asulam did
not affect existing fronds but prevented
emergence of new fronds the next year.
Sprays containing 1 1b ai per acre of

Table 4--Effect of dicanba and asulam as midsummer foltage sprays

on western bracken

12 | 12 months after treatment | after | 12 months after treatment |

Average
Dosage Cover Stems stem
height

36 months after treatment

Average
stem
height

Herbicide

1b nee Percent No./ft2 Feet Percent No./ft2 Feet
Untreated 0 90 1.33 5.1 88 1.07 bbe 7
Dicamba 4 57 1.20 2.4 73 1.20 4.0
Asulam 1 WW 5 Ales 236 7b tf -40 3.8
2 8 .10 BASS 12 .08 2.1
3 5 03 2.0 v 120 25
1/

— Pounds of active ingredient per acre.

asulam were almost as effective as
sprays containing 2 or 3 1b. Bracken
treated with dicamba recovered sub-
stantially by the 3d year after spraying
(fig. 4). In contrast, recovery was
very slow after treatment with asulan,
even at the lowest dosage (fig. 5). As
expected, Douglas-firs present on the
4 |b of dicamba plots at the time of treatments were
per acre severely damaged by dicamba (fig. 6);
asulam did not damage trees at dosages
up €o! 5" 1b) ale persacrem (tage,

Untreated

Effectiveness of asulam for control-
ling western bracken was confirmed in
2» a small test installed during June 1973
Pcie on the Entiat Ranger District of the
_e 1 Ib of asulam Wenatchee National Forest in the
ie per acre Wenatchee Mountains of central Washington.

Three 1/100-acre plots each were sprayed

“2 z with 1 or 3 1b ai per acre of asulam

lb of, asulam ,per acre

WESTERN BRACKEN COVER (Percent)

with 0.2-percent surfactant in water
0 12 24 36 48 : :
at a carrier volume equivalent to 200
TIME AFTER TREATMENT (Months) gallons per acre. Results obtained 12
months after treatment are shown in
Figure 3.--Western bracken cover on table 5.
untreated plots and on plots
treated with dicamba or asulam. As in tests in western Oregon, asulam

produced good control of western bracken
in central Washington. However, a higher

_
nat ease
Figure 4.--Bracken fern recovered Figure 5.--Bracken fern recovered very

substantially by the 3d year after slowly after treatment with asulam.
spraying with 4 lb aehg of dicamba.

Figure 7.--Asulam did not damage
Douglas-firs such as these two
3-foot-tall trees.

Figure 6.--Dicamba severely
damaged Douglas-firs such
as this 3-foot-tall tree.

Table 5--Effect of asulam applted as an early foliar
spray on western bracken tn the Wenatchee
Mountatns, 12 months after treatment.

Treatment

1b ai/al/ Percent No./ft2 Feet

Untreated 0 53 53 1.8
Asulam 1 37 -60 eA
3 10 07 1.8

1/

— Pounds of active ingredient per acre.

dosage was required to control the
shorter, more open bracken on these sites
than to control the taller, more dense
bracken in western Oregon. Perhaps
western bracken growing on drier sites

is more resistant to asulam or may have

a thicker waxy cuticle that reduces
uptake of herbicides applied in water
carriers.

To better determine the suitability
of asulam for conifer release, 10 seed-
lings each of Douglas-fir and ponderosa
pine (Pinus ponderosa) were sprayed to
drip point with 1/2 1b aihg of asulam
in a water carrier. Treatments were
applied on June 19 at the beginning of
active growth, on July 13 as terminal
growth stopped but while new growth was
succulent, and on August 14 after buds
were set and new growth was woody. The
concentration approximated a 2-1b-ai-
per-acre application rate based on
experience with phenoxy herbicides
(Gratkowski 1961). Defoliation and
topkill 2 years after spraying and
average annual height growth before and
after spraying are shown in table 6.

The data show that asulam did not
affect height growth of either Douglas-fir
or ponderosa pine after adjusting for
differences in individual tree growth
before treatment using covariance analy-
sis. However, variation was considerable,

and some small growth reduction may be
possible.

Douglas-firs seemed more sensitive to
asulam than ponderosa pines. Visible
damage was slight in both species, but
susceptibility was highest on June 19
during the period of active growth. This
suggests that Douglas-fir and ponderosa
pine seedlings can be safely released if
sprays are applied after new growth
ceases and terminal buds have set. This
conclusion has been verified in a series
of aerial spray tests.!

CONCLUSIONS

Western swordfern can be adequately
controlled with sprays containing 3 1b
aehg of dicamba applied in water to drip
point on individual plants. Sprays can
be applied anytime between the midhook
and fully elongated frond stages,
approximately mid-May to late July.
Damage to conifers can be prevented if
sprays are applied the year before
planting or carefully directed away from
young conifers on the site.

Western bracken can be controlled for
at least 3 years with 1 to 3 1b ai per

1Unpublished data on file at the Forestry
Sciences Laboratory, Pacific Northwest Forest
and Range Experiment Station, Corvallis, Oreg.

Table 6--Effect of asulan on Douglas-fir and ponderosa pine seedlings

2 years after treatment

Species
and Initial
application height
ee Before
treatment—

-- freee Meters

Douglas-fir:

Untreated 1.68 0.55

June 19 1.64 44

July 13 1.78 58

August 14 15 TAs) 56
Ponderosa pine:

Untreated 1G 7/5) .59

June 19 2.03 58

July 13 WA? .64

August 14 1.96 74

1/

Average annual
height growth

treatment—

Defoliation | Topkill

After

2/

----- Percent
0.73 0 0
59 12 3
73 2 0
60 10 0
98 5 0
86 14 0
87 5 0
eOiti 5 0

=, Total growth during the 2 years before treatment.

2/

acre of asulam applied after frond
emergence, but some recovery of bracken
may occur after treatment with 1 1b of
asulam. Sprays applied in mid-July or
August produced good bracken control
without damaging Douglas-firs or ponder-
osa pines. Asulam is registered for
use on Christmas tree plantations, and
registration for use in site preparation
and conifer release on forest lands is
expected soon.

Experience suggests that results from
small plot tests such as those reported
here often closely agree with results
from operational use under similar
conditions. However, as with any new
technology, it is wise to begin use of
new herbicides on a small scale to
establish local experience. This pre-
liminary step can save time and money

Total growth during the 2 years after treatment.

later. Further, sharing your experience
with others can prevent adoption of
faulty technology and hasten adoption
of useful technology.

METRIC CONVERSIONS

1 pound = 0.45 kilogram

1 inch = 2.54 centimeters
1 gallon = 3.78 liters

1 acre = 0.40 hectare

1 foot = 0.30 meter

LITERATURE CITED

Dimock, Edward J., II.

1964. Supplemental treatments to aid
planted Douglas-fir in dense bracken
fern. USDA For. Serv. Res. Note
PNW-11, 10 p. Pac. Northwest For.
and Range Exp. Stn., Portland, Oreg.

Dimock, Edward J., II, Enoch Bell, and.
Robert M. Randall.
1976. Converting brush and hardwoods
to conifers on high sites in western
Washington and Oregon. USDA For.

Serv. Res.) Pap. .PNW=213))) di6i pe il lus).

Pac. Northwest For. and Range Exp.
Stn., Portland, Oreg.
Fechtiis, A.) D).

1968. Chemical control of bracken
fern (Ptertdtum aquilinum L.)
in western Oregon. Res. Prog. Rep.
West. Soc. Weed Sci. 1968:5-6.

Fechtig, A. D., and W. R. Furtick.

1965. Chemical control of bracken
fern (Pterts aquilina L.) in
western Oregon. Res. Prog. Rep.
West. Weed Control Conf. 1965:17-18.

Forestry Commission.

1969. Bracken control with dicamba.
Rep. For. Res. For. Comm., London
1968/69. 1969:76-77.

Gratkowski, H.

1961. Toxicity of herbicides on three
northwestern conifers. USDA For.
Serv. Pac. Northwest For. and Range

Exp. stn. Res. Pap... 4238 24% pn fast ibust.

Portland, Oreg.
Holroyd, J., C. Parker, and A. Rowlands.

1970. Asulam for the control of
bracken (Ptertdtum aqutlinum (L.)
Kuhn). Proc. 10th Br. Weed Control
Conf. 1970:371-376

Homesley, W. B., and W. R. Furtick.

1968. Bracken fern date of applica-
tion experiment. Res. Prog. Rep.
West. Soc. Weed Sci. 1968:7-9.

McCulloch, W. F.

1942. The role of bracken fern in
Douglas-fir regeneration. Ecology
23:484-485.

Martin, D. J., G. H. Williams, and
J. C. Raymond.

1972. The effect of asulam on
bracken frond number, rhizome
viability, and frond carbohydrate
ratios. Proc. 11th Br. Weed
Control Conf. 1972:331-334.

10

Robocker, W. C.
1971. Herbicidal suppression of bracken
and effects on forage production.
Weed Sci. 19:538-541.
Ryker, R. A.
1970. Effects of dicamba and picloram
on some northern Idaho shrubs and

trees. USDA For. Serv. Res. Note
' INT-114, 6 p. Intermt. For. and
Range Exp. Stn., Ogden, Utah.
Soper D.
1972. Review of bracken control experi-

ments with asulam. Proc. llth. Br.
Weed Control Conf. 1972:24-31.
Staebler, G. R., P. Lauterbach, and
A. W. Moore.

1954. Effect of animal damage on a
young coniferous plantation in
southwest Washington. J. For. 52:
730-733.

Stewart, R. E:

1974. Foliage sprays for site prepara-
tion and release from six coastal
brush species. USDA For. Serv. Res.
Paps "PNWo 72) Ss pe lus em bacr
Northwest For. and Range Exp. Stn.,
Portland, Oreg.

Stewart, R. E.

1975. Allelopathic potential of
western bracken. J. Chem. Ecol.
1(2):161-169, illus.

Voth, pr .gH.

1968. Food habits of the Pacific
mountain beaver, Aplodontia rufa
pactfitca Merriam. Ph. D. thesis.
Oreg. State Univ., Corvallis. 263 p.

Wasmuth, A. G.

1973. The release of Pinus radtata
from bracken with asulam. N.Z. J.
For. 18:279-284.

Worthington, N. P.

1955. A comparison of conifers planted
on the Hemlock Experimental Forest.
USDA For. Serv. Pac. Northwest For.
and Range Exp. Stn. Res. Note 111,

5 p. Portland, Oreg.

PESTICIDE PRECAUTIONARY STATEMENT

Pesticides used improperly can be injurious to man, animals, and plants. Follow the
directions and heed all precautions on the labels.

Store pesticides in original containers under lock and key--out of the reach of children
and animals--and away from food and feed.

Apply pesticides so that they do not endanger humans, livestock, crops, beneficial
insects, fish, and wildlife. Do not apply pesticides when there is danger of drift, when honey
bees or other pollinating insects are visiting plants, or in ways that may contaminate water
or leave illegal residues.

Avoid prolonged inhalation of pesticide sprays or dusts; wear protective clothing and
equipment if specified on the container.

If your hands become contaminated with a pesticide, do not eat or drink until you have
washed. In case a pesticide is swallowed or gets in the eyes, follow the first-aid treatment
given on the label, and get prompt medical attention. If a pesticide is spilled on your skin
or clothing, remove clothing immediately and wash skin thoroughly.

Do not clean spray equipment or dump excess spray material near ponds, streams, or
wells. Because it is difficult to remove all traces of herbicides from equipment, do not use
the same equipment for insecticides or fungicides that you use for herbicides.

Dispose of empty pesticide containers promptly. Have them buried at a sanitary land-fill
dump, or crush and bury them in a level, isolated place.

NOTE: Some States have restrictions on the use of certain pesticides. Check your State and
local regulations. Also, because registrations of pesticides are under constant review by the
Federal Environmental Protection Agency, consult your county agricultural agent or State
extension specialist to be sure the intended use is still registered.

FOLLOW THE LAGEL

@S. DEPARTMENT OF AGRICULTURE

iit

The mission of the PACIFIC NORTHWEST FOREST
AND RANGE EXPERIMENT STATION is to provide the
knowledge, technology, and alternatives for present and
future protection, management, and use of forest, range, and
related environments.

Within this overall mission, the Station conducts and
stimulates research to facilitate and to accelerate progress
toward the following goals:

1. Providing safe and efficient technology for inventory,
protection, and use of resources.

2. Developing and evaluating alternative methods and
levels of resource management.

3. Achieving optimum sustained resource productivity

consistent with maintaining a high quality forest —

environment.

The area of research encompasses Oregon, Washington,
Alaska, and, in some cases, California, Hawaii, the Western
States, and the Nation. Results of the research are made
available promptly. Project headquarters are at:

Fairbanks, Alaska Portland, Oregon
Juneau, Alaska Olympia, Washington
Bend, Oregon Seattle, Washington
Corvallis, Oregon Wenatchee, Washington

La Grande, Oregon

Mailing address: Pacific Northwest Forest and Range
Experiment Station
P.O. Box 3141
Portland, Oregon 97208

GPO 997-606

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