HERBICIDES TO AID ESTABLISHMENT
OF FOURWING SALTBUSH
Joseph L. Petersen
Darrell N. Ueckert
Matthew W. Wagner
of this study was to identify herbicides effective for selective control of competing vegetation in fourwing saltbush
plantings.
ABSTRACT
Failures in attempts to establish fourwing saltbush
(Atriplex canescens) are often attributed to interference
from weeds. Field experiments were conducted in western
Texas to evaluate preemergence and postemergence applications of selected herbicides for we~d control in fourwing
saltbush plantings. Sprays ofmetolachlor at 2.0 kg a.i.lha
and alachlor at 2.5 kg/ha appeared promising as preemergence treatments. Acifluorfen at 0.56 kglha and clopyralid
at 0.28 kg/ha effectively controlled broadleafed weeds, and
fluazifop-P at 0.21 kg/ha effectively controlled grasses
while causing no or only slight injury to fourwing saltbush
plants that were 1 month to 2 years old. Postemergence
herbicides appear more practical than preemergence herbicides in arid and semiarid areas where fourwing saltbush
is utilized.
MATERIALS AND METHODS
The study was conducted on an Angelo clay loam
(fine, mixed, thermic Torrertic Calciustolls) at the Texas
A&M University Agricultural Research and Extension
Center, 8 km northwest of San Angelo in the southern
Rolling Plains resource area. Soil pH was 7.8 and organic
matter content was 1.2 percent .. Elevation is 580 m and
mean annual precipitation is 47 em. The most predictable
and abundant periods of rainfall are April-June and
September-October.
Preemergence Herbicide Experiments
INTRODUCTION
Selected preemergence herbicide treatments were
evaluated in three experiments. Seedbeds were disked
twice and packed before planting. About 800 dewinged
fourwing saltbush seeds (4 g) from a commercial source
(harvested in western Texas) were hand planted 1.3 em
deep in each of two 120-cm rows in 2- by 2-m plots separated by 1.2-m borders. Germination of the seed on moist
blotter paper in a controlled environment was 22 percent.
Herbicide treatments included trifluralin [2,6-dinitroN ,N-dipropyl-4-(trifluoromethyl)benzenamine] at 0.8 kg
a.i .lha, oryzalin [4-( di propyl amino)-3,5-dini trobenzenesulfonamide] at 1.1 kg/ha, ethalfluralin [N-ethyl-N-(2methyl-2-propenyl)-2, 6-dinitro-4-(trifl uoromethyl)benzenamine] at 1.9 kg/ha, metolachlor [2-chloro-N-(2ethyl-6-methyl phenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.0 kg/ha, and alachlor [2-chloro-N-(2,6diethylphenyl)-N-(methoxymethyl)acetamide] at
2.8 kg/ha.
Treatments were applied in separate experiments on
April27, 1987, September 15, 1987, and May 13, 1988.
Other treatments included hand-weeding and untreated
checks. Herbicides were applied in water at a total volume of 1.9 Uplot using hand-held sprayers. Trifluralin
was incorporated 3 to 5 em deep with garden rakes immediately after application, just prior to planting fourwing
saltbush seed. All other herbicides were applied immediately after seeding, without incorporation. The experiments were arranged as randomized complete blocks with
four replications. Soil water contents were maintained
at field capacity by frequent irrigation with garden sprinklers to assure seed germination, emergence, and establishment offourwing saltbush. The study sites were
fenced to eliminate rodents, lagomorphs, and livestock.
Fourwing saltbush (Atriplex canescens) is used extensively for rangeland seeding because of its wide range
of adaptation to edaphic and climatic conditions and its
potential to produce nutritious forage for livestock and
wildlife, particularly during winter (Plummer and others
1966; Petersen and others 1987). However, success in
establishing the shrub by seeding or transplanting
seedlings has been highly variable. Failures have been
attributed to poor seedbed preparation, poor seed quality,
inadequate soil moisture, grazing, and excessive competition from associated plants (Springfield 1970; Nord and
others 1971; Aldon 1972; Petersen and others 1986).
Plant competition is most often the primary factor
limiting establishment offourwing saltbush plantings
(Giunta and others 1975; VanEpps and McKell 1977,
1983; Geist and Edgerton 1984; Petersen and others
1986). Selective weed control practices are often needed
to enhance and hasten shrub establishment and return
the investment in seed, seedbed preparation, fencing,
and deferment. Various weed control strategies have
increased the survival and growth of tree plantings in
semiarid regions (Felker and others 1986). The objective
Paper presented at the Symposium on Cheatgrass Invasion, Shrub DieOff, and Other Aspects of Shrub Biology and Management, Las Vegas, NV,
April 5-7, 1989.
Joseph L. Petersen and Darrell N. Ueckert are Research Associate and
Range Ecologist, respectively, Texas Agricultural Experiment Station,
7887 N. Hwy. 87, San Angelo, TX 76901. Matthew W. Wagner is Biologist
II, Texas Parks and Wildlife Department, 4200 Smith School Road, Austin,
TX 78744.
305
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
Phytotoxicity of the herbicides to fourwing saltbush was
quantified by counting the live seedlings 15 and 90 days
after treatment (DAT) and by measuring seedling heights
90 DAT. Canopy cover (percent) of grasses and broadleafedweeds was visually estimated in five 0.1-m2 randomly located quadrats in each plot 90 DAT. Grasses
and broadleafed weeds were then harvested at ground
level and dried to a constant weight at 50 °C for estimates
of standing crop.
Phytotoxicity of the herbicides to fourwing saltbush
plants was estimated 15 and 90 DAT by visually ranking
percent necrosis in each plot (0 percent = no visible injury,
100 percent = no live tissue visible). Efficacy of the treatments for weed control was estimated 90 DAT by visually
estimating weed canopy cover from five 0.1-m2 randomly
located quadrats in each plot. Grasses and broadleafed
weeds in the quadrats were then harvested at ground
level and dried to a constant weight at 50 oc for estimates
of standing crop.
The data were subjected to analyses of variance. Transformations of percentage data did not affect data interpretation, so actual values are presented. Results from the
April 1987 and May 1988 experiments with preemergence
herbicides were similar, thus the data were pooled. Means
were separated by Duncan's multiple range test (P = 0.05)
where appropriate.
Postemergence Herbicide
Experiments
Field experiments were established to evaluate the
effects of selected postemergence herbicides on fourwing
saltbush seedlings. Plots were 3 by 3m and separated
by 1.2-m borders. Plots were rototilled and packed just
prior to planting seed and transplanting seedlings. Four
age classes offourwing saltbush plants occurred in each
plot when treatments were applied. These included:
(1) 1-month-old seedlings, hand planted at 8 g/2.4-m
row, 1.3 em deep, about 6 weeks prior to treatment. The
number of seedlings present at time of treatment ranged
from 12 to 80/plot; (2) 4-month-old seedlings (seven/plot),
transplanted on 38-cm centers 1 month prior to treatment; (3) 9-month-old seedlings (seven/plot), transplanted
on 38-cm centers 1 month prior to treatment; and (4) 2year-old, stem-cut seedlings (five/plot), transplanted on
61-cm centers 6 months before treatment. One row of
each plant age class was included in each plot.
Seeds used for the first three age classes were purchased from a commercial source harvested in western
Texas. The stem-cut seedlings were from mature plants
of an accession from Texon, TX, growing in a nursery at
the Research Center. The plots were frequently irrigated
as discussed earlier.
Herbicide treatments applied postemergence to the
weeds June 16, 1988 included acifluorfen {5-[2-chloro-4(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} at 0.56 kg
a.i .lha, metsulfuron {2-[[[[( 4-methoxy-6-methyl-1,3,5triazin-2yl)amino]carbonyl]amino]sulfonyl]benzoic
acid} at 0.04 kg/ha, sulfometuron {2-[[[[(4,6-dimethyl-2pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid}
at 0.05 kglha, fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2pyridinyl]oxy]phenoxy]propanoic acid} at 0.21 kg/ha, and
clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) at 0.28
kg/ha. Herbicide treatments applied on October 4, 1988
were the same as above except that metsulfuron and sulfometuron were applied' at 0.02 kg/ha based on results
from the first experiment. Broadleafed and grass weeds
were actively growing and varied phenologically from the
two-leaf stage to flowering at time of herbicide application
in both experiments.
Herbicides were applied as broadcast sprays in water
at a total volume of 1.9 Uplot with hand-held sprayers.
A nonionic surfactant (trimethylnonylpolyethoxyethanol)
was included at 0.13 percent (v/v) with acifluorfen and
at 0.25 percent (v/v) with all other herbicides. Other
treatments in both experiments included hand weeding
and untreated checks. The experiments were arranged
as randomized complete blocks with three replications.
Plots were fenced to exclude herbivores.
RESUL~PREEMERGENCE
HERBICIDES
Preemergence applications of metolachlor and alachlor
had little effect on emergence or growth of fourwing
saltbush seedlings. Shrub seedling densities in plots
treated with metolachlor or alachlor were similar to
those in hand-weeded plots after 90 days (table 1).
However, shrub seedling densities were significantly
lower (P = 0.05) in plots treated with trifluralin, oryzalin,
and ethalfluralin than in hand-weeded plots after 90
days. Seedling emergence and establishment were much
lower following autumn seeding compared to spring seeding, but the responses to autumn herbicide applications
were generally similar to those observed for spring
treatments.
The preemergence herbicides did not affect saltbush
seedling heights compared to heights of seedlings in handweeded plots (table 1). The high mortality of saltbush
seedlings during the first 3 months after planting in wellprepared seedbeds with hand weeding and frequent irrigation indicated that poor stand establishment in these
experiments was partly related to poor seed quality, low
inherent vigor of seedlings, or both.
Table 1-Fourwing saltbush seedling densities (No./2.4-m row) 30
and 90 days (d) and heights (mm) 90 days after spring or
autumn applications of selected preemergence herbicides
near San Angelo, TX 1
Average seedling
densities
Average seedling
Autumn
height at 90 d
Treatment
S~ring 2
Rate 30d 90d 30d 90d S~ring Autumn
Herbicide
kglha --- -No./2.4-m row---- - - - - mm - - - - Trifluralin
Oryzalin
Ethalfluralin
Metolachlor
Alachlor
Hand weeded
None
0.8
1.1
1.9
2.0
2.8
20b
38ab
33b
49ab
39ab
66a
40ab
7b
2c
1c
12b
7bc 2c
12b
9bc 2c
19ab 17b
Sbc
17ab 12b Sbc
29a 14b
7ab
12b 27a 11a
44b
74ab
34b
64ab
66ab
71ab
96a
4
17
13
13
14
18
19
Means within a column followed by similar lower case letters or without
letters are not significantly different (P= 0.05).
2Average of two experiments.
1
306
Weeds in the experimental area included common
purslane (Portulaca oleracea), Dakota verbena (Verbena
bipinnatifida), spear globemallow (Sphaeralcea hastulata), common devilsclaws (Martynia louisianica), western
ragweed (Ambrosia psilostachya), kleingrass (Panicum
coloratum), and common oats (Avena sativa). All herbicides applied in the spring experiments reduced weedy
plant cover compared to that on untreated plots (table 2).
Canopy cover of weeds was significantly less on alachlortreated plots compared to plots treated with ethalfluralin,
but there were no other differences among the herbicide
treatments. All herbicides except ethalfluralin reduced
the standing crop of grasses compared to untreated plots
but differences in broadleafed weed standing crop among
the treatments were not significant (table 2) due to high
within-treatment variation caused by the "patchy" distribution of weeds. Canopy cover and standing crop of
annual weeds were considerably less in the autumn experiment compared to the spring experiment (table 2).
Weed canopy cover and standing crop did not differ significantly with treatment in the autumn experiment.
Most of the preemergence herbicides initially suppressed weed establishment and growth, but rapid weed
emergence and growth began in most plots after about
60 days in all experiments. Rates of application used
were those recommended for medium-textured soils.
Weed emergence and growth after 60 days probably reflect the short residual of these preemergence herbicides.
Higher rates of application do not appear feasible because
of the tendency of most of the herbicides to reduce the
establishment, growth, or both, of saltbush seedlings
(table 1).
RESUL~POSTEMERGENCE
HERBICIDES
One-Month-Old Seedlings-Mid-June applications of
metsulfuron at 0.04 kg/ha and sulfometuron at 0.05 kg/ha
killed 1-month-old seedlings offourwing saltbush within
90 DAT (table 3). Visual estimates of injury caused by the
other treatments were similar to those of untreated and
hand-weeded plots at 90 DAT, although acifluorfen and
clopyralid appeared to cause slight injury to 1-month-old
seedlings.
Application rates of metsulfuron and sulfometuron were
reduced to 0.02 kglha in the second experiment (October
1988), but visual estimates of injury to 1-month-old seedlings at 90 DAT were still high (100 and 83 percent for
metsulfuron and sulfometuron, respectively) (table 4).
Initial injury caused by acifluorfen applied at 0.56 kg/ha
was moderate (43 percent), but seedlings had generally
recovered after 90 days. Clopyralid applied at 0.28 kg/ha
in October caused moderate injury (40 percent), whereas
fluazifop-P applied at 0.21 kglha caused no apparent phytotoxicity to 1-month-old seedlings (table 4).
Four· and 9-Month-Old Seedlings-Four- and
9-month-old fourwing saltbush plants appeared vigorous
when herbicides were applied. Injury to 4-month-old
seedlings was near 100 percent 90 days after June applications ofmetsulfuron and sulfometuron applied at 0.04
and 0.05 kg/ha, respectively (table 3). Phytotoxicity
symptoms resulting from June applications of the other
herbicides were slight to moderate after 90 days. Ninemonth-old seedlings were also killed by metsulfuron.
Sulfometuron was less toxic than metsulfuron, as evidenced by decreased phytotoxicity as seedling age
increased. Clopyralid sprays applied in June caused
moderate injury to 9-month-old seedlings (table 3).
Four- and 9-month-old seedlings were more tolerant of
the lower rates (0.02 kglha) ofmetsulfuron and sulfometuron applied in October (table 4), but injury by the lower
rate ofmetsulfuron was still unacceptable (63 percent).
The 4- and 9-month-old shrub seedlings were generally
uninjured or only slightly injured by sprays of acifluorfen,
fluazifop-P, or clopyralid applied in October.
Table 2-Canopy cover (percent} and standing crop
(g/m 2} of competing vegetation 90 days after
spring or autumn applications of selected
preemergence herbicides to plantings of
fourwing saltbush near San Angelo, TX 1
Treatment
Herbicide
Rate
kg!ha
Canopy Weed standing cro~
Broadleaf Grasses
cover
Percent
- - - - - - glmZ - - - - - -
Spring planting
Trifluralin
0.8
Oryzalin
1.1
Ethalfluralin 1_.9
Metolachlor 2.0
Alachlor
2.8
None
26bc
25bc
28b
22bc
15c
58a
Two-Year-Old Seedlings-Metsulfuron applied in
mid June at 0.04 kglha caused almost total (94 percent)
foliar necrosis to 2-year-old fourwing saltbush plants
(table 3). Evidence of initial phytotoxicity caused by sulfometuron at 0.05 kglha (25 percent necrosis) was not
present after 90 days. There was no apparent injury
to 2-year-old fourwing saltbush 90 days after sprays of
acifluorfen, fluazifop-P, clopyralid, or sulfometuron were
applied in June. Mature fourwing saltbush plants have
been reported to be tolerant to sprays of clopyralid applied
at rates of 0.56 to 1.12 kglha (Jacoby and others 1981).
Metsulfuron applied at 0.02 kglha in October caused
moderate to severe foliar necrosis (54 percent) of the
2-year-old plants (table 4). October applications of the
other herbicides caused little or no injury.
2
90
206
124
84
38
114
1Gb
42b
76ab
8b
2b
158a
Autumn planting
Trifluralin
0.8
Oryzalin
1.1
Ethalfluralin 1.9
Metolachlor 2.0
Alachlor
2.8
None
10
40
14
12
4
31
2
2
2
2
2
12
10
118
40
24
10
60
1
Means within a column and planting season followed by
similar lower case letters or without letters are not significantly
different (P = 0.05).
2
Average of two experiments.
307
Table 5-Canopy cover (percent) and standing crop (g/m2 )
of competing vegetation 90 days after spring or
autumn applications of postemergence herbicides
to fourwing saltbush plantings near San Angelo,
TX 1
Table 3-Necrosis (percent) of four age classes of fourwing saltbush plants 15 and 90 days after spring applications
of selected postemergence herbicides near San Angelo,
TX 1
Treatment
Herbicide
Rate 1 month
Plant age class
4 months 9 months
2 years
kglha - - - - - - - - - Percent necrosis - - - - - - - - - -
Treatment
Herbicide
Rate
Canopy
cover
Weed standing cro~
Broadleaf Grasses
kglha
Percent
- - - - - - glrrfl - - - - -
15 days after treatment
Acifluorfen
0.56
Metsulfuron
.04
Fluazifop-P
.21
Clopyralid
.2B
Sulfometuron .05
Hand weeded
None
23b
B7a
5b
27b
7Ba
7b
Ob
14b
B1a
29b
21b
91a
12b
19b
29cde
79a
13de
35bcd
59ab
Be
44bc
Spring planting
Be
43a
12bc
3c
25b
2c
1c
Acifluorfen
Metsulfuron
Fluazifop-P
Clopyralid
Sulfometuron
None
0.56
.04
.21
.28
.05
17b
100a
Ob
25b
100a
Ob
Ob
17b
100a
25b
29b
94a
10b
15b
Ob
27cd
100a
94a
Bd
44bc
7b
Ob
63b
1b
7d
Ob
Ob
41bc
Acifluorfen
Metsulfuron
Fluazifop-P
Clopyralid
Sulfometuron
None
Plant age class
4 months 9 months
2 years
kglha - - - - - - - - - - Percent necrosis - - - - - - - - - 15 days after treatment
43b
7Ba
2cd
13c
53b
15ab
22a
5b
13abc
25a
3c
6b
Od
15ab
5b
3cd
4b
Bbc
17ab
1c
1c
16a
12ab
Oc
1c
Bb
Oc
Oc
90 days after treatment
Acifluorfen
0.56
Metsulfuron
.02
Fluazifop-P
.21
Clopyralid
.2B
Sulfometur:on .02
Hand weeded
None
7d
100a
O.d
40c
B3b
Od
Od
3c
51 a
9bc
9bc
31ab
2c
9bc
10c
1Bc
262a
3c
63a
4c
15bc
24b
2c
7c
0.56
.02
.21
.28
.02
21
15
13
30
B
40
16
12
52
32
26
56
80
38
2
116
14
156
The dominant weeds during the June 1988 experiment
were prostrate euphorbia (Euphorbia prostrata), Dakota
verbena, spear globemallow, queensdelight (Stillingia
sylvatica), browntop panicum (Panicum fasciculatum),
stinkgrass (Eragrostis cilianensis), and kleingrass. Only
sulfometuron applied at 0.05 kg/ha in June reduced weed
canopies compared to those on untreated plots (table 5).
All herbicides except fluazifop-P reduced broadleafed
weed standing crop compared to untreated plots.
Fluazifop-P applied at 0.21 kg/ha significantly reduced
the standing crop of grasses compared to clopyralid or
sulfometuron.
Weeds present during the October experiment, although not abundant, were similar to the spring experiment with the addition of common purslane, Texas filaree
(Erodium texanum), western ragweed, and common oats.
Weed canopies and standing crop were low for most herbicide-treated plots, but the means were not significantly
different (table 5).
Table 4-Necrosis (percent) of four age classes of fourwing saltbush plants 15 and 90 days after autumn applications
of selected postemergence herbicides near San Angelo,
TX 1
Acifluorfen
0.56
Metsulfuron
.02
Fluazifop-P
.21
Clopyralid
.2B
Sulfometuron .02
Hand weeded
None
20Bab
48bc
56 be
6c
190a
142ab
48bc
1
Means within a column and planting date followed by similar
lower case letters or without letters are not significantly different
(P=0.05).
Means within a column and evaluation date followed by similar lower
case letters are not significantly different (P= 0.05).
1
Treatment
Herbicide
Rate 1 month
74bc
42bc
Autumn planting
90 days after treatment
Acifluorfen
0.56
Metsulfuron
.04
Fluazifop-P
.21
Clopyralid
.28
Sulfometuron .05
Hand weeded
None
29abc
22bc
34ab
40a
16c
39ab
6b
54 a
4b
DISCUSSION
22b
10b
3b
Herbicides have been an effective tool for vegetation
manipulation to improve rangelands for many years,
but to our knowledge there have been no previous
attempts to use herbicides to enhance establishment
of forage shrub plantings. Metolachlor and alachlor
4b
1
Means within a column and evaluation date followed by similar lower
case letters are not significantly different (P = 0.05).
308
applied at planting appeared promising as preemergence
treatments, but weed control was temporary because of
the short half-life of these herbicides. Applications of
clopyralid or acifluorfen after weed emergence satisfactorily controlled broadleafed weeds, and postemergence applications offluazifop-P controlled grasses with no or only
slight phytotoxicity to fourwing saltbush seedlings and
established plants.
Single-herbicide treatments are unlikely to provide
acceptable suppression of both grasses and broadleafed
weeds in shrub plantings. Additional research is needed
to evaluate herbicide combinations and sequential applications of different herbicides. The integrated use of cultivation and selective herbicides might have application
in some shrub establishment efforts.
Postemergence herbicide treatments appear more
practical than preemergence treatments because of the
uncertainty of precipitation (and hence the uncertainty
of weed problems) in most areas where fourwing saltbush
is utilized for range improvement. Herbicidal control of
undesirable plants may not be a viable practice where
fourwing saltbush is planted in mixtures with grasses,
desirable forbs, or other shrub species.
The high level of seedling mortality observed under
the ideal conditions of hand weeding and irrigation in
this study suggests that some seeding failures that have
been attributed to interference from associated vegetation
may have been a result of poor seed quality or low vigor
offourwing saltbush seedlings. Additional research on
increasing fourwing saltbush seed quality and seedling
vigor appears warranted.
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309