mass
May 1981

Response of
Camphorweed

and Associated

Vegetation
to Herbicides

and Prescribed
Burning  

The Texas Agricultural Experiment Station
Neville P. Clarke, Director, College Station, Texas
The Texas A&M University System

f" ‘ w;

Contents

SUMMARY
INTRODUCTION
MATERIALS AND METHODS
Study Area
Herbicide Treatments
Prescribed Burning
RESULTS AND DISCUSSION
Responses to Herbicides
PrescribedBurning
CONCLUSIONS
LITERATURE CITED
ACKNOWLEDGMENTS
METRIC —— ENGLISH EQUIVALENTS

®®®\I@U1U‘I-I>-h-J>QUQI\J

Summary

Camphorweed, an annual broadleaved plant, occurs primarily on sandy
sites in Texas, most commonly within 5O kilometers of the coast. During the
past ten years, however, camphorweed has spread 175 kilometers inland. The
recent spread of camphorweed and its persistence on rangeland are presently
of concern to South Texas livestock producers, but effective control methods
have not previously been developed.

Research was conducted in Jim Hogg County in the southern portion of
the South Texas Plains from May 1977 through August 1979. Camphorweed
was effectively controlled by a single application of 2,4-D ester or amine
formulations at 0.6 or 1 .1 kilograms per hectare (kg/ha) applied as a broadcast
spray from late winter to early summer. Broadcast applications of 0.6 or 1.1
kg/ha of dicamba+2,4-D (1:3), 2,4,5-T+picloram (1:1), or 0.14 kg/ha of
picloram alone were also effective for camphorweed control. The herbicide
sprays reduced the population densities of desirable broadleaves for the
growing season of treatment only. Pelleted picloram or tebuthiuron at 0.6 or
1.2 kg (active ingredient)/ha were equally as effective as herbicide sprays
applied at the same rates. A cool-season burn applied with a light, fine fuel
load; moderate wind speed; and low relative humidity significantly reduced
the density of live camphorweed, slightly decreased herbaceous standing crop,
and increased utilization of herbaceous standing crop during the first growing
season. A camphorweed management program might include initial use of
herbicides to reduce the camphorweed infestation, followed by periodic
burning to suppress reinvasion of this troublesome weed.

2

Response of Camphorweed and Associated Vegetation
t0 Herbicides and Prescribed Burning

l]. L. MUTZ, C. l. SCIFRES, AND C. W. HANSELKA*

Introduction

Camphorweed (Heterotheca subaxi/laris [Lam.]
Britt & Rusby) is an annual, aromatic, herbaceous mem-
ber of the Compositae. It typically develops slender,
procumbent to erect stems and occurs in coastal areas
from New Jersey to Tamaulipas, Mexico (Correll and
Johnston, 1970). Camphorweed occurs primarily on
sandy sites in Texas and is most common within 5O
kilometers (km) of the coast. However, land owners and
rangeland resource managers have observed that cam-
phorweed has increased its range westward during the
past 1O years, and well-developed stands now occur on
sandy range sites 175 km inland. As its range extended
westward, camphorweed was first observed in turnrows
of cultivated fields, but it is now a dominant invader of
many sandy range sites ranging from poor to good
condition. Once dense stands of camphorweed are es-
tablished on a range site, production of desirable vegeta-
tion diminishes. The recent spread of camphorweed and
its persistence on rangeland are presently of concern to
South Texas livestock producers.

Camphorweed produces yellow flowers from late
summer through early fall. No research has been con-
ducted in Texas on germination behavior of camphor-
wgeed seeds (achenes). However, camphorweed
achenes germinated in the spring and the fall in North
Carolina (Awang and Monaco, 1978) while germination
occurred only in the fall in Kentucky (Baskin and Baskin,
1976). Achenes of camphorweed exhibit germination
dimorphism (Awang and Monaco, 1978). Freshly-

 

*. pectively, assistant range scientist and professor, The Texas Ag-
. ultural Experiment Station (Texas A&M University Agricultural
/ earch and Extension Center at Corpus Christi and the Department
giange Science); and area range specialist, Texas Agricultural
ension Service, Corpus Christi.

KEYWQRDS: Camphorweed/range weed control/herbicides/pre-
scribed burning/applied ecology/range management.

matured disk achenes will germinate in light or darkness
over a wide range of temperatures immediately upon
dispersal. Ray achenes are dormant at dispersal and
must afterripen before they are capable of germination.
High temperatures promote afterripening while low tem-
peratures prolongdormancy. Since seed dispersal oc-
curs in the fall, germination of ray achenes is delayed for
at least a year after maturation of the parent plant'(Baskin
and Baskin, 1976). This mechanism ensures perpetua-
tion of infestations through periods when environmental
conditions are not favorable for seed germination and
seedling establishment.

Camphorweed seedlings emerge in the spring and
early fall on South Texas rangelands. Seedlings which
emerge in the fall overwinter as rosettes‘until spring
when active growth is resumed following rainfall. Based
on research with other range weeds such as common
broomweed (Xanthocepha/um dracuncu/oides), foliar-
applied herbicides are generally most effective when
applied during the seedling, rosette, or stem elongation
stages of growth, if environmental conditions are not
limiting to herbicide absorption and translocation (Sci-
fres, Hahn and Brock, 1971).

Results from commercial applications of conven-
tional herbicides such as 2,4-D ([2,4-dichlorophenoxy]
acetic acid) for control of camphorweed have resulted in
erratic control} Since camphorweed has only recently
been recognized as a management problem on Texas
rangeland, effective control methods have not been
developed. However, application of 4.5 kilograms per
hectare (kg/ha) of asulam (methyl sulfanilylcarbamate) in
July controlled camphorweed in North Carolina
(Skroach, 1975). Awang and Monaco (1978) reported
that camphorweed can be controlled with a number of
herbicides commonly used in agronomic crops.

‘Carlyn Hoffman, Texas Agricultural Extension Service, 1976, person-
al communication.

 ‘ w;

Applications of these herbicides in the winter when
the camphorweed plants were in the rosette stage were
not as effective as applications in the spring after the
camphorweed had developed stems. Translocated her-
bicides were more effective than contact herbicides
when treating camphorweed in later stages of develop-
ment. None of the herbicides that are effective for
controlling camphorweed in agronomic crops are regis-
tered by the Environmental Protection Agency for range
weed control in Texas. Destruction of the aerial parts of
camphorweed plants developed beyond the rosette
stage is not necessarily effective for control since the
plants may resprout from any live tissues remaining near
the ground.

The objectives of this research were to evaluate (1)
various herbicides, herbicide combinations, and formu-
lations for camphorweed control; (2) the potential of
cool-season burns for suppressing camphorweed; and
(3) the response of associated herbaceous vegetation to
camphorweed control.

Materials and Methods
Study Area

Research was conducted on a Nueces-Sarita soil
association in Jim Hogg County approximately 3O km
south of Hebbronville, Texas, in the southern portion of
the South Texas Plains. Typically, the Nueces-Sarita
association consists of Nueces series, 45 percent; Sarita
series, 33 percent; and Delmita and Falfurrias series and
active sand dunes, 22 percent. Formed from wind-
deposited materials, these soils are deep, nearly level to
gently sloping, and gently undulating. They are moder-
ately well drained and have a low water-holding
capacky.

Average annual precipitation varies from about 4O
to 9O centimeters (cm) with rainfall peaks occurring from
May to lune and in September (Waldrip, 1957). Sum-
mers are typically dry with high temperatures and high
evaporation rates. Most of the South Texas Plains is used
for range livestock production but a considerable
amount of row-crop production occurs in the immediate
study area.

Potential vegetation for the study site includes sea-
coast bluestem (5chizachyrium scoparium var. lit-
toralis), several bristlegrasses (Setaria spp.), Paspalum
spp., Chloris spp., and Trichloris spp., longspike silver
bluestem (Bothrioch/oa saccharoides var. lon-
gipaniculata), big sandbur (Cenchrus myosuroides), and
tanglehead (Heteropogon contortus). Continuous year-
long grazing has resulted in a botanical composition
consisting mostly of species of relatively low quality for
grazing such‘ as threeawns (Aristida spp.), Pan American
balsamscale (E/yonurus tripsacoides), and low-growing
panicums (Dichanthelium spp.). Many herbaceous
broadleaved species, several of which are important
diets of wildlife and domestic livestock, are also found
on the sandy sites. Large tree-type honey mesquites
(Prosopis glandulosa Torr. var. glandulosa), 5 to 7 me-
ters (m) tall, are scattered throughout this plant commu-

4

nity. These honey mesquite mottes provide shade and
cover for domestic livestock and game animals.

._\\

Herbicide Treatments 

Herbicide sprays were applied with a tractor-
mounted boom sprayer on May 3, 1977; February 23,
1978; and June 13, 1979 to duplicate 0.2-ha plots. All
experiments were designed as randomized complete
blocks. Herbicide treatments included the butoxy-
ethanol ester of 2,4-D at 0.6 and 1.1 kg/ha, dimethyl-
amine salt of 2,4-D at 0.6 and 1.1 kg/ha, 2,4,5-T
([2,4,5-trichlorophenoxy] acetic acid) plus picloram (4-
amino-3,5,6-trichloropicolinic acid) (1 :1) at 0.3 and 0.6
kg/ha of total herbicide; dicamba (3,6-dichloro-o-anisic-
acid) plus 2,4-D (1:3) at 0.6 and 1.1 kg/ha of total
herbicide; and picloram as the potassium salt at 0. 4
kg/ha. Liquid herbicides were applied in 187 liters per
hectare (l/ha) of water. Picloram pellets (5 or 10 percent
active ingredient) and tebuthiuron (N-[5-(1,1-
dimethylethyl)-1,3,4-thiadiazol-2-y1]-N,N’-dimethyl-
urea) pellets (20 percent active ingredient) were applied
at 0.6 or 1.1 kg/ha (active ingredient) in the experiment
begun on May 3, 1977. The herbicide pellets were
applied with a tractor-mounted broadcast spreader nor-
mally used for applying seed or dry fertilizers. At least
ten soil samples were randomly collected to a depth of
15 cm for gravimetric determination of soil-water con-
tent on each date of herbicide application.

The number of camphorweeds and other broadleaf
herbaceous plants was counted prior to treatment and at
selected times post-treatment within 10 permanently
located, 0.25-m2 areas equidistantly spaced along a
diagonal line across each plot. Plots treated on May 3,
1977 were evaluated on May 1, 1977 (pretreatment
counts); August 4, 1977; December 14, 1977; June 12,
1978; and August 2, 1979. Plots sprayed on February
23, 1978 were evaluated on February 23, 1978 (pre-
treatment counts); December 12, 1978; and June 12,
1978. Plots sprayed on June 13, 1978 were evaluated
pretreatment on June 23, 1978 and on September 11,
1978. Percentage reduction in live camphorweed plants
was based on pretreatment counts. All data were statisti-
cally analyzed using analysis of variance (Ostle, 1963).
Mean difference was compared with Duncan's multiple
range test at the 0.05 level. "

Prescribed Burning

On February 23, 1978, a 12-ha sandy site support-
ing an average of 2,270 camphorweed plants/ha was
burned with a headfire. Prior to burning, ten permanent
belt transects, about 36 m long by 2.7 m wide, were
established within the area to be burned and ten similar
transects were established in an adjacent untreated area.
Camphorweed densities on each area were estimated by
counting the number of plants within the belt transects.
Immediately prior to burning, standing fine fuel (starti-
ing crop plus mulch) in ten, 0.25-m sampling area's,
equidistantly spaced along the permanent lines, k/
harvested to ground level and the mulch collectcs.
Because of freezing weather prior to sampling, all stand-
ing fine fuel was dead. All fuel samples were sealed in

metal cans, air-dried for 48 hours at 65° C, and
weighed. Oven-dry water content of soil was

   termined on ten samples recovered from 0 to 8-, 8 to
*1 .1, and 15 to 30 cm deep from the burned plot.

Environmental conditions monitored were relative
humidity determined with a sling psychrometer; air
temperature at 2 m; soil temperature at 2 cm; and wind
velocity and direction at a height of 2 m with a hand-
held anemometer.

Asbestos cards supporting temperature-sensitive
pellets (ranging in sensitivity from 37° to 650° C in 37° C
increments) were used at 1O randomly located monitor-
ing stations to estimate maximum temperature during
the burn at 3 cm above ground level.

A backfire was ignited on the leeward side and

fillowed to burn approximately 15 to 2O m into the area
Jefore the headfire was ignited (Scifres, 1980). Flame
front speed (meters per minute) was determined by
placing marked metal stakes 22 m apart at two stations.
The time required for the flame front to travel between
the stakes at each station was recorded and averaged.
Flame height (m) was estimated visually.

Ten portable grazing exclosures were established
after burning on the burned area and adjacent unburned
area to facilitate evaluation of range forage production
and utilization. The exclosures were constructed from
10-gauge welded concrete reinforcement wire with 15
by 15-cm openings. Each exclosure was approximately
3 m tall and 3.5 m in diameter.

The term ”forage utilization" will be used here to
mean grass forage loss-the combination of losses such
as weathering, trampling, and consumption bylwild
animals and insects as well as forage consumed by
livestock. The exclosures were placed at the mid-point
of each belt transect. On August 10, 1978, herbaceous
vegetation in O.25-m2 sampling areas was harvested to a
2.5-cm stubble height within each exclosure and from a
randomly-selected grazed area approximately 2 m from
the exclosure. The herbage in each sampling area was
divided into grasses and broadleaves, air dried, and
weighed. Differences in herbaceous standing crop be-
tween caged and grazed samples were used to estimate
forage utilization for that period. After harvesting, the
exclosures were moved to a randomly determined point
along the permanent line and secured until the second
harvest on August 2, 1979.

Results and Discussion

i Responses to Herbicides

Environmental conditions during herbicide ap-
plication. On May 3, 1977, near optimum environmen-
tal conditions prevailed for control of annual broadleaf
plants with foliar-applied, translocated herbicides. Air
pmperature was 25° to 27°C, relative humidity was no
less than 6O percent, and wind speed was O to 12 km/hr

léring the application of sprays. Soil-water content in

e surface 15 cm averaged 9 percent, near field capaci-
ty (10 percent) for the sandy soil of the study area.
Camphorweed plants ranged from 2.5 to 15 cm tall, but

approximately 75 percent of the population was less
than 7 cm tall.

Environmental conditions for control of camphor-
weed with foliar sprays were not considered favorable
on February 23, 1978. Soil-water content averaged 4
percent on an oven-dry basis—near wilting point for the
soil of the study area. Air temperatures were 16° to 22°C,
and relative humidity was less than 5O percent. Wind
speed was less than 8 km/hr during herbicide applica-
tion. The camphorweed plants were 2.5 to 7 cm tall,
and showed signs of foliar necrosis, apparently the result
of freezing weather and dry conditions prior to treat-
ment.

The study site received less than normal rainfall
throughout the winter and spring of 1979. However, by
late May 1979, precipitation provided enough moisture
for the camphorweed to germinate and initiate growth.
When the experiment was installed on June 13, 1979,
soil-water content was about 5 percent, air temperature
was 33°C, and relative humidity was 85 percent or
higher during herbicide application. The camphorweeds
were 1O to 15 cm tall and actively growing. These
conditions were considered near optimum for herbicide
control of the camphorweed based on results with other
herbaceous weeds (Scifres, Hahn, and Brock, 1971).

Camphorweed control. Since there were no sig-
nificant differences in the response of camphorweed to
herbicides between the May 3, 1977 and June 13, 1979
application dates, data were pooled within evaluation
times where possible. All herbicide sprays resulted in
excellent camphorweed control for 13 months (Table 1).
Treated areas were virtually free of camphorweed for
two growing seasons. Thus, O.6 to 1.1 kg/ha of her-
bicides normally used for herbaceous weed control,
2,4-D (ester or amine formulation) or dicamba plus 2,4-
D (3:1), applied in the spring or early summer, will
effectively control camphorweed if growing conditions
are favorable for herbicidal activity. If associated species
such as honey mesquite are also to be controlled, appli-
cation of 2,4,5-T + picloram (1:1) at O.6 or 1.1 kg/ha
may be justified.

Desirable broadleaf plants, especially legumes such
as Texas snoutbean (Rhyncosia americana), least snout-
bean (Rhyncosia minima), and coast indigo (Indigo
miniata var. miniata) were eliminated from the botanical
composition for 6 to 7 months following application of
the herbicide sprays. However, the desirable plants
generally had increased in density by 13 months follow-
ing application of several of the herbicides, compared to
untreated plots (Table 2). The greatest increase in desir-
able plant density occurred on plots treated with the
lower rate of 2,4-D ester, picloram, and either rate of
2,4,5-T plus picloram or dicamba plus 2,4-D. Although
there was a general trend for camphorweed densities to
be lower on treated than on untreated plots at 27 months
(third growing season) following application of the her-
bicide sprays, reinfestation was extensive except on
plots receiving the high application rate of 2,4,5-T plus
picloram (Table 1). ' t

Reduction of live camphorweed plants exceeded
9O percent within 3 months after application of pelleted

5

1S. . v
"i!

herbicides on May 3, 1977 except where the 1O percent
picloram pellets were applied at 0.6 kg/ha active ingre-
dient. The 10 percent picloram pellets applied at 0.6
kg/ha controlled 75 percent of the camphorweeds with-
in 9O days after application (Table 1). Camphorweed

density was reduced by 95 and 98 percent at 9O days

after application of the 5 percent picloram pellets at 0.6
and 1.1 kg/ha, respectively. The lower initial control
from the 10 percent picloram compared to the 5 percent
formulation at 0.6 kg/ha was attributed to more even
distribution of the 5percent formulation. At 13 months
following application, there was no significant differ-
ence in control of camphorweed between the two for-
mulations of picloram pellets, regardless of application

rate. Tebuthiuron at 0.6 and 1.2 kg/ha controlled 9O and g

97 percent of the camphorweed, respectively, after 12
months.

Although there was a considerable amount of varia-
tion in density of desirable plants among plots receiving
the pelleted herbicide treatments, the general trend indi-
cated no change in density compared to that of the
untreated plots, with the exception of reduced density of
forbs on plots treated with tebuthiuron at 1.1 kg/ha
(Table 2). Herbicidal damage to all herbaceous plants
was apparent for at least 13 months on plots treated with
1.1 kg/ha of tebuthiuron. The desirable forb population
was decreased to 4.5 plants/m“, compared to 15.4
plants/m“ on untreated areas. The pelleted herbicides
were no more effective than the herbicide sprays for

Table 1. Average reduction (%) in density of live camphorweed plants
after application of various herbicides, rates, and formulations with
ground equipment on May 3, 1977 and June 13, 1979 near Hebbron-
ville, Texas

Treatment
Months after application“
Rate
Herbicide(s) (kg/ha) 3 7 13 27b
None 0 O a 0 ‘a 0 a 0 a
Sprays

2,4-D (ester) 0.6 97 C 100 C 99 C 2O bc
2,4-D (ester) 1.1 98 c 99 c 100 C 4O cd
2,4-D (amine) 0.6 100 C 99 C 89 b 0 a
2,4-D (amine) 1.1 1OO C 1OO C 96 C 2O bC
2,4,5-T+picloram (1: ) 0.3 99 c 99 c 99 C 15 ab‘

1

2,4,5-T+picloram (1:1) 0.6 1OO C 1OO C 99 C 6O d
)
)

Dicamba+2,4-D (1 :3 0.6 99 C 100 C 99 C 3O C
Dicamba+2,4-D (1 :3 1.1 99 C 100 C 99 C 3O C
Picloram 0.14 9O C 95 C 96 C 5 a
Pellets
Picloram (5%) 0.6 95 C 97 C 98 C 3O C
Picloram (5%) -:=__ A 1.2 98 C 98 C 98 C 10 ab
Picloram (10%)'* 0.6 75 b 87 b 98 C 2O bc
Picloram (10%) 1.2 99 C 99 C 99 C 2O bc
Tebuthiuron (20%) 0.6 9O C 97 c 98 C 15 ab
Tebuthiuron (20%) 1.2 97 C 95 C 99 C 0 a

“Means within a column followed by the same letter are not significantly
different at the 5 percent level according to Duncan's multiple range- test.

bData based on May 3, 1977 applications only.

Table 2. Density (plants/m“) of desirable broadleaved plants at 13

months followinng application of various herbicides, formulatidfifi

and rates on May 3, 1977 near Hebbronville, Texas

Treatment
Rate Plant
Herbicide(s) (kg/ha) density“
None -- 15.4 C
Sprays
2,4-D (ester) 0.6 31.3 f
2,4-D (ester) 1.1 18.7 cd
2,4-D (amine) 0.6 17.2 cd
2,4-D (amine) . 1.1 15.9 cd
2,4,5-T+picloram (1:1) 0.3 31.3 f
2,4,5-T+picloram (1:1) 0.6 25.6 e
Dicamba+2,4-D (113) 0.6 33.1 fQ)
Dicamba+2,4-D (1:3) 1.1 31.8 f
Picloram 0.14 29.9 ef
Pellets
Picloram (5%) g 0.6 11.3 b
Picloram (5%) 1.2 11.4 b
Picloram (10%) 0.6 11.5 b
Picloram (10%) 1.2 22.1 de
Tebuthiuron (20%) 0.6 13.2 bc
Tebuthiuron (20%) 1.2 4.5 a

“Means followed by the same letter are not significantly different at the 5 percent
level according to Duncan's multiple range test.

controlling camphorweed into the third growing season
after application (Table 1).

Although spraying conditions were not considered
optimum during the February 23, 1978 application,
excellent camphorweed control occurred for at least 6
months following application of the 2,4-D ester or
amine at 0.6 or 1.1 kg/ha and of dicamba plus 2,4-D at
0.6 kg/ha (Table 3). Because of cold weather, desirable
broadleaf plants were not present during the herbicide
application and, consequently, were not affected by the
treatments. Within 6 months following treatment,
broadleaf plant densities ranged from about 12 to 19
plants/m“, regardless of herbicide(s) or rate applied
(Table 3).

Prescribed Burning

Burning Conditions. The total fine fuel was 2,340
kg/ha of which 1,204 kg/ha was standing material. The
standing dead fine fuel contained about 12 percent
water while the mulch contained nearly 1O percent at
the time of burning. Soil-water content was about 4
percent. The burned area supported approximately
2,270 camphorweed plants/ha prior to treatment while
the adjacent unburned area supported about 1,030
plants/ha. Air temperature was 19°C, and relative
humidity was 25 percent during the burn. Wind speeds
ranged from 12to 24 km/hr, causing the flame front
move at approximately 31 m/minute and to attain

heights of 4.5 to 6 m. Maximum fire temperature’"\\_

ground level was 205°C, with a temperature of 156
occurring at most recording stations.

Table 3. Reduction (%) in number of live camphorweed plants and

psity (plants/mz) at 6 months following application of 2,4-D and

, .amba+2,4-D with ground equipment on February 23, 1978 to a
sandy site near Hebbronville, Texas

Treatment
Camphorweed

- Rate reduction Forb

Herbicide (kg/ha) (%)“‘ densitya
None -- 0 13.6
2,4-D ester 0.6 99 18.9
2,4-D ester 1.1 100 14.7
2,4-D amine 0.6 100 12.2
2,4-D amine 1.1 100 16.0
Dicamba+ 2,4-o 0.6 100 14.9

“No significant difference among means (P<.05).

Responses to burning. At 6 months after installa-
tion of the fire (August 10, 1978), the burned area was
virtually free of camphorweed. The adjacent, unburned
area supported approximately 495 plants/ha. Natural
mortality of camphorweed was high during the summer,
but this is common among annual plants and probably
accounts for the apparent ”residual control” noted the
third growing season after application of some her-
bicides.

After burning, the study area did not receive signifi-
cant rainfall until the latter part of May. Consequently,
forage response was minimal during that period, and
herbage production and utilization were not measur-
able. On August 10, 1978, standing crop produced
since date of burn (February 23, 1978) was 2,359 kg/ha
on the burned area and 2,572 kg/ha on the adjacent
unburned area. Grass accounted for 2,080 kg/ha of the
standing crop, and broadleaf plants produced 278 kg/ha
on the burned area (Table 4). Grass standing crop on the
unburned areas was 2,079 kg/ha.

At 6 months following burning, utilization of the
standing crop on the burned area was greater than on
the unburned area (Table 4). More than 90 percent of
the total herbaceous standing crop was utilized on the
burned area while 74 percent was utilized on the un-
burned area. On the burned area, about 95 percent of
the grass standing crop was utilized, while only 52
percent of the broadleaves was utilized. On the un-
burned site, about 60 percent of the broadleaves was

jJIlllZGd, and 96 percent of the grass standing crop.
" On August 2, 1979, 18 months following burning,
the total standing crop in the exclosures protected from
grazing was 2,576 kg/ha, while on the unburned area
the standing crop was 2,632 kg/ha. Forage utilization 18
months after burning was relatively low, reflecting a
reduction in stocking rate on the study area, and was
fly slightly higher on the burned site than on the
nburned site (Table 4). Although camphorweed was
'dent in the burned plot at 18 months following
oatment, the density was estimated at 40 percent less
than on the unburned plot.

Conclusions

These data indicate that camphorweed can be ef-
fectively controlled with applications of 2,4-D ester or
amine at 0.6 or 1.1 kg/ha from late winter to early
summer. Unless other difficult-to-control herbaceous
weeds are present in the stand, the higher rates of 2,4-D
or inclusion of herbicides such as dicamba or picloram
would probably not be warranted. However, where
control of woody species such as honey mesquite is also
desired, dicamba or mixtures of 2,4,5-T and picloram
may be the most effective of the herbicides evaluated in
this study. i _ a

Applications of picloram pellets (5 or 10 percent
active ingredient) or tebuthiuron pellets (20 percent
active ingredient) in the spring were equally effective for
camphorweed control as equivalent rates of the her-
bicide sprays evaluated. However, the pellet formula-
tions offer an alternative to sprays where spray drift
poses a potential hazard to adjacent herbicide-
susceptible crops. All herbicide treatments reduced the
density of desirable forbs, primarily legumes, for at least
one growing season after spring application, but broad-
leaf plants other than camphorweed were not affected
by winter application of herbicide sprays.

A cool-season prescribed burn conducted with a
relatively low standing fine fuel load and moderate wind
speeds but with a low relative humidity effectively re-
duced the camphorweed population for one growing
season. Based on these results, range livestock produc-
ers desiring to develop management systems for range-
land supporting heavy infestations of camphorweed
might consider selecting an appropriate herbicide as an
initial treatment to be applied in winter or spring. Fol-
lowing the herbicide application, periodic cool-season
burns may effectively suppress invading camphorweeds.

Table 4. Total standing crop (kg/ha) and percentage utilized from
February 23, 1978 to August 10, 1978 and from August 10, 1978 to
August 2, 1979, and numbers of live camphorweeds per hectare on
August 10, 1978 and August 2, 1979, on burned and unburned sites
near Hebbronville, Texas \

Total standing crop

Produced Utilized Camphorweed
(kg/ha) (%) plants/baa

Grazing
Treatment period

February 23, 1978
to 2359 92 0
August 10, 1978 a
August 10, 1978
to 2576
August 2, 1979

Unburned February 23, 1978

to 2572 74 495
August 10, 1978
August 10, 1978

to 2632 21
August 2, 1979

Burned

33 6768

11,444

“Camphorweed densities recorded on last day_of grazing period.

T‘ ‘ w;

Literature Cited

Awang, M. B. and T. J. Monaco. 1978. Germination,
growth, development, and control of camphor-
weed (Heterotheca subaxi//aris). Weed Sci. 26:
51-57.

a Baskin, W., and C. C. Baskin. 1976. Germination di-

morphism in Heterotheca subaxi/laris var. subaxil-
Iaris. Bull. Torrey Bot. Club. 103:201-206.

Correll, D. S. and M. C. Johnston. 1970. Manual of the
vascular plants of Texas. Texas Research Found.
Renner, Texas. 1881 pp.

Ostle, B. 1963. Statistics in research. Iowa State Univ.
Press. Ames, Iowa. 585 pp.

Acknowledgments

Land and partial financial support for this research
furnished by the Eshleman-Vogt Ranch near Hebbron-
ville, Texas, is greatly appreciated. The authors are
grateful to T. C. Longnecker for his help in initiating the
research project, Julia Scifres for typing and preparing
the manuscript, and W. C. Mohr and Eldon Yeager for
their efforts in plot establishment, maintenance, and
evaluation. Also, the interest of Harold, Harris, and
Charles Kaffie in this project is greatly appreciated.

Scifres, C. J. 1980. Brush Management. Principles 
practices for Texas and the Southwest. Texas AL i
Univ. Press. 360 pp.

Scifres, C. J., R. R. Hahn, and J. H. Brock. 1971.
Phenology and control of common broomweed on
Texas rangelands. J. Range Manage. 24:370-373.

Skroach, W. A. 1975. Weeds in horticultural apples.
South. Weed Sci. Soc. Res. Rep. 28:157.

Waldrip, W. J. 1957. Farming and ranching risk as
influenced by rainfall. Ill. TAES Bull. MP-241.
20 pp. t .

"3

YD
‘Q.

Metricwg- English Equivalents

Metric English

unit equivalent
Centimeter (cm) 0.4 inch
Gram (g) 0.035 ounce" (weight)
Hectare (ha) 2.47 acres
Kilogram per hectare (kg/ha) 0.89 pound per acre
Kilometer (km) 0.62 statute mile
Liter (l) 0.26 gallon
Meter (m) 3.28 feet

Degrees centigrade (°c) >< 1.8 + 32 Degrees farenheit

Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of
the product by The Texas Agricultural Experiment Station and does not imply its approval to the

exclusion of other products that also may be suitable.

All programs and information of The Texas Agricultural Experiment Station are available to

) 

everyone without regard to race, ethnic origin, religion, sex, and age. t, 

The Texas Agricultural Experiment Station, Neville P. Clarke, Director, College Station, Texas

2M — 5-81