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B-1728

Texas Agricultural Experiment Station 

The Texas A&M University System

 

Herbicide Absorption and
Transport in
Honey Mesquite

and Associated Woody Plants in Texas

    
    

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Contents

Introduction ................................................................................................................................ .. 1
Historical Review ........................................................................................................................ ..1 w
Improved Quantification of Herbicides ........................................................................................ ..2
Foliar Absorption ........................................................................................................................ ..3
Herbicide Type .................................................................................................................... ..3
Herbicide Formulation .......................................................................................................... ..4
Herbicide Mixtures .............................................................................................................. ..4
Carriers and Adjuvants ........................................................................................................ ..5
Spray Characteristics ............................................................................................................ ..6
pH Affects ..................................................................................  ........................................ ..6
Air Temperature and Relative Humidity .............................................................................. ..7
Rainfall ................................................................................................................................ ..7
Time of Day ........................................................................................................................ ..7
Moisture Stress .................................................................................................................... ..8
Light .................................................................................................................................... ..8
Leaf Structure and Development .......................................................................................... ..8
Metabolism, Degradation and Mode of Action ....................................................... ..~ ............. ..9
Translocation .............................................................................................................................. . . 1O
Herbicide Type .................................................................................................................. ..11
Herbicide Formulation ........................................................................................................ ..12
Herbicide Mixtures ............................................................................................................ ..13
Carriers and Adjuvants ...................................................................................................... ..14
Spray Characteristics .......................................................................................................... ..14
pH Affects .......................................................................................................................... ..15
Temperature and Relative Humidity .................................................................................. ..15
Rainfall .............................................................................................................................. ..15
Time of Day ...................................................................................................................... ..15
Light .................................................................................................................................. ..15
Moisture Stress .................................................................................................................. ..15
Other Factors ...................................................................................................................... ..16
Root Penetration and Translocation ..................................  ........................................................ ..16
Laboratory and Greenhouse Studies .................................................................................... ..17
Field Studies ...................................................................................................................... ..17
Summary .................................................................................................................................. ..17
Herbicides Discussed ................................................................................................................ ..18
Literature Cited .......................................................................................................................... ..19

"5

Herbicide Absorption and Transport
in Honey Mesquite and Associated
Woody Plants in Texas

Rodney W. Bovey*

Introduction

According to information published in the
1960s (99), honey mesquite grows on more
than half (about 22.7 million hectares) of Texas
rangeland. Surveys in the mid-1980s indicated
that acreages infested had changed little at
about 5O percent of all rangeland in Texas (2).
Several reasons are evident for this unchanged
acreage including the small acreage treated
each year with herbicides (< 0.5 million
hectares) (103), the sometimes lack of effective
treatment (32), and the rapid reinfestation of
new areas (43). In addition, attitudes toward
brush management have changed over the last
several years and more brush is tolerated in
ranch planning and retained for wildlife habi-
tat.

Despite new attitudes and government regu-
lations, herbicides will continue to be essential
tools alone and with other management prac-
tices (mechanical, fire, biological) for weed and
brush management on pastures and rangeland.

This review summarizes the work done on
absorption and translocation of herbicides in
honey mesquite and associated woody and
herbaceous plants in Texas. Factors affecting
herbicide success and environmental response
are reviewed so that this reference can be used
as a basis for future research and direction.

Historical Review

As early as 1948, Fisher and Young (54)
reported that sodium arsenite, sodium arsenate,
sodium chlorate, ammonium sulfamate, sulfam-
ic acid, ammonium thiocyanate, 2,4-D, and
2,4,5-T were the only chemicals out of several
hundred tested that were absorbed by the

*Adjunct Professor, Department of Rangeland Ecology and

Management, Texas A&M University, College Station, TX
77843. Former Research Agronomist, U.S. Department of
Agriculture, Agricultural Research Service, College Station,
TX.

foliage and translocated in sufficient amounts
to kill dormant buds on the) underground stems
of honey mesquite. However, the researchers
indicated that ideal conditions of absorption
and translocation of chemicals were seldom
attained in the Southwest, since moist contact
of the chemical with the leaf surface was
required for long periods (8 hours). Increasing
chemical concentration on leaf surfaces above
lethal concentrations did not improve translo-
cation.

It was reported in 1949 that an ester of
2,4,5-T applied to the foliage of mesquite was a
more effective treatment than several formula-
tions of 2,4-D or other chemicals (108). During
the same year, aerial applications were made to
mesquite in different seasons (55). Most effec-
tive control was obtained at the full leaf stage
(spring) with ample soil moisture (90 percent
canopy reduction and 25 percent mortality). By
1951, an estimated 0.2 million hectares of
honey mesquite in Texas were treated commer-
cially with broadcast foliar sprays of the ester
of 2,4,5-T (61).

In 1956, Fisher et al. (57) defined the follow-
ing factors responsible for the effective control
of mesquite with Z,4,5-T.

1. Effective control depends upon transloca-
tion of a toxic amount of Z,4,5-T from
foliage to the crown tissues.

2. Greatest translocation of 2,4,5-T occurs
during a 50- to 90-day period after the
first leaves emerge in the spring (most
favorable time of treatment).

3. Maximum translocation of 2,4,5-T occurs
when total sugar content in roots is accu-
mulating at a rapid rate following the low
level at the beginning of the full leaf
stage.

4. Minimum translocation of 2,4,5-T occurs
when total sugars in roots are decreasing

rapidly and when reducing sugars are rel-
atively abundant.

5. Most effective control of mesquite with
2,4,5-T occurs when soil moisture is ade-
quate, a heavy foliage cover is present,
and after rapid growth of new leaves and
stems has ceased.

6. Effectiveness of aerial application of 2,4,5-
T is reduced when either drought-restrict-
ed growth or when intermittent rainfall
causes irregular foliage growth.

7. The herbicide 2,4,5-T is more effective
when applied to mesquite growing on
sandy loam and deep sandy soils com-
pared with heavy clay soils, and on small
plants with stems less than 8 cm in diam-
eter compared with larger trees.

8. Carriers, whether oils alone, oil-water
emulsions, or water alone, have no appar-
ent influence on the effectiveness of 2,4,5-
T applications when used at 37, 75, or
135 l ha'1 (liter per hectare) total volume.

9. A rate of 0.56 kg ha"1 (kg per hectare) of
low volatile ester of 2,4,5,-T in a 1 to 3
ratio of oil-water emulsion effectively and
economically controls mesquite.
Increasing the amount of 2,4,5-T does not

increase the percentage of mesquite
killed.

10. Droplet size of sprays, formulation of
2,4,5-T, and weather factors do not
appreciably affect the effectiveness of
2,4,5-T. However, these factors must be
considered in ease and safe handling of
the herbicide under field conditions.

Fisher et al. (53) defined the anatomy and
morphology of honey mesquite and showed
that the dormant buds on the underground
stem of mesquite must be destroyed in order to
kill the plant. Effective evaluation of absorp-
tion and translocation of the herbicide was
measured by plant response in discoloration or
killing of leaves, defoliation of leaves, and final-
ly death of the plant. Hull (62) did similar stud-
ies on seedling velvet mesquite in Arizona.

Young and Fisher (107) devised a rapid
method of testing the absorption and transloca-
tion of herbicides by spraying an exposed
branch and observing the effect on the leaves
of the sprayed branch compared with the
leaves on a shielded or protected branch.

Fisher and Young (56) also used a tip immer-
sion method to test translocation by immersing
the tip of a branch into a herbicide container
for a period of 1 to 24 hours and observing
translocation by plant effect. These methods
were very useful in determining the best herbi-
cides, formulation, chemistry, diluents, timing
of application, and environmental conditions
necessary for best results; although, they did
not quantify herbicide absorption and translo-
cation in plant tissue.

From these early studies, the most successful H

and economical broadcast herbicide treatment
for honey mesquite was aerial application of a
low volatile ester of 2,4,5-T (58). The herbicide
was applied in a 1 to 3 diesel oil/water emul-
sion carrier at 37 l ha'1 5O to 9O days after bud
break in the spring (59). Herbicide rates tested
were 0.56 to 1.1 kg ha-l (60).

Although the principles as outlined were
established more than 40 years ago, they are
still valid today for honey mesquite control
with hormone-type herbicides even though
2,4,5-T is no longer available. Fisher et al. (57)
indicated that the low volatile ester and sus-
pended acids of 2,4,5-T were more consistent
in killing mesquite than either the high volatile
esters or the amine formulations. Tschirley and
Hull (101), Reynolds and Tschirley (91), and
Valentine and Norris (102) also found that the
esters of 2,4,5-T were consistently more effec-
tive on velvet mesquite.

Improved Quantification
of Herbicides

The pioneering work of Crafts and co-work-
ers (44, 45, 46, 47) improved our understanding
of how assimilates move in the conducting tis-
sue of plants and introduced us to the use of
radio-labled herbicides to monitor their uptake
and movement in plants. Autoradiography
methods (47 ) indicated degree of absorption,
transport, and distribution in the plant, but
methods were not very quantitative. Merkle
and Davis (79, 80) were first to show that piclo-
ram and 2,4,5-T could quantitatively be deter-
mined in herbaceous plant tissue (Phaseolus vul-
garis L. var. Black Valentine bean) by use of gas
chromatography (GC). Morton et al. (89) com-
pared uptake and transport of carboxyl-labeled
and unlabeled butoxyethyl ester and ammoni-
um salt of 2,4,5-T by 3-year-old, field-grown
honey mesquite by liquid scintillation counting

and gas chromatography. Absorption of 2,4,5-T
was determined by assaying leaf-rinsing solu-
tions and extracts of treated leaves. Transport
of 2,4,5-T was measured by determining
amounts found in stem tissue. The methods of
analysis gave comparable results when extrac-
tion, cleanup, and analytical procedures were
identical.

Bovey et al. (20) showed that bioassays using
Puerto Rico 39 cucumber plants (Cucumis
sativus L.) and gas chromatography to detect
picloram in tropical soils gave comparable
results. Sunflower (Helianthus annuus L.), soy-
beans (Glycine max L.), cucumber, and field
bean were used as bioassays compared to GC
analysis to quantify nanogram quantities of
picloram in river sand and a sandy clay loam.
Results from GC analysis and bioassay meth-
ods were closely correlated, but GC demon-
strated less inherent variability than bioassay
methods (93).

There were no differences in spray deposit
on mesquite leaves whether determined fluoro-
metrically from a fluorescent dye in the spray
solution or determined chemically by gas chro-
matographic analysis. GC methods compared
favorably in all these experiments to other
means of herbicide analysis. Data in this report
are for herbicides detected from plant tissue
mainly by GC methods.

Foliar Absorption

Lethal amounts of foliar applied herbicides
must be absorbed by leaf and stem tissue and
translocated to the crown zone of honey mes-
quite and roots of other woody plant to effec-
tively control growth and/or cause mortality.
The following factors affect foliar absorption.

Herbicide type

Herbicides vary in rate and extent of foliar
penetration. Young and Fisher (54, 56, 107 ,,
109) found that 2,4,5-T was more readily
absorbed than many other chemicals tested,
including 2,4-D, by leaves of honey mesquite.
This was determined by plant response to the
herbicides (54, 56, 107, 109) and no actual
chemical content determinations were made.
Davis et al. (49) studied the uptake of picloram
and 2,4,5-T in leaves of 1O woody species,
including honey mesquite, and found that in
most species picloram entered faster and accu-

mulated at higher concentrations than 2,4,5-T,
14 and 48 hours after application. In other
studies (48), honey mesquite leaves also
absorbed picloram more rapidly and extensive-
ly than 2,4,5-T, but moisture stress reduced
foliar uptake of picloram, whereas absorption
of 2,4,5-T was unaffected. In winged elm
(Ulmus alata Michx.), moisture stress did not
affect absorption of picloram or 2,4,5-T. Bovey
and Mayeux (28) found higher concentrations
of clopyralid than 2,4,5-T, triclopyr, or picloram
in honey mesquite stems and roots 3, 10, and
3O days after application to soil or foliage in
the greenhouse.

More clopyralid than 2, 4, 5-T, triclopyr, or
picloram was usually detected in upper and
basal stem phloem and xylem in field-grown
honey mesquite (31, 87). Gas chromatographic
analysis of field-grown honey mesquite indicat-
ed that more than twice as much clopyralid
was absorbed by leaves than picloram by 4
hours after treatment (36). After 1, 3, and 8
days, more than three times as much clopyralid
was transported to the upper stem phloem as
picloram.

Leaves of spiny aster (Aster spinosus Benth.)
absorbed less 2,4-D and picloram than sun-
flower at 2, 4, and 6 hours after exposure (68).
Picloram concentration was usually less than 2,
4-D except after 4 hours exposure in spiny
aster leaves. Therefore, foliar absorption may
be the limiting factor in response of spring
broadcast applications of 2,4-D and picloram.
Absorption of the potassium salt of 2,4-D and
picloram by undisturbed stem tips compared to
regrowth stem tips was greater at 2 hours after
treatment but was usually no different at 4 and
6 hours (68). Main stems absorbed less herbi-
cide at 2 and 4 hours than undisturbed stem
tips but were no different at 6 hours after treat-
ment.

When 2,4-D and picloram absorption was
monitored in spiny aster from field applica-
tions, peak concentrations occurred in the
leaves at 24 to 48 hours after treatment and
declined up to 120 hours after treatment. Peek
concentrations from broadcast applications of
2,4-D at 2.24 kg ha"1 and of picloram at 1.12 kg
ha-l resulted in about 15 to 16 pg g'1 of herbi-
cide per gram fresh weight of spiny aster
leaves. There were usually no significant differ-
ences between herbicide concentrations in
shredded and nonshredded terminal stems. No

2,4-D or picloram wasdetected in rhizomes of
spiny aster.

In tissue culture, greatest absorption of piclo-
ram and dicamba in soybean and cottonwood
(Populus deltoides Marsh.) occurred from agar
the first Z4 hours after treatment (52). However
absorption remained nearly static for 14 days
thereafter. More dicamba was absorbed by soy-
bean and cottonwood tissue cultures than
either picloram or 2,4,5-T.

More picloram than triclopyr was absorbed
by greenhouse-grown huisache leaves by 3, 10
and 3O days following broadcast sprays applied
at 1.12 kg ha'1 (27). The potassium salt of piclo-
ram and the triethyamine salt of triclopyr were
used.

Detached leaves of Drummond's goldenweed
[Isocoma drummondii (T. & G.) Greene] absorb-
ed the potassium salt of 2,4-D from aqueous
solutions more slowly than did sunflower and
both species absorbed less of the potassium salt
of picloram than 2,4-D. There was no differ-
ence in absorption of herbicides by leaves 6
hours after exposure to solutions containing 0.5
percent (v/v) surfactant. Attached Drummond's
goldenweed leaves absorbed about 50 percent
available 2,4-D (diethylamine) and 25 percent
of available picloram (potassium salt) within 5
days after spraying in the field during July and
November.

Herbicide Formulation

Morton et al. (89) found larger amounts of 2,
4,5-T in honey mesquite leaves treated with the
butoxyethyl esters of 2, 4, 5-T than those treat-
ed with the ammonium salts. Concentra-tion of
2, 4, 5-T translocated to the stems, however,
was similar. Most data suggest that ester for-
mulations of the phenoxy herbicides penetrate
leaf surfaces more readily than amine salts
(63). This may or may not result in greater
accumulation of herbicide in the roots, since
the esters are not translocated as readily as the
amine salt formulations (29, 62).

Leaves of greenhouse-grown honey mesquite
rapidly absorbed triclopyr from both ester and
amine formulations (30). After 4 hours, about
23 percent of both formulations were absorbed
from application of commercial grade triclopyr.
By 24 hours after treatment, more triclopyr
acid was recovered from application of the
amine than the ester formulation. A large pro-
portion of the herbicide was absorbed by the

treated leaf, especially the amine formulation,
but not all the triclopyr was recovered after
transport because of possible degradation and
lack of analysis of the ester fraction. The tri-
ethylamine salt or the ethylene glycol butyl
ether esters of triclopyr were applied at 54 pg
and 62 pg, respectively, to one leaf per plant
per pot, on five plants, with four ‘replications.

In another study (30), the analytical grade of
the triethylamine salt and the n-butoxy ethyl
ester were applied to greenhouse-grown honey

\.w

mesquite leaves at 65 pg and 62 pg, respective- ,

1y, with five plants per replication and three
replications in a randomized complete block
design. After 0, 4, and 24 hours, absorption of
both forms were about equal when both the
acid and ester were analyzed and added togeth-
er for the ester. A majority of the ester was
rapidly hydrolyzed to the acid by 4 and 24
hours after treatment.

In field-grown honey mesquite (30), more tri-
clopyr acid (131 pg) was detected in leaves
after application of the amine than the ester
(39 pg) at 0 hours, but by 4 hours (105 vs. 110
pg) or 24 hours (54 vs 58 pg) no differences in
triclopyr formulations were apparent. Loss of
absorbed triclopyr from leaves was largely
caused by transport to the stern.

Application of the monoethanolamine salt
and the 2-ethylhexyl ester of clopyralid to
greenhouse-grown honey mesquite leaves with
a pipet indicated that about twice as much
clopyralid was absorbed within 15 minutes
from the ester form (26%) than from the amine
form (12%) of the total recovered (37). How-
ever, after 24 hours, absorption of the ester was
less than the amine. In another study (38),
treated leaves of greenhouse-grown honey
mesquite absorbed more clopyralid within 15
minutes (0 hours) after pipet application of the
oleylamine salt compared with the mono-
ethanolamine salt or the l-decyl ester. After 24
hours, treated leaves absorbed and transported
more clopyralid into the plant treated with the
salt formulations than the l-decyl ester.

Herbicide Mixtures

In greenhouse-grown mesquite, Davis et al.
(50) found that the uptake and transport of 2,
4,5-T decreased in the presence of picloram,
but the uptake and transport of picloram
increased in the presence of 2,4,5-T. Increasing
ratios of 2,4,5-T to picloram up to 16 to 1 con-

tinued t0 increase uptake and transport of
picloram. The inverse effect occurred for 2,4,
5-T when picloram: 2,4,5-T ratios were
increased.

Paraquat reduced absorption and transloca-
tion of picloram in greenhouse-grown honey
mesquite, huisache, and bean in 1 to 1 mix-
tures at 0.012 M each (50). In the field,
paraquat increased uptake of picloram by
yaupon (Ilex vomitoria Ait.) but did not effect
transport.

Bovey et al. (36) found that addition of piclo-
ram or triclopyr to clopyralid at equal rates
applied to field-grown mesquite (0.28 + 0.28
kg ha'1) increased clopyralid concentrations in
the leaves by 4 hours after treatment compared
with clopyralid applied alone.

Baur et al. (7) studied the absorption of
picloram and 2,4,5-T in detached live oak
(Quercus virginiana Mill.) leaves immersed in
aqueous solutions for up to 4 hours. Herbicide
concentration ranged from 103 to 10's M; solu-
tions were adjusted to either pH 4, 6, 7, or 8.
Absorption of picloram in the presence of
equimolar concentrations of 2,4,5-T exceeded
that for picloram alone. Picloram had no effect
on 2,4,5-T absorption.

Baur et al. (5) found that recovery of 2,4,5-T
as acid and ester was greater in live oak tissues
treated with mixtures of picloram (ester or salt)
than in tissue treated with 2,4,5-T as the 2-eth-
ylhexyl ester applied alone.

Carriers and Adjuvants

Fisher et al. (57) evaluated a wide range of
oils and oil-water emulsions as well as water as
2,4,5-T spray carriers for control of honey
mesquite. The diesel fuel oil-water emulsion
(1:3) was considered equally effective and more
economical to use than specially formulated
oils. In some instances, use of water alone as
the carrier reduced the effectiveness of the
2,4,5-T applications. Hull (62) indicated similar
results on velvet mesquite. A nontoxic oil in a
1 to 4 oil-water emulsion as a carrier for 2,4,5-
T resulted in considerably greater injury to the
nontreated distal foliage than diesel oil as a car-
rier. Behrens (14) found that when diesel fuel
alone was used as the carrier on greenhouse-
grown plants at spray volumes of 117 and 299
l ha'1, effectiveness was reduced compared
with 37 l ha-l. The reduced effectiveness was
attributed to the phytotoxicity of the diesel

fuel, which caused rapid killing of the leaves,
limiting 2,4,5-T translocation. However, Bovey
et al. (26) found that no differences occurred in
canopy reduction of honey mesquite when
water, diesel oil, or diesel oil and water carriers
at ratios of 1:3, 1:9, 1:18 were used with the
Z-ethylhexyl ester of 2,4,5-T in 187 l ha'1 dilu-
ent. Scifres et al. (94) found that absorption of
2,4,5-T ester was more rapid in a paraffin oil
carrier than in diesel fuel, water, or emulsions
of the oils in water carriers. No significant dif-
ferences in percentage mesquite control have
resulted from foam carriers (78, 97) compared
with conventional sprays or addition of sufac-
tants to the spray solution (26). Most commer-
cial herbicide formulations have sufficient sur-
factant and wetting properties for wetting plant
surfaces, and the addition of most sufactants or
emulsifiers to the spray solution may have lim-
ited effect.

Addition of surfactant I (trimethylnonylpoly-
ethoxyethanol) or surfactant II (4-isoprophenyl-
l-methyl-cyclohexane) at 1 and 0.6 percent
(v/v) of the spray solution enhanced the phyto-
toxicity of the triethylamine salt of triclopyr,
picloram, and the butoxyethanol ester of 2,4,5-
T in greenhouse-grown but not field-grown
honey mesquite (34). Adjuvants, however, did
enhance clopyralid activity (34, 36). Surfactant
I and II at 0.5 percent by volume enhanced
clopyralid absorption in field-grown honey
mesquite leaves by 4 and 24 hours after appli-
cation of broadcast sprays with 0.28 kg ha'1 of
clopyralid (36). Increased uptake of clopyralid
with surfactants may be partially due to
enhanced spray retention caused by the surfac-
tant (33, 34).

Organosilicone surfactants Sylgard 309 [2-(3-
hydroxypropyl)-heptamethyl trisiloxane, ethoxy-
lated, acetate EO glycol,-allyl, acetate] or Silwet
L-77 (polyalkyleneoxide modified polymethyl-
siloxane copolymers) added to the spray solu-
tion at 0.1, 0.25, 0.2, or 0.5 percent by volume
did not increase spray deposition, absorption,
translocation, or phytotoxicity of clopyralid in
greenhouse-grown honey mesquite (42).
Mayeux and Scifres (70) found 0.5 percent (by
volume) surfactant in the spray solution did not
enhance absorption of 2,4-D or picloram by
detached Drummond’s goldenweed leaves.
Mayeux and Johnson (76) indicated the addi-
tion of surfactant had little effect on absorption
of picloram in Lindheimer pricklypear (Opuntia
lindheimeri Engelm).

Meyer et al. (82) found that field-grown
honey mesquite leaves were functional in her-
bicide uptake for about 4 days after applica-
tion. However, maximum absorption apparent-
ly occurred the day of spraying. Thus, any
agent or force which causes leaf removal too
quickly after spraying reduces control. In most
cases, it is important to use a carrier that will
penetrate the waxy surface of the leaf but will
not kill the leaves or cause abscission soon
after spraying (95).

Spray Characteristics

Spray droplet size affects phytotoxicity
depending upon species studied. In some
species, herbicidal efficiency decreases as
droplet size increases above 500 micrometers
in diameter (63). Behrens (14) reported that
droplet size, spray volume, and herbicide con-
centration had no direct influence, other than
minor affects, on response of honey mesquite
or cotton to 2,4,5-T, but that droplet spacing of
465 droplets per cmZ was considered the maxi-
mum spacing that would maintain a high level
of herbicidal effectiveness.

The addition of surfactant WK (trimethy-
nonylpolyethoxyethanol) at 0.5 percent (by vol-
ume) of the spray solution caused increased
uptake of clopyralid by the upper canopy of
greenhouse grown honey mesquite (33).
Enhanced uptake after 24 hours was probably
a result of a twofold increase in deposit of
clopyralid on the plant (33, 40). Greater deposit
of clopyralid on plant surfaces after addition of
surfactant was associated with reduced liquid
surface tension and greater percentage of spray
volume in small droplets (< 204-pm diam.).
The addition of surfactant WK at 0.5 percent
(by volume) of the spray solution caused a
twofold increase in deposition of the mono-
ethanolamine salt of clopyralid but not the
oleylamine salt (40). There were no differences
in spray deposit between spray droplet size
spectrums of 160 or 330 pm Dv.5 or spray solu-
tion application of 47 or 187 l ha"1.

An air-assist spray nozzle at 9.4 l ha'1 by vol-
ume resulted in greater initial clopyralid
deposit and detection in the upper canopy of
greenhouse-grown honey mesquite than appli-
cation by conventional hydraulic nozzle at 9.4
or 187 l ha'1 (42). Air-assist application did not
increase phytotoxicity compared to hydraulic
nozzles. In the field, honey mesquite mortality
and canopy reduction were significantly less 16

months after aerial applications of clopyralid in
the 624 pm droplets treatment in two of four
experiments, when compared with plots treat-
ed with smaller droplet sizes (325 and 475 pm
Dv.5) (104). Mortality increased with larger
spray volumes (19, 37, and 75 l ha'1) particular-
ly with 625 11m droplets. Mortality data show
that larger droplets sizes require larger spray
volumes for greatest efficiency.

Hand carried spray equipment with 800067,
8001, and 8015 Spraying Systems flat fan noz-
zles were used to obtain 37 , 187 and 935 1 ha'1
in a diesel oil-water 1:3 (v/v) ratio (26). Diluent
of 187 l ha'1 produced a greater canopy reduc-
tion than either 37 or 935 l ha") in honey
mesquite, winged elm, and Macartney rose
(Rosa bracteata ]. C. Wendl.) using the ester
form of 2,4,5-T at 0.56 and 2.2 kg ha"1 on
honey mesquite and winged elm and 2.2 kg
ha-l of 2,4-D ester on Macertney rose. When
1.1 kg ha"1 of MCPA was used on white brush,
there were no differences in 37,187 or 935
l ha"1 diluent but 187 l ha-l of diluent was
superior to other spray volumes on live oak
using 2.2 kg ha"1 of 2,4,5-T. A diluent volume
of 37 l ha-l may have resulted in insufficient
coverage for maximum herbicide uptake for
most species when ground equipment was
used, whereas 935 1 ha-l may have resulted in
loss of the herbicide from plant surfaces
through excessive runoff, except with live oak.

pH Affects

Uptake of 2,4,5-T-1-14C by honey mesquite
leaflets immersed in solutions rapidly dimin-
ished as pH was increased from 3.5 to 9.5 in
the treating solution (11). Leaves treated with
droplets at pH 3.5 and kept moist absorbed
about 92 percent of available 2,4,5-T-1-14C dur-
ing the first 3 hours of exposure, with no addi-
tional uptake for the next 2 hours. Comparable
leaflets treated with droplets that were allowed
to evaporate absorbed only 30 percent of avail-
able 2,4,5-T-1-14C during the first 3 hours and
an additional 10 percent the next 2 hours.
Leaflets continued to absorb 2,4,5-T-1-14C for
about 14 to 24 hours after treatment with pH
3.5 droplets that were allowed to evaporate,
but those kept moist did not absorb 2,4,5-T-1-
14C after 3 hours, presumably because of lack
of available 2,4,5-T-1-14C. Uptake under dry
conditions from pH 7.5 and 9.5 droplets con-
taining 1 M N H4 Cl was equivalent to uptake
from pH 3.5 and 5.5 droplets lacking NH4 C1.
NH4 C1 had no enhancing effect on uptake at

any pH when leaflets were immersed or
droplet-treated and maintained moist. Low con-
centrations of urea had no enhancing effect on
uptake at pH 9.5 by droplet-treated leaflets that

.Q were allowed to dry. Urea concentrations above

0.1 M inhibited uptake.

Discs of potato (Solarium tuberosum L.) tuber
tissue were immersed in buffered (pH 4.0 to
8.0) solutions of picloram (5X1O'4 M to 5x103
M) for 1 to 36 hours (100). Uptake of picloram
during incubation, and leakage after return of
the discs to untreated buffer, were determined
by gas chromatographic analysis of extracts of
the tissue and ambient buffer. Picloram absorp-
tion increased with concentration and with
time up to 24 hours. Maximum uptake
occurred at pH 4.0 and very little picloram was
absorbed at pH 7.0 and 8.0. Both absorption
and leakage were temperature dependent. The
rate and extent of leakage was greatest at the
highest concentration. Typically, more than 90
percent of the picloram absorbed from a 5x103
M solution was lost to fresh buffer within 12
hours.

Detached live oak leaves were immersed in
aqueous solutions of picloram or 2,4,5-T acid
for periods up to 4 hours. (7). Herbicide con-
centration ranged from 103 to 10-6 M; solutions
were adjusted to either pH 4, 6, 7, or 8. More
2,4,5-T was absorbed at pH 4 than pH 6, 7, or
8 at concentration of 103 M solutions. More
picloram was absorbed at pH 4 and 6 than pH
7 or 8. Under laboratory conditions, weak acids
penetrate best at low pH values where the mol-
ecules are largely in the undissociated form
(44,46). In this state, they more readily pene-
trate the lipoidal phases of the cuticle and leaf
cells. However, under field conditions, little
benefit of improved control has been shown by
adjusting pH of the spray solution.

Mayeux and johnson (76) found that absorp-
tion decreased with increasing pH of the piclo-
ram solution in detached pricklypear pads indi-
cating that picloram diffused through the cuti-
cle as the undissociated molecule.

Air Temperature and
Relative Humidity

Morton (88) treated honey mesquite seedling
leaves with 5 to 10011g of carboxyl-labeled
2,4,5-T and found more 2,4,5-T absorbed at 38
C than at 21 or 29 C after 72 hours. Approxi-
mately 50 percent of the 2,4,5-T applied to a
single leaf was absorbed. Only slight differ-

ences in absorption were found at different
humidity levels. Baur et al. (11), however, sug-
gested that humidity effects are of more impor-
tance in foliar application than are pH effects
since uptake of 2,4,5-T 14C by honey mesquite
leaflets under high-humidity surpassed uptake
under low-humidity conditions.

Rainfall

Bovey and Diaz-Colon (19) found that oil-sol-
uble formulations (esters) of Z,4,-D, 2,4,5-T,
and picloram were less affected by artificial
rainfall than water-soluble herbicides such as
paraquat and cacodylic acid on guava (Psidium
guajava L.) and mango (Mangifera indica L.).
The oil-soluble phenoxy herbicides usually
retained their effectiveness even when leaves
were washed within 15 minutes after treat-
ment. Field-grown honey mesquite leaves
showed complete leaf necrosis even when
leaves were washed 20 minutes after treatment
with paraquat, indicating rapid absorption (16).
Winged elm and live oak showed little injury
under the same conditions but both showed
about 40 percent leaf necrosis when washed 60
minutes after treatment.

The foliar activity of the amine salts of
glyphosate, dicamba, picloram, clopyralid, and
triclopyr was decreased on greenhouse-grown
huisache when simulated rainfall was applied
up to 240 minutes after herbicide treatment
(39). The effectiveness of the butoxyethyl ester
of triclopyr or 2,4,5-T was not reduced by rain-
fall washoff within 15 minutes after applica-
tion. In natural huisache stands, injury from
triclopyr ester or amine salts of picloram or
clopyralid was not reduced by simulated rain-
fall at 60 minutes after herbicide treatment. In
the greenhouse and field, honey mesquite
leaves rapidly absorbed most herbicides and
triclopyr, 2,4,5-T, picloram, and clopyralid were
highly phytotoxic even when simulated rainfall
was applied within 15 minutes after herbicide
treatment (39).

Time of Day

No absorption data are available for huisache
or Macartney rose relative to time of day or
season of application. However data suggested
that l to l ratios of picloram plus 2,4,5-T as the
triethylamine salts were more effective when
applied to these woody plants in the evening
(6:00 p.m.) than morning (6:00 a.m.) or midday
(1:30 p.m.) (24). Best control of huisache was in

June while best control of Macartney rose
occurred in September and October. Poorest
control occurred when internal water stress
was highest.

Moisture Stress

Merkle and Davis (80) showed that foliar
absorption of 2,4,5-T and picloram in beans
(var. Black Valentine) was unaffected by
extreme moisture stress. Moisture stress
reduced foliar uptake of picloram in honey
mesquite but not in winged elm (48). Moisture
stress did not affect absorption of 2,4,5-T in
honey mesquite or winged elm.

Bovey and Clouser (41) found in preliminary
studies that water stress (-1.3 to -2.8 MPa) did
not affect absorption and translocation of
clopyralid in greenhouse-grown honey
mesquite 4 or 24 hours after herbicide treat-
ment. Addition of triclopyr (synergistic to
clopyralid) increased clopyralid uptake at low
water stress (-1.3 MPa) but at high water stress
(-2.8 MPa) triclopyr decreased clopyralid
uptake.

Light

Light assists herbicidal penetration by stimu-
lating stomatal opening in most species (1).
Measurement of herbicide absorption by honey
mesquite as influenced by quality and intensity
of light has not been determined. Brady (15),
however, found that the absorption of the
isooctyl ester of 2,4,5-T increased as light
intensity increased up to 2,680 foot candles,
but it decreased thereafter in post oak (Quercus
stellata Wangenh.) and water oak (Quercus
Nigra L.). Absorption of 2,4,5-T increased as
light intensity increased up to 4,000 foot can-
dles in long leaf pine (Ilex opaca Ait.). Davis et
al. (49) found that uptake of picloram by live
oak leaves decreased as light intensity
increased.

Scifres et al. (96) found that honey mesquite
seedlings which developed under shade were
more easily killed by 2,4,5-T sprays than
seedlings grown in sunlight. The increased
effectiveness under shade may have been
caused by limited cuticle development (64) and,
thus, greater herbicide uptake. Baur and
Swanson (3) found that honey mesquite grown
during short days was more susceptible to
2,4,5-T or picloram than that grown during
long days. The reason for this difference is not

clear but may be related to cuticular develop-
ment.

Leaf Structure and Development

As indicated earlier, the best time for appli-
cation of foliar herbicides for honey mesquite
control is during a 50- to 90-day period after
the first leaves emerge in the spring. By May
20, leaflets of honey mesquite in Brazos
County have usually attained full maturity (81).
The upper cuticle is usually 5 to 8 microns
thick and the lower cuticle is usually 2 microns
thick; however, penetration of cuticle by herbi-
cides appears sufficient for herbicidal effect
and translocation to other parts of the plant. In
most plants, there is a relationship between
cuticular development and composition and
foliar absorption of herbicides (64). The more
mature the leaf, the greater the cuticular devel-
opment, and that may partially explain the
resistance of honey mesquite to herbicide
sprays applied late in the growing season, even
though limited stomatal penetration can occur
when cuticules become very thick (64).
Mayeux and Jordan (74) found that amounts of
epicuticular wax per unit leaf area on honey
mesquite leaves were least in April and May,
increased until July, and remained stable there-
after at several locations in Texas. Population
means ranged from ca 4 mg dm'2 in east-cen-
teral Texas during April and May to a maxi-
mum of over 10 mg dm'2 on leaves of trees
growing in north-centeral Texas in October.
Honey mesquite growing in arid-west Texas
and semiarid south Texas had no more wax per
unit leaf weight or area than those in humid
east-central Texas. Mayeux and Wilkerson (77)
also determined the chemical composition of
epicuticular wax on honey mesquite. Jacoby et
al. (65) studied wax on leaves of honey
mesquite in northeastern Texas. They found
trends similar to Mayeux and jordan in wax
accumulation on honey mesquite leaves but
found considerable variation in wax accumula-
tion among individual trees. jacoby et al. (65)
further stated that increasing amounts of epicu-
ticular wax on the leaves of honey mesquite
during early summer may contribute to
increasing resistance to foliar-applied herbi-
cides.

Wax thickness on honey mesquite may act as
a herbicide barrier, but data indicate that most
herbicides used are rapidly absorbed and trans-
ported by honey mesquite leaves (11, 28, 30,

31, 32, 33, 35, 36, 37, 38, 39, 41, 48, 49, 56, 62,
88, 94, 107)). Bovey et al. (31) found that con-
centrations of 2,4,5-T, triclopyr and picloram in
upper stem pholem and Xylem 3 days after
treatment t0 be greater in early May 0r late
April than late May, June, July, August, or
September but differences were not always sig-
nificant. Control with 2,4,5-T, picloram, and
triclopyr declined in July, August, and
September (87) but is related to anatomical and
physiological changes in honey mesquite plants
instead of leaf wax accumulation (81). Meyer et
al. (87) and Jacoby et al. (66) reported success-
ful late season application with clopyralid on
honey mesquite. Data on clopyralid concentra-
tions in honey mesquite in upper stem phloem
and Xylem 3 days after treatment over a 2-year
period showed no differences among dates of
sampling (31). Higher than normal rates were
used (1.1 kg ha'1 versus 0.28 or 0.56 kg ha"1) .
Mayeux et al. (68) indicated that poor herbicide
uptake by spiny aster top-growth was not ade-
quately explained by cuticle thickness but that
chemical characteristics of the epidermal cover-
ing may be more responsible for high resis-
tance to herbicide penetration than cuticle
thickness. Large quantities of viscous, non-crys-
tilline epicuticular waxes were observed on
leaves of three goldenweed (Isocoma) species
('72). Wax on leaves of field-grown plants of the
least herbicide-susceptible species, common
goldenweed [I. coronopifolia (Gray) Greene],
increased from 71 mg dm"2 in March to 286 mg
dm'2 in October. This was two to four times
greater than the amount present on other gold-
enweed species or Drummond's goldenweed [I.
drummondii (T. & G.) Greene] and jimmyweed
[I. Wrightii (Gray) Rydb.]. Greenhouse-grown
plants produced quantities similar to field-
grown plants, but maximum production
occurred during summer months. Wilkerson
and Mayeux (105) determined that the chemi-
cal composition of epicuticular wax of I.
coronopifolia and I. drummondii was 85 to 95
percent free fatty acid and alcohols. Alkane

(< 5 percent), ester (< 2 percent) and ketone
(< 3 percent) concentrations were low. The
short-chain, free fatty acids and alcohols sug-
gested that they are hydrophilic compared with
other plants»; and helps explain the observed
loss of epicuticular waxes in rainfall (71, 75)
and variation in responses of these weedy
shrubs to herbicide sprays (67, 69, 73). Control
of I. coronopifolia and I. drummondii with
broadcast sprays of translocated herbicides

strongly depends upon substantial rainfall prior
to treatment (71). Removal of leaf waxes
increased picloram accumulation in detached
leaves of both species by a factor of eight,
demonstrating that these deposits effectively
reduce herbicide entry (69). Mayeux and
Johnson (76) found that removing the epicutic-
ular wax from mature pads (cladophylls) of
Lindheimer pricklypear cactus increased piclo-
ram absorption by four-to six fold while addi-
tion of surfactant had little effect on absorp-
tion. Picloram entered detached pads at the
areoles more readily than through the sur-
rounding cuticle. New pads absorbed more
picloram than old pads. Most of the picloram
remained in the waxy surface of old and new
pads. About 2 percent of applied picloram was
recovered from within the epicuticular wax
after 3O days. Little picloram was absorbed by
roots. Wilkerson and Mayeux (106) determined
that 97 percent of total epicuticular wax of Q.
engelmanii was alkanes and esters on green-
house-grown cladoyphylls. The most prevalent
carbon numbers of alkanes from buds were C15
through C25 while those of fully expanded
cladophylls were C29 through C35. Both odd
and even numbered ester components were
present.

The abaxial (lower) surface of the leaf usual-
ly absorbed more herbicide than the adaxial
(upper) surface using picloram or 2,4,5-T on 10
species of woody plants (49). Absorption
through leaf surfaces varies from abaxial to
adaxial on the same species and between
species. Meyer and Meola (85) have provided
data on leaf and stem surfaces of many Texas
woody plants.

Metabolism Degradation and
Mode of Action

Morton (90) found that approximately 80
percent of the 2,4,5-T absorbed by leaves of
honey mesquite seedlings was metabolized
after 24 hours. Metabolism was completely
inhibited at 10 C, and a lower rate of metabo-
lism was noted at 38 C than at 21 C and 29 C.
Picloram, however, is more resistant to degra-
dation in plants than 2,4,5-T (22).

The effects of picloram on protein synthesis
in bean (var. Astro) hypocotyl and hook tissues
were studied (8). Picloram (104 M) was shown
to have a stimulatory effect on 14C-1-DL-
leucine uptake in hook but not hypocotyl tis-
sues. Maximum leucine incorporation and max-

imum total protein concentration occurred in
hook tissues treated with 104 M picloram.
Inhibition of protein synthesis with cyclohex-
imide (CH) and erythromycin (ERY) indicated
that endogenous and picloram-stimulated pro-
tein synthesis is a function of the 80S cytoplas-
mic ribosomes rather than 70S chloroplast or
mitochondria ribosomes.

Gas chromatographic and radioisotopic
analyses were made of cell wall, chloroplast,
mitochondria, and the remaining cytoplasm
fractions of cowpea (Vigna sinensis Endl. var.
Southern Blackeye) trifoliates acropetal to pri-
mary leaves treated with the growth regulator
picloram (9). The majority of picloram was
recovered from the remaining cytoplasm.
Concentrations in chloroplasts and mitochon-
dria were consistently low.

Pretreatment of potato (Solarium tuberosum
L., var. Russet) tuber discs in pH 5.5 buffer sig-
nificantly reduced uptake of picloram (103 M )
(6). Tissue pretreated in buffer at 7 C subse-
quently absorbed more picloram than tissue
pretreated at 25 C. Inclusion of cetyl trimethyl
ammonium bromide (CTAB) (2x10"4 M) in the
treating solution caused a significant increase
in picloram uptake in tissues that were not pre-
treated in buffer. The reduction in uptake
caused by buffer pretreatment was effectively
reversed when CTAB was included in the treat-
ing solution. The results suggest that picloram
uptake by potato tissue is related to the avail-
ability of the quaternary ammonium binding
sites provided by membrane phosphatides.

In nutrient agar, comparative concentrations
(103 to 105 M) of 2,4,5-T generally inhibited
the growth of tissue cultures of soybean (var.
Acme) and cottonwood more than either piclo-
ram or dicamba (52). Compared to untreated
tissue, dicamba or picloram at 106 M in the
nutrient agar resulted in a 200 percent increase
in the growth of soybean tissue. At 105 and
105 M dicamba also produced an increase in
the growth of cottonwood tissue. Greatest
absorption of picloram and dicamba by tissue
cultures from agar occurred during the first 24
hours after treatment. However, absorption
remained nearly static thereafter for 14 days.
More dicamba was absorbed by soybean and
cottonwood tissue cultures than either picloram
or Z,4,5-T. In another study (23), mixing
equimolar solutions of 2,4,5-T plus dicamba,
2,4,5-T picloram, or picloram plus dicamba at
104, 106, and 10's M did not increase phytotox-

1O

icity over that of the most phytotoxic herbicide
of the pair.

We studied changes in the concentration of
picloram with time in roots, stems, and leaves
of 20-day-old seedlings of huisache and honey
mesquite (4). Exposing root systems to aqueous
solutions of picloram (1.0 ppm on huisache and
10.0 ppm on honey mesquite) for 24 hours
killed approximately 60 percent of the treated
plants. In honey mesquite, picloram was redis-
tributed and eventually lost over a 5-day peri-
od, whereas neither redistribution nor loss
occurred in huisache.

Honey mesquite leaves absorbed large
amounts of clopyralid as foliar sprays by con-
centrations of 10 11g or more of the herbicide
per gram (fresh wt) of the basal stem phloem
by 4 days after treatment. (35). Small quantities
of clopyralid (< 1 11g g1) were detected in basal
stem phloem after spray applications of clopy-
ralid to defoliated plants or roots of foliated
plants treated by soil application. When
applied to foliated plants, the 0.56 kg ha'1 of
clopyralid killed 60 percent or more of the
plants, but none were killed when clopyralid
sprays were applied to defoliated plants or
when 2.2 kg ha"1 of clopyralid was applied to
the soil. Water, diesel oil plus water, or water
plus surfactant were equally effective as clopy-
ralid carriers as foliar sprays.

Translocation

Once an herbicide is absorbed by leaves and
stems, a key factor in killing woody plants is
translocation of the phytocide to the stem and
roots. The phloem is the principal food-con-
ducting tissue in vascular plants. Compounds
like 2,4-D are translocated through the phloem
from regions of carbohydrate synthesis (leaves)
to sugar importing tissues such as roots, buds,
shoot tips, seeds and fruit, and other leaves.
The direction of herbicide movement is deter-
mined by the patterns of food distribution and
utilization within the plant, since translocation
of food may also occur from roots to leaves or
between other plant parts (44, 45, 46, 47).
Ideally, at least for the phenoxy herbicides, it is
best to apply foliar sprays when food transport
is occurring form the leaves (basipetal) to other
plant parts (roots) so as much herbicide as pos-
sible is translocated to the base of the stem and
roots. In the case of honey mesquite, this
occurs under springtime conditions after
foliage is mature enough to export sugars and

the plant is rapidly growing radially. If the her-
bicide is applied at other times during the year,
results may be unsatisfactory since assimilate
(food) movement may be limited. For success-
ful chemical control of honey mesquite, move-
ment of phytotoxic materials to regenerative
tissues (buds) is necessary to eliminate their
growth potential. The greatest concentration of
buds occurs on the trunk in the first 3O cm
below the soil line (53, 57, 58, 81, 95).

Herbicide Type

Fisher and Young (54) reported in 1948 that
sodium arsenite, sodium arsenate, sodium chlo-
rate, ammonium sulfamate, sulfamic acid,
ammonium thiocyanate, 2,4-D, and 2,4,5-T
were the only chemicals out of several hundred
tested that were absorbed by the foliage and
translocated in sufficient amounts to kill dor-
mant buds on the underground stems of honey
mesquite. Increasing chemical concentrations
did not improve translocation. In 1949, Young
and Fisher (108) reported that the ester of
2,4.5-T was a more effective treatment than
several formulations of 2,4,-D or other chemi-
cals.

Rapid transport of 2,4,5-T was determined
by plant response after spraying an exposed
branch of honey mesquite and observing the
effect on leaves of sprayed compared with a
shielded or protected plant part. (107). Fisher
and Young (88) also used a tip immersion
method to test translocation by immersing the
tip of a branch into a container of herbicide for
periods of 1 to 24 hours and observing translo-
cation by plant response. These methods were
very useful in determining the most effective
transported herbicides but did not quantitively
measure herbicide content in plant tissue.

Early in the 1960s, picloram and dicamba
were discovered to be effective herbicides for
controlling honey mesquite and other woody
plants. Triclopyr and clopyralid were evaluated
as substitute herbicides for 2,4,5-T in the late
1970s, 1980s and 1990s (32).

Merkle and Davis (79) recovered 76 percent
of the 2,4,5-T and 94 percent of the picloram
from bean plants (Black Valentine) 4 hours
after application to a primary leaf. Most of the
2,4,5-T and picloram was found in the treated
leaf and leafwash but small quantities of piclo-
ram was detected throughout the plant includ-
ing the roots. Probably considerable metabo-

11

lism of 2,4,5-T occurred since recovery was
only 76 percent (88). Data are similar in honey
mesquite seedlings to beans in that mesquite
absorbed piclorams more readily and exten-
sively than 2,4,5-T (48). After 4 hours, the apex
contained both herbicides but only picloram
occurred in roots. After 24 hours, the apex and
roots contained more picloram than 2,4,5-T.
The amounts of picloram and 2,4,5-T absorbed
and transported in winged elm were similar.

In the field, Davis et al.(51) found that
2,4,5-T content in honey mesquite stem
phloem was higher in stems within 20 cm of
the foliage than those near the soil line 48
hours after treatment. Similar levels of 2,4,5-T
occurred from application of either 0.56 or 1.12
kg ha-l whereas, three times as much picloram
occurred in plants treated with 1.12 kg ha'1
than with 0.56 kg ha"1. Herbicide concentration
was highest in June and lowest in August.

Meyer et al. (82) indicated the time required
by herbicides to be retained on the plant after
spraying to give maximum canopy reduction or
mortality varied among greenhouse-grown
honey mesquite, huisache, and whitebrush
[Aloysia gratissima (Gillies & Hook.) Troncoso]
and field-grown honey mesquite, huisache,
whitebrush, live oak, Arizona ash (Fraxinus
velutina Torr.), and winged elm. In most
species, however, herbicide absorption and
transport were complete within a 4-day period
or less as compared to undefoliated treated
plants.

Bovey and Mayuex (28) studied the effective-
ness and transport of 2,4,5-T, picloram, tri-
clopyr, and clopyralid in greenhouse-grown
honey mesquite. Higher concentrations of
clopyralid than 2,4,5-T, triclopyr, or picloram
usually were found in honey mesquite stems
and roots 3, 10, and 30 days after application
to soil, foliage, or both. This may be one reason
why clopyralid is highly effective in controlling
honey mesquite. In other studies, concentra-
tions of clopyralid and picloram in upper-stem
phloem were not different 4 hours after treat-
ment, but clopyralid concentrations were sig-
nificantly higher than picloram at 1, 3, and 8
days after treatment in greenhouse-grown
honey mesquite (36).

In the field and greenhouse, Bovey et al. (28,
31) found comparisons of triclopyr, 2,4,5-T,
picloram, and clopyralid similar to studies by
Davis et al.(51) who compared picloram and

2,4,5-T on honey mesquite. More clopyralid
than 2,4,5-T, triclopyr, or picloram was usually
detected in upper and basal stem phloem and
xylem. Concentrations of 2,4,5-T and triclopyr
in stem tissue were usually < 2 pg g1 fresh wt,
regardless of date of application. Concentra-
tions of picloram or clopyralid were as high as
11 and 22 pg g1 fresh wt, respectively, in
upper stem phloem at some dates of applica-
tion. Higher concentrations of all herbicides
were detected in upper stem phloem than in
upper stem xylem or basal stem phloem or
xylem. More herbicide tended to be detected
in stems when herbicides were applied early
(May and June) than late (August and Septem-
ber) in the season. Concentrations of triclopyr
and picloram diminished about 25 percent
from 3 to 3O days after treatment, whereas,
concentrations of 2,4,5-T and clopyralid
diminished about 5O percent for the same
time period.

Bovey et at. (17) found that soil applications
of picloram were more effective on green-
house-grown huisache than foliar treatments.
However, soil and foliar applications at 0.56 kg
ha"1 were lethal on foliated plants whereas
hand defoliated plants showed considerable
regrowth. Plants treated with 0.28 kg ha"1
required 24 hours before leaf removal for maxi-
mum herbicide effectiveness. Concentration of
picloram in roots from soil and foliar applica-
tion was similar. Absorption and movement
studies showed that 24 hours were required to
move lethal amounts of picloram into stem and
root tissues of huisache after foliar treatment.

Further research by Bovey et al. (27) indicat-
ed that more picloram than triclopyr was found
in greenhouse-grown huisache up to 3O days
after treatment as soil, foliar, or soil plus foliar
treatments. Picloram also showed greater herbi-
cidal activity.

Mayeux (68) found spiny aster absorbed little
herbicide relative to that in annual sunflower.
Spiny aster absorbed and transported more 2,4-
D than picloram when applied as the potassi-
um salts of both herbicides by 4 and 6 hours
after treatment. In general, 2,4-D behaved simi-
larly when applied to leafless spiny aster in
June and to foliated spiny aster in March.
Concentration of 2,4-D in terminal stems of
regrowth 74 days after shredding rose rapidly
to almost 19 pg g1 fresh wt at 24 hours after
application and gradually fell to about 5 pg g1
after 120 hours. Maximum 2,4-D concentration

12

in terminal stems of undisturbed spiny aster
was less than 14 pg g1. Picloram concentra-
tions in terminal stems were highly variable.
There were no differences in herbicide concen-

i trations in shredded and nonshredded terminal

stems. No 2,4-D or picloram was detected in
rhizomes.

Drummond's goldenweed leaves absorbed
about 5O percent of available 2,4-D (diethy-
lamine) and 25 percent of available picloram
(potassium salt) within 5 days after spraying in
the field during July or November (70).
Herbicide accumulation in Drummond's gold-
enweed taproots after spray applications was
generally slow, regardless of season, but
translocation to taproots was substantially
greater after application in November than
after treatment in March or July. Accumulation
of picloram in taproots was faster and more
extensive than accumulation of 2,4-D. How-
ever, based on mortality at 6 months after
treatment, both herbicides were translocated in
quantities adequate for control. The greater
effectiveness of picloram, despite its low foliar
uptake, than 2,4-D is attributed to its greater
mobility and root uptake in Drummond's gold-
enweed after broadcast sprays.

More picloram was translocated basipetally
from treated new pricklypear pads to untreated
old pads than in the opposite direction, but
concentrations in untreated pads were low
(< 1 pg g1) (76). Little picloram was absorbed
by roots, compared with pads, and little was
translocated into or out of roots. These results
conflict with the view that the effectiveness of
picloram for pricklypear control is attributable
to extensive root uptake and acropetal trans-
port. However, observations of plants 6 months
after treatment indicated that soil applications
were more effective than sprays in the
glasshouse.

Herbicide Formulation

Although Morton et al. (89) found larger
amounts of 2,4,5-T in honey mesquite leaves
treated with the butoxyethyl ester than the
ammonium salt, concentrations of 2,4,5-T in
the stem were equal. Hull (62) reported in vel-
vet mesquite that when carried in a nontoxic
oil emulsion, the free acid, the triethylamine,
and the sodium salts of 2,4,5-T all demonstrat-
ed a greater tendency to be translocated to
more distant portions of the plant than did
ester formulations. Tschirley and Hull (101),

however, found the ester of 2,4,5-T consistently
more effective than the amine formulation on
velvet mesquite under field conditions.
Research data of Fisher et al. (57) on honey
mesquite agree with that of others (101) in that
the low volatile esters and suspended acids
were more consistent in killing mesquite than
either the high volatile esters or the amine for-
mulations. The reasons for the superior perfor-
mance of the ester of 2,4,5-T over the amine
formulation has not been clearly established,
but the ester formulation probably penetrates
the wax and cuticle on the leaf more readily
than the amine. However, Beck et al. (12,13)
showed little difference in effectiveness
between the ester and amine formulations of
2,4,5-T on honey mesquite. Differences in for-
mulation may have been masked by high rate
of application or by the fact that sprays were
applied to the base of the plants.

Bovey and Mayuex (28) found no differences
between the ethylene glycol butyl ether esters
or triethylamine salt of triclopyr in greenhouse-
grown honey mesquite stems and roots 3,10,
and 3O days after aqueous applications to the
soil, foliage, or soil plus foliage.

In other detailed studies, triclopyr was rapid-
ly transported from the treated leaf to other
plant parts. Triclopyr concentrations recovered
4 hour after treatment in the upper canopy,
lower canopy, and roots averaged 0.12, 0.19,
and 0.09 pg, respectively (30). Concentrations
of triclopyr recovered after 24 hours were not
significantly different than after 4 hours in the
canopy. No ester from ester application was
recovered in the canopy, other than that in the
treated leaf. Uptake and transport of triclopyr
applied as either the ester or the amine 4 and
24 hours after treatment were similar. Triclopyr
recovered from stems of honey mesquite in the
field ranged from 0.16 to 0.72 pg g1 in phloem
and from 0.04 to 0.20 pg g1 in xylem from a
broadcast spray application of the butoxyetha-
nol ester at 1.12 kg/ha'1. Concentrations of tri-
clopyr were usually not significantly different
in either the upper or lower stems whether
sampled 3 or 30 days after treatment.

Foliar sprays of the monoethanolamine salt,
potassium salt, free acid, and l-decyl ester of
clopyralid were more effective in killing green-
house-grown honey mesquite than the 2-ethyl-
hexyl ester at rates of 0.28 kg ha-l or less (37).
More clopyralid was transported to the lower
canopy from application of the monoethanola-

l3

mine salt and potassium salt than the 2-ethyl-
hexyl ester of clopyralid at 4 hours or 1, 3, or 8
days after treatment. Application of the mono-
ethanolamine salt and the 2-ethylhexyl ester to
leaves with a pipet indicated that about twice
as much clopyralid was absorbed within 15
min from the ester form (26 percent) than from
the amine form (12 percent) of the total recov-
ered. However, after 24 hours, absorption of
the ester was less than the amine. More than
twice as much clopyralid was transported from
the treated leaf after application of amine than
the ester. Only the acid form of clopyralid was
transported away from the site of application of
either ester or amine.

Foliar sprays of the monoethanolamine salt,
oleylamine salt, and l-decyl ester of clopyralid
were about equally effective in killing green-
house-grown honey mesquite (38). Treated
leaves absorbed more clopyralid within 15 min
after pipet application of the oleylamine salt
compared with the other formulations. After 24
hours, treated leaves had absorbed and trans-
ported more clopyralid into the plant from the
salt formulations than the l-decyl ester. There
were no consistent differences among clopy-
ralid formulations in transport of clopyralid
from foliar sprays at 4 hours or 1, 3, or 8 days
after treatment. Only the acid form of clopy-
ralid was transported from the site of applica-
tion of either ester or the amine formulation.

Herbicide Mixtures

The combination of picloram and 2,4,5-T
(18, 92) was particularly useful in honey
mesquite control. Davis et al. (50) in 1968
found that transport of picloram to the lower
stern in greenhouse-grown honey mesquite was
increased in the presence of 2,4,5-T whereas
the uptake and transport of 2,4,5-T was
decreased in the presence of picloram.
Increasing ratios of 2,4,5-T to picloram in mix-
tures up to 16 to 1 continued to increase
uptake and transport of picloram; the reverse
effect occurred for 2,4,5-T when 2,4,5-T to
picloram ratios were decreased. More total her-
bicide was transported when the 2,4,5-T and
picloram combination was used than either
herbicide used alone at equal rates. This may
help to explain the greater effectiveness of the
herbicide combination in controlling honey
mesquite. When paraquat was combined with
picloram on honey mesquite, huisache, and
bean, transport of picloram to the lower stem

was reduced because of damage of the trans-
port system by paraquat.

In field studies, Davis et al. (51) found that
highest concentrations of 2,4,5-T, picloram, or
combinations of 2,4,5-T and picloram in
phloem were associated with dates of best con-
trol of honey mesquite established by numer-
ous investigations. Adding 2,4,5-T to picloram
caused an increase in the amounts of picloram
in the phloem in four of five dates of applica-
tion (51). These data agree with the laboratory
and greenhouse investigations previously
described (50). Therefore, the combination of
picloram and 2,4,5-T was generally more effec-
tive than either herbicide applied alone.

Recovery of 2,4,5-T as the acid and ester was
significantly greater in live oak tissues treated
with mixtures of the 2-ethylhexyl ester of 2,4,5-
T (2.2 kg ha"1) plus the potassium salt or
isooctyl ester of picloram (0.56, 1.1, and 2.2 kg
ha-1) than in tissues treated with 2,4,5-T ester
alone (5). Recovery of 2,4,5-T as the ester was
noted in the middle and lower-stem tissues.
Between 9O and 99 percent of the herbicide
recovered 1 month after treatment was gone 6
months after treatment. Evaluation of brush
reduction 2 years after treatment indicated that
mixtures of picloram salt and 2,4,5-T resulted
in greater reduction of brush than mixtures of
picloram ester and 2,4,5-T or 2,4,5-T alone.

Bovey et al. (36) found that the addition of
picloram or triclopyr to clopyralid at equal
rates (0.28 +0.28 kg ha"1) increased clopyralid
concentrations in field-grown honey mesquite
by 1 day after treatment compared to clopy-
ralid applied alone.

Carriers and Adjuvants

A large number of diluents and adjuvants for
herbicides have been evaluated for control of
woody plants with some success (26, 32, 57,
62) as discussed in the Carriers and Adjuvants
section under Foliar Absorption.

An April application of 1.12 kg ha"1 or piclo-
ram plus 5.0 percent X-77 plus 10.0 or 25.0
percent of DMSO produced more effective
canopy reduction of yaupon 1 year after treat-
ment than did other herbicide treatments or
dates of treatment (10). Increased canopy
reduction by retreatment the second year sug-
gests that X-77 rather than DMSO was the
effective component in the spray mixtures.

14

Scifres et al. (94) compared water, diesel oil,
diesel oil and water emulsion (1:4), paraffin oil,
and paraffin oil and water emulsion (1:4) for
carriers of 0.56 kg ha"1 of the butyl ether ester
of 2,4,5-T in greenhouse-grown honey
mesquite. No differences related to carrier
occurred in the amount of 2,4,5-T translocated
to the stem and roots, although greater
amounts of herbicides were absorbed by leaves
treated with diesel or paraffin oil carriers.

Concentration of clopyralid in basal stem
phloem of field-grown honey mesquite sampled
4 and 30 days after spraying 0.56 kg ha"1 to the
foliage showed no differences in water, diesel
oil plus water (114 v/v), and water plus 0.5 per-
cent surfactant (v/v) diluents (35). Surfactant I
(trimethylnonylpolyethoxyethanol) or surfactant
II (4-Isopr0phenyl-1-methyl-cyclohexane) at 0.5
percent by volume of the spray solution
enhanced clopyralid absorption and transport
to the upper stem phloem in field-grown honey
mesquite by 1 day after spraying 0.28 hg ha'1
clopyralid (36). Enhanced absorption and trans-
port of clopyralid may be partially explained by
the enhanced spray retention of clopyralid on
the leaves with use of a surfactant (33, 36, 40).

Organosilicone surfactants, Silgard 309 or
Silwet L-77, added to the spray solutions at 0.1,
0.25, or 0.5 percent by volume did not increase
spray deposition, absorption, translocation, or
phytotoxicity of clopyralid in greenhouse-
grown honey mesquite (42).

Spray Characteristics

The addition of surfactant WK at 0.5 percent
(v/v) caused increased uptake of clopyralid by
the upper canopy of greenhouse grown honey
mesquite (33). Enhanced uptake after 24 hours
was probably a result of a twofold increase in
deposit of clopyralid on the plant (33, 40).
Greater deposit of clopyralid on plant surfaces
after addition of surfactant was associated with
reduced liquid surface tension and greater per-
centage of spray volume in small droplets
(<204 pm diam.). The addition of surfactant
WK at 0.5 percent (v/v) of the spray solution
caused a twofold increase in deposition of the
monoethanolamine salt of clopyralid but not
the oleylamine salt (40). There were no differ-
ences in spray deposit between spray droplet
size spectrums of 160 or 330 1.1m Dv.5 or spray
solution application of 47 or 187 l ha'1.

An air-assist spray nozzle at 9.4 l ha'1 by vol-
ume resulted in greater initial clopyralid
deposit and detection in the upper canopy of
greenhouse-grown honey mesquite than appli-
cation by conventional hydraulic nozzle at 9.4

_ or 187 1 ha"1 (42). Air-assist application did not

increase phytotoxicity compared with hydraulic
nozzles. In the field, honey mesquite mortality
and canopy reduction 16 months after aerial
application of clopyralid were significantly less
in the 624 11m droplets treatment in two of
four experiments, when compared with plots
treated with smaller droplet sizes (325 and

475 pm Dv.5) (104). Mortality increased with
larger spray volumes (19, 37, and 75 l ha'1) par-
ticularly with the 625 pm droplet size. Mortali-
ty data show that larger droplets sizes require
larger spray volumes for greatest efficacy.

pH Affects
See pH Affects under Foliar Absorption.

Temperature and
Relative Humidity

Translocation of 2,4,5-T in honey mesquite
seedlings was primarily basipetal (downward)
from the point of application at 21 C, both
acropetal (upward) and basipetal at 29 C, and
only a short distance acropetal at 38 C (88).
The quantities of 2,4,5-T translocated into
untreated tissues at 38 C were less than at 21 C
and 29 C. The highest concentrations of 2,4,5-T
were found in tissues with highest soluble
sugar concentrations. From 3 to 27 percent of
the 2,4,5-T absorbed by honey mesquite leaves
was subsequently detected in untreated stem,
leaf, and root tissues. Total amounts of C14 (car-
boxyl-labeled 2,4,5-T) detected in the untreated
tissues of the seedlings tended to increase, par-
ticularly in the roots and lower stems, with
increasing humidity.

Radosevich and Bayer (90) found that 2,4,5-
T, triclopyr, and picloram transport was greater
in periods of warm temperatures (29 C day and
13 C night) and long days (16-hour photoperi-
od) than at cool temperatures (13 C and 2 C
day and night) and a 12-hour photoperiod in
five plant species as revealed by autoradi-
ographs. They found little metabolism of any
herbicide, and each herbicide moved readily in
the symplast (phloem); however, root applica-
tion revealed limited apoplastic (xylem stream)
mobility.

l5

Rainfall

See Rainfall under Foliar Absorption.

Time of Day
See Time of Day under Foliar Absorption.

Light

Light intensity affected translocation of
2,4,5-T to the roots of woody plants (15). There
was a negative linear relationship between light
intensity and 2,4,5-T content of post oak roots.
In water oak roots, however, herbicide levels
increased as light intensity increased. In long-
leaf pine and American holly, translocation was
not significantly influenced by light intensity.
Herbicide translocation in honey mesquite as
influenced by light has not been measured.

Moisture Stress

Moderate moisture stress in beans did not
have a significant effect on the translocation of
picloram but did have on the translocation of
2,4,5-T (80). Advanced stress significantly
reduced the translocation of both herbicides.
However, translocation of 2,4,5-T was appar-
ently more sensitive to changes in moisture
stress than was translocation of picloram.
Picloram was more mobile than 2,4,5-T at all
moisture stress levels studied. After 4 hours, as
much picloram was translocated to the apex
and central stem of bean plants from a 24 pg
application as there was 2,4,5-T at 8 hours
after a 5O 11g application. This agrees with stud-
ies on honey mesquite in which both herbi-
cides were detected in the apex only 4 hours
after treatment, but only picloram occurred in
the roots (48). After 24 hours, the apex and
roots contained more picloram than 2,4,5-T.
The phloem-cortex accumulated greater quanti-
ties of picloram than the xylem-pith, indicating
major transport via the symplast. After 9O
hours, herbicide concentrations in most tissues
were unchanged or higher than after 24 hours.
These data support observations by Meyer et
al. (82) which indicated a period of 3 to 4 days
was required for honey mesquite to absorb and
translocate herbicide for maximum killing of
stems. Moisture stress sufficient to slow growth
markedly reduced transport of picloram and
2,4,5-T into untreated tissues.

Bovey et al. (24) found that 1 to 1 combina-
tion of the triethylamine salts of picloram and
2,4,5-T was more effective on huisache and

Macartney rose when applied in the evening
than in the morning or at midday in field stud-
ies. Internal water stress of the plants was less
at night after the 6:00 p.m. treatment than after
the 6:00 a.m. or 1:30 p.m. treatment, allowing
more favorable environment for absorption and
translocaion of the herbicide.

Bovey and Clouser (41) found in preliminary
studies that water stress of -1.3 to -2.8 MPa did
not affect absorption and translocation of
clopyralid in greenhouse-grown honey
mesquite 4 or 24 hours after treatment.
Addition of triclopyr (synergistic) to clopyralid
increased clopyralid uptake at low water stress
(-1.3 MPa) but decreased clopyralid uptake at
high water stress (-2.8 MPa).

Other Factors

Meyer et al. (83) sprayed honey mesquite in
the field with three herbicides at 14 different
dates during 1969 and 1970. Most effective
control of honey mesquite occurred from treat-
ments applied between April 30 and July 6.
Picloram and a picloram and 2,4,5-T (1:1) mix-
ture were the most effective herbicides. Plant
characteristics most closely associated with
control included widest translocating phloem
thickness, most rapid rate of new Xylem ring
radial growth, and lowest predawn leaf mois-
ture stress. Environmental variables most clear-
ly associated with honey mesquite control were
lower maximum air temperatures of 25 C to 36
C 1 week before treatment, maximum soil tem-
perature of 17 C to 26 C at a depth of 91 cm 1
week before treatment, and decreasing percent
soil moisture from 25 to 18 percent at a depth
of 61 to 91 cm 1 week before treatment. In
subsequent studies (84) of responses to spray-
ing on 36 dates from March to October during
a 4-year period, percentage of honey mesquite
canopy reduction was directly correlated with
total phloem thickness, rate of new Xylem ring
radial growth, and rate of upward methylene
dye movement in the xylem and was inversely
correlated with minimum leaf moisture stress.
Rate of new xylem ring radial growth and
thickness of translocating phloem appeared
most often in the equations.

l6

Root Penetration and
Translocation

Laboratory and Greenhouse
Studies

In the greenhouse, huisache and honey
mesquite can be killed by soil applied herbi-
cides and show as much or more picloram, tri-
clopyr or clopyralid content in root tissue up to
30 days after treatment as from foliar sprays
(17, 27, 28). However, in the field, huisache
and especially honey mesquite are difficult to
kill with soil-applied herbicides in heavy clay
soils (25, 86)

Baur and Bovey (4) studied changes in the
concentration of picloram in roots, stems, and
leaves of 20-day-old huisache and honey
mesquite plants exposed for different lengths of
time. Exposing roots to aqueous solutions of
picloram for 24 hours killed about 60 percent
of the treated plants. It took 10 times more her-
bicide to give the same response in honey
mesquite (10 ppm) as huisache (1 ppm). In
honey mesquite, picloram was redistributed
and eventually lost from the plant into the
rooting solution over a 5-day period, whereas
huisache, a more susceptible plant, showed no
redistribution or loss of picloram.

Mayeux and Johnson (76) found in Lind-
heimer pricklypear that picloram concentra-
tions within pads treated in the glasshouse
were greater when the herbicide was applied
to new pads (4.6 pg g1) after 30 days. More
picloram was translocated basipetally from
treated new pads to untreated old pads than in
the opposite direction, but concentrations in
untreated pads were low (< 1 11g g1). Little
picloram was absorbed by roots compared with
pads, and little was translocated into or out of
roots. These results conflict with the view that
the effectiveness of picloram for pricklypear
control is attributable to extensive root uptake
and acropetal transport. However, observations
of plants 6 months after treatment indicated
that soil applications were more effective than
foliar sprays in the glasshouse.

i;

Field Studies

As indicated earlier, control of honey mes-
quite by soil-applied herbicides has not been
highly effective in the field. However, triclopyr,
picloram, and clopyralid are highly effective
when applied to soil in pots supporting honey
mesquite under greenhouse conditions.
Possibly the extensive root system of honey
mesquite and impermeable heavy clay soils in
some areas may partially preclude effective
control under field conditions.

Herbicides such as picloram, dicamba, kar-
butilate, bromacil, tebuthiuron, and prometon
(21, 86, 95, 98) when applied as soil treatments
for honey mesquite control, have generally
been ineffective at economical rates. However,
honey mesquite was more effectively con-
trolled in the field when liquid formulations of
karbutilate and tebuthiuron were applied sub-
surface rather than on the soil surface (86).

Leaves absorbed large amounts of clopyralid
as foliar sprays on honey mesquite as indicated
by concentrations of 10 11g g'1 fresh wt or more
in basal stem phloem by 4 days after treatment
(35). Small quantities of clopyralid ( < 1 11g g4)
were detected in basal stem phloem after spray
applications of clopyralid to defoliated plants
or roots treated by soil application. When
applied to foliated plants, the 0.56 kg ha'1 of
clopyralid killed 6O percent or more plants, but
none were killed when clopyralid sprays were
applied to defoliated plants or when 2.2 kg ha'1
of clopyralid was applied to the soil.

Summary

Research work was initiated using translocat-
ed hormone-like herbicides for honey mesquite
control in the 1940s. Factors affecting the con-
trol of honey mesquite using 2,4,5-T were well
defined by the mid-1950s. Evaluating the
absorption and translocation of an herbicide in
early research was estimated by observing
plant response of leaf discoloration, defoliation,
abnormal growth, reduced growth, stem discol-
oration, plant mortality, and eventually, possi-
ble regrowth. Although observing and record-
ing plant responses to herbicides is essential
for evaluating herbicide activity and effective-
ness, it does little to quantify absorption and
translocation. Development of radiolabled her-
bicides and monitoring by gas chromatography
(GC) methods have helped quantify herbicide
uptake and transport. Research in the 1960s on

17

honey mesquite showed that radioisotopic and
GC methods gave comparable results when
extraction, cleanup, and analytical procedures
were identical. Most data reported herewith
used GC methods.

Work reported in the 1940s and 1950s indi-
cated that 2,4,5-T was more readily absorbed
and transported in honey mesquite than most
other chemicals including 2,4-D. In the 1960s
picloram was found to enter faster and accu-
mulate at higher concentrations than 2,4,5-T in
several woody species including honey
mesquite. By 1980 clopyralid was found to be
absorbed and transported in higher concentra-
tions in honey mesquite than 2,4,5-T, triclopyr,
or picloram and was also more effective.

In greenhouse-grown honey mesquite, herbi-
cides were detectable in the lower stem within
4 hours after foliar treatment and peak concen-
trations usually occurred 24 to 48 hours after
treatment, suggesting rapid absorption and
transport. Similar absorption and transport pat-
terns were found in field-grown honey
mesquite.

Not all woody species respond the same way
as honey mesquite. Spiny aster absorbed less
2,4-D and picloram than sunflower, and piclo-
ram concentration was usually less than 2,4-D
in spiny aster leaves. Although peak concentra-
tions of herbicide occurred 24 to 48 hours after
treatment in spiny aster leaves, foliar absorp-
tion is probably a limiting factor in its poor
response to herbicides.

Laboratory and field data suggest that the
ester form of 2,4,5-T and triclopyr are more
effective on honey mesquite than amine formu-
lations, but the amine forms of clopyralid and
picloram are more effective than the ester v
form. It is sometimes difficult to show differ-
ences in uptake and transport between herbi-
cide forms. The 2,4,5-T and picloram (1:1) mix-
ture was synergistic on some woody plants. In
honey mesquite, uptake and transport of piclo-
ram is increased in the presence of 2,4,5-T in
both greenhouse and field-grown plants.
Synergistic responses have also been shown
with clopyralid and triclopyr and clopyralid
and picloram mixtures. Uptake and transport
of clopyralid in honey mesquite may be
increased when mixed with equal ratios of tri-
clopyr or picloram compared with clopyralid
applied alone.

Recovery of 2,4,5-T in live oak was signifi-
cantly greater in mixture with picloram than in
tissues treated with 2,4,5-T alone. Live oak
control was best 2 years after treatment where
mixtures were used compared with either
2,4,5-T or picloram applied alone.

The effects of herbicide type, formulation,
and mixtures are discussed. The influence of

foliar spray characteristics including diluents,
adjuvants, pH, spray droplet size, and spray
volume are indicated for absorption and
translocation in woody plants as well as leaf
structure and development. Environmental fac-
tors such as air temperature, relative humidity,
rainfall, light and moisture stress are also
reviewed. "

Herbicides Discussed

Common Name

Chemical Name

Bromacil
Cacodylic acid
Clopyralid
Dicamba
2,4-D
Glyphosate
Karbutilate

MCPA
Paraquat
Picloram
Prometon
Tebuthiuron
2,4, 5-T

Triclopyr

5-bromo-6-methyl-3-( 1-methylpropyl)-2,4( 1H , Shfipyrimidinedione
dimethyl arsinic acid

3,6-dichloro-2-pyridinecarboxylic acid
3,6-dichloro-Z-methoxybenzoic acid

(2,4-dichlorophenoxy)acetic acid

N-(phosphonomethyl) glycine

tert-butylcarbamic acid ester with 3-(m-hydroxyphenyl)-1, 1- dimethylurea
(m-BB-dimethylureido) phenyl tert-butylcarbamate)

(4-chloro-2-methylphenoxy)acetic acid

1, 1 '-dimethyl-4,4’-bipyridinium ion
4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid

6-methoxy-N, N ’-bis( 1-methylethyl)- 1 ,3,5-triazine-2,4-diamine
N-[5-( 1, 1-dimethylethyl)- 1 , 3 ,4-thiadiazol-2-yl]-N,N’-dimethylurea
(2,4,5-trichlorophenoxy) acetic acid
[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid

18

W,

10.

11.

12.

Literature Cited

. Anonymous. 1968. Physiological aspects of

herbicidal action. pp. 146-163 in Principles
of Plant and Animal Pest Control. Vol. 2.
Weed Control. Nat. Acad. Sci. Publ. 1597;
Washington, D.C.

. Anonymous. 1991. A comprehensive study

of Texas watersheds and their impacts on
water quality and water quantity. Texas
State Soil & Water Conservation Board,
Temple, Texas. 208 p.

. Baur, J. R., and C. R. Swanson. 1968. Effect

of nutrient level and daylengh on growth
and susceptibility of mesquite and huisache
to 2,4,5-T and picloram. pp. 35-38 in Brush
Research in Texas. Tex. Agric. Exp. Stn.
Consol. PR-2583-2609, Texas A&M Univ.,
College Station, TX.

. Baur, J. R. and R. W. Bovey. 1969.

Distribution of root-absorbed picloram.
Weed Sci. 17:524-528.

. Baur, J. R., R. W. Bovey, and J. D. Smith.

1969. Herbicide concentrations in live oak
treated with mixtures of picloram and
2,4,5-T. Weed Sci. 17:567-570.

. Baur, R. R., and R. W. Bovey. 1970. The

uptake of picloram by potato tuber tissue.
Weed Sci. 18:22-24.

. Baur, J. R., R W. Bovey, R. D. Baker, and I.

Riley. 1971. Absorption and penetration of
picloram and 2,4,5-T into detached live oak
leaves. Weed Sci. 19:138-141.

. Baur, J. R. and J. J. Bowman. 1972. Effect

of 4-amino-3,5.6-trichloropicolinic acid on

protein synthesis. Physiol. Plant 27:354-359.
. Baur, J. R. and J. J. Bowman. 1973. Subcell-

ular distribution of picloram. Physiol Plant.
28:372-373.

Baur, J. R., R. W. Bovey, and J. D. Smith.
1972. Effect of DMSO and surfactant
combinations on tissue concentrations of
picloram. Weed Sci. 20:298-302.

Baur, J. R., R. W Bovey, and I. Riley. 1974.
Effect of pH on foliar uptake of 2,4,5-T-114
C. Weed Sci. 22:481-486.

Beck, D.L., R.E. Sosebee, and E. B.
Herndon. 1975. Control of mesquite
regrowth of different ages. J. Range
Manage. 28:408-410.

19

13.

14.

15.

16.

18.

19.

20.

21.

22.

23.

24.

25.

26.

Beck D. L., R. E. Sosebee, and E. B.
Herndon. 1975. Control of honey mesquite
by shredding and spraying. J. Range
Manage. 28:487-490.

Behrens, R. 1957. Influence of various com-
ponents on the effectiveness of 2,4,5-T
sprays. Weeds 5:183-197.

Brady, H. A. 1969. Light intensity and the
absorption and translocation of 2,4,5-T by
woody plants. Weed Sci. 17:320-322.

Bovey, R. W and F. S. Davis. 1967. Factors
affecting the phytotoxicity of paraquat.
Weed Res. 7:281-289.

. Bovey, R. W, F. S. Davis, and M. G.

Merkle. 1967 . Distribution of picloram in
huisache after foliar and soil applications.
Weeds. 15:245-249.

Bovey, R. W, F. S. Davis, and H.L. Morton.
1968. Herbicide combinations for woody
plant control. Weeds 16:332-335.

Bovey, R.W, and J. D. Diaz-Colon. 1969.
Effect of simulated rainfall on herbicide
performance. Weed Sci. 17:154-157.

Bovey, R. W., C. C. Dowler, and M. G.
Merkle. 1969. The persistence and move-
ment of picloram in Texas and Puerto Rican
soils. Pest. Morit. J. 3:177-181.

Bovey, R. W, H. L. Morton, J. R. Baur, J.
D. Diaz- Colon, C. C. Dowler, and S. K.
Lehman. 1969. Granular herbicides for
woody plant control. Weed Sci. 17:538-541.

Bovey, R. W, and C. J. Scifres. 1971.
Residual characteristics of picloram in
grassland ecosystems. Tex. Agric. Exp. Stn.
B-1111. 24p.

Bovey, R. W, J. R. Baur, and J. D. Diaz-
Colon. 1974. Phytotoxicity of 2,4,5-T, piclo-
ram and dicamba alone and in mixtures in
tissue culture. Weed Sci. 22:191-192.

Bovey, R. W, R. H. Haas, and R. E. Meyer.
1977. Daily and seasonal response of
huisache and Macartney rose to herbicides.
Weed Sci. 20:577-580.

Bovey, R. W, and R. E. Meyer. 1978.
Control of huisache with soil applied herbi-
cides. J. Range Manage 31:179-182.

Bovey, R. W, R. E. Meyer, and H. L.
Morton. 1979. Use of a woody plant nurs-
ery in herbicide research. Tex. Agric. Exp.
Stn. B-1216. 80 p.

27.

28.

Z9.

30.

31.

32.

33.

34.

35.

36.

37.

Bovey, R. W, M. L. Ketchersid, and M. G.
Merkle. 1979. Distribution of triclopyr and
picloram in huisache (Acacia farnesiana).
Weed Sci 27:527-531.

Bovey, R. W., and H. S. Mayuex, jr. 1980.
Effectiveness and distribution of 2,4,5-T,
triclopyr, picloram, and 3,6-dichloropicolin-
ic acid in honey mesquite (Prosopis juliflora
var. glandulosa). Weed Sci. 28:666-670.

Bovey, R. W., and A. L. Young 1980.
Physiological effects of phenoxy herbicides
in higher plants. pp.217-238 in The Science
of 2,4,5-T and Associated Phenoxy
Herbicides. john Wiley & Sons. New York

- NY. 462 p.

Bovey, R. W, H. Hein, jr., and R. E. Meyer.
1983. Absorption and translocation of tri-
clopyr in honey mesquite (Prosopis juliflora
var. glandulosa) Weed Sci. 31:807-812.

Bovey, R. W., H. Hein, jr., and R. E. Meyer.
1986. Concentration of 2,4,5-T, triclopyr,
picloram and clopyralid in honey mesquite
(Prosopis glandulosa) Stems. Weed Sci.
34:211-217.

Bovey, R. W., and R. E. Meyer. 1981. The
response of honey mesquite to herbicides.
Tex. Agric. Exp. Sta. B-1363. 12 p.

Bovey, R. W., H. Hein, jr., R E. Meyer, and
L. F. Bouse, 1987. Influence of adjuvants
on the depositon, absorption and transloca-
tion of clopyralid in honey mesquite
(Prosopis glandulosa) Weed Sci. 35:253-258.

Bovey, R. W, and R. E. Meyer. 1987.
Influence of adjuvants and plant growth
regulators on herbicide performance in
honey mesquite. j. Plant Growth Regul.
5:225-234.

Bovey, R. W., H. Hein, jr., and R. E. Meyer,
1988. Mode of clopyralid uptake by honey
mesquite (Prosopis glandulosa). Weed Sci.
36:269-272.

Bovey, R. W, H. Hein, jr., and R. E. Meyer.
1988. Phytotoxicity and uptake of

clopyralid in honey mesquite (Prosopis glan-

dulosa) as affected by adjuvants and other
herbicides. Weed Sci. 36:20-23.

Bovey, R. W, H. Hein, jr., and F. N.
Nelson. 1989. Phytotoxicity, absorption and
translocation of five clopyralid formula-
tions in honey mesquite (Prosopis glandu-
losa). Weed Sci. 37:19-22.

2O

39.

40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

. Bovey, R. W., H. Hein, jr., R., F. N. Nelson

and S. G. Whisenant, 1990. Phytotoxicity
and transport of clopyralid from three for-
mulations in honey mesquite. j. Plant
Growth Regul. 9:65-69.

Bovey, R. W, R. E. Meyer, and S. G.
Whisenant. 1990. Effect of simulated rain-
fall on herbicide performance in huisache
(Acacia farnesiana) and honey mesquite

(Prosopis glandulosa) Weed Technol. 4:52-55.

Bovey, R. W, R. A. Stermer and L. F.
Bouse. 1991. Spray deposit of clopyralid on
honey mesquite (Prosopis glandulosa Torr.).
Weed Technol. 5: 499-503.

Bovey, R. W, and A. R. Clouser 1998.
Unpublished data.

Bovey, R. W., E. Franz, and S. G.
Whisenant. 1994. Influence of organosili-
cone surfactants and spray nozzle types on
the fate and efficacy of clopyralid in honey
mesquite (Prosopis glandulosa) Weed Sci.
42:658-664.

Brown, j. R., and S. Archer. 1989. Woody
plant invasion of grasslands: establishment
of honey mesquite (Prosopis glandulosa var.
glandulosa) on sites differing in herbaceous
biomass and grazing history. Oecologia
80:19-26.

Crafts A. S. 1961. The Chemistry and
Mode of Action of Herbicides. Interscience
Publishers. john Wiley & Sons. N.Y. 269 p.

Crafts, A. S. 1961. Translocation in Plants.
Holt, Rinehart and Winston, Inc. N .Y. 182

p.
Crafts, A. S. 1964. Herbicide behavior in
the plant. pp. 75-110 in L. j. Audus (ed).

The Physiology and Biochemistry of
Herbicides. Academic Press. London & N.Y.

Crafts, A.S., and S. Yamaguchi. 1964. The
autoradiography of plant materials. Cali-

fornia Agric. Exp. Stn., Davis, California.
Manual 35. 143 p.

Davis, F. S., M. G. Merkle, and R. W
Bovey. 1968. Effect of moisture stress on
the absorption and transport of herbicides
in woody plants. Bot. Gaz. 129:183-189.

Davis, F. S., R. W. Bovey, and M. G.
Merkle. 1968. The role of light, concentra-
tion, and species in foliar uptake of herbi-
cides in woody plants. Forest Sci. 17:164-
169.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

Davis, F. S., R. W. Bovey, and M. G.
Merkle. 1968. Effect of paraquat and 2,4,5-
T on the uptake and transport of picloram
in woody plants. Weeds Sci. 16:336-339.

Davis, F. S., R. E. Meyer, j. R. Baur, and R.
W. Bovey. 1972. Herbicide concentrations
in honey mesquite phloem. Weed Sci.
20:264-267.

Diaz-Colon, j. D., R. W Bovey, F. S. Davis,
and j. R. Baur. 1972. Comparative effects
and concentration of picloram, 2,4,5-T and
dicamba tissue culture. Physiol Plant.
27:60-64.

Fisher, C.E., j. L. Fults, and H. Hopp.
1946. Factors affecting action of oils and
water-soluble chemicals in mesquite eradi-
cation. Ecol. Monographs 16:109-126.

Fisher, C. E., and D. W. Young. 1948.
Some factors influencing the penetration
and mobility of chemicals in the mesquite
plant. Proc. North Central Weed Control
Conf. 6:197-202.

Fisher, C. E. and D. W. Young. 1949.
Airplane application of herbicides to
mesquite (Prosopis juliflora). North Central
Weed Control Conf. Res. Rep. 6:148
(Abstract).

Fisher, C. E., and D. W Young. 1949. Tip
immersion studies on mesquite (Prosopis
juliflora). North Central Weed Control
Conf. Res. Rept. 6:214-215 (Abstract).

Fisher, C.E., C. H. Meadors, and R.
Behrens. 1956. Some factors that influence
the effectiveness of 2,4,5-trichlorophenoxy-
acetic acid in killing mesquite. Weeds
4:139-147.

Fisher, C.E., C.H. Meadors, R. Behrens, E.
D. Robinson, P.T. Marion, and H. L.
Morton. 1959. Control of mesquite on graz-
ing lands. Tex. Agric. Exp. Stn. Bull. 935.
24 p.

Fisher, C.E., H. T. Wiedemann, j. R.
Walter, C. H. Meadors, j. H. Brock, and B.
T. Cross. 1972. Brush control research on
rangeland. Tex. Agric. Exp. Stn. MP-1043.
18 p.

Hoffman, G. O. 1975. Control and manage-
ment of mesquite on rangeland. Tex. Agric.
Ext. Serv. MP-386. 15 p.

21

61.

62.

63.

64.

65.

66.

67.

68.

69.

70.

71.

72.

Hoffman, G. O. 1979. Personal communi-
cation. Tex. Agric. Ext. ServT, Texas A&M
University; College Station, TX..

Hull, H. M. 1956. Studies on herbicidal
absorption and translocation in velvet
mesquite seedlings. Weeds 4:22-42.

Hull, H. M. 1970. Leaf structure as related
to absorption of pesticides and other com-
pounds. pp. 45-93 in F. A. Gunther & j. D.
Gunther (eds.). Residue Reviews. Vol. 31.
Springer-Verlag; New York, NY.

Hull, H. M., H. L. Morton, and j. R.
Warrie. 1975. Environmental influences on
cuticle development and resultant foliar
penetration. Bot. Review 41:421-452.

jacoby, P. W, R. j. Ansley, C. H. Meadors,
and A. H. Huffman. 1990. Epicuticular wax
in honey mesquite: Seasonal accumulation
and intraspecific variation. j. Range
Manage. 43:347-350.

jacoby, R. W, R. j. Ansley, and C. H.
Meadors. 1991. Late season control of
honey mesquite with clopyralid. j. Range
Manage. 44:56-58.

Mayeux, H. S., jr., D. L. Draw and C. j.
Scifres. 1979. Control of common golden-
weed with herbicides and associated forage
release. j. Range Manage. 32:271-274.

Mayeux, H. S., jr., C. j. Scifres, and R. E.
Meyer. 1979. Some factors affecting the
response of spiny aster to herbicide sprays.
Texas Agric. Exp. Sta. B. 1197. 16 p.

Mayeux, H. S., jr., and W R. jordon. 1980.
Epicuticular wax content and herbicide
penetration of goldenweed leaves. Proc.
South. Weed Sci. 33:289. (Abstract)

Mayeux, H. S., jr., and C. j. Scifres. 1980.
Foliar uptake and transport of 2,4-D and
picloram by Drummond's goldenweed.
Weed Sci. 28:678-682.

Mayeux, H. S., jr., and W R. jordon. 1981.
Rainwash and water stress alter epicuticu-
lar wax content of goldenweed leaves.
Proc. South. Weed Sci. Soc. 34:264.
(Abstract)

Mayeux, H. S., jr., W R. jordon, R. E.
Meyer and S. M. Meola. 1981. Epicuticular
wax on goldenweed (Isocoma spp.) leaves:
variation with species and season. Weed
Sci. 29:389-393.

73.

74.

75.

76.

77.

78.

79.

80.

81.

82.

83.

84.

Mayeux, H. S., Jr., and C. J. Scifres. 1981.
Drummond's goldenweed and its control
with herbicides. J. Range Manage. 34:98-
101.

Mayeux, H. S., Jr., and W R. Jordon. 1984.
Variation in amounts of epicuticular wax
on leaves of Prospis glandulosa. Bot. Gaz.
145:26-32.

Mayeux, H. S. Jr., and W. R. Jordan. 1987.
Rainfall removes epicuticular waxes from
Isocoma leaves. Bot Gaz. 148:420-425.

Mayeux, H. S., Jr., and H. B. Johnson.
1989. Absorption and translocation of
picloram by Lindheimer pricklypear

- (Opuntia lindheimer) Weed Sci. 37:161-166.

Mayeux, H. S., Jr., and R. E. Wilkinson.
1990. Composition of epicuticular wax on
Prosopis glandulosa leaves. Bot. Gaz.

1 5 1:240-244.

McCall, H. G., C. J. Scifres, and M. G.
Merkle. 1974. Influence of foam adjuvants
on activity of selected herbicides. Weed
Sci. 22:384-388.

Merkle, M. G., and F. S. Davis. 1966. The
use of gas chromatography for determing
the translocation of picloram and 2,4,5-T.
Proc. South. Weed Conf. 19:557-561.

Merkle, M. G., and F. S. Davis. 1967. Effect
of moisture stress on absorption and move-
ment of picloram and 2,4,5-T in beans.
Weeds 15:10-13.

Meyer, R. E., H. L. Morton, R. H. Haas,
and E. D. Robison. 1971. Morphology and
anatomy of honey mesquite. USDA, ARS
and Tex. Agric. Exp. Stn. Tech. Bull. No.
1423. 186 p.

Meyer, R. E., R. W Bovey, T. E. Riley, and
W T. Mckelvy. 1972. Leaf removal effect
after sprays to woody plants. Weed Sci.
20:498-501.

Meyer, R. E., R. W. Bovey, W T. McKelvy,
and T. E. Riley. 1972. Influence of plant
growth stage and environmental factors on
the response of honey mesquite to herbi-
cides. USDA, ARS and Tex. Agric. Exp. Stn.
B-1127. 19 p.

Meyer, R. E. 1977. Seasonal response of
honey mesquite to herbicides. USDA, ARS
and Tex. Agric. Exp. Stn. B-1174. 14 p.

22

85.

86.

87.

88.

89.

90.

91.

92.

93.

94.

95.

Meyer, R. E., and S. M. Meola. 1978.
Morphological characteristics of leaves and
stems of selected Texas woody plants.
USDA, ARS Tech Bull No. 1564. 200p.

Meyer, R. E., and R. W Bovey. 1979.
Control of honey mesquite (Prosopis juliflo-
ra var. glandulosa) and Macartney rose
(Rosa bracteata) with soil-applied herbi-
cides. Weed Sci. 27:280-284.

Meyer, R. E., and R. W Bovey. 1986.
Influence of environment and stage of
growth on honey mesquite (Prosopis glandu-
losa) response to herbicides. Weed Sci.
34:287-299.

Morton, H. L. 1966. Influence of tempera-
ture and humidity on foliar absorption,
translocation, and metabolism of 2,4,5-T by
mesquite seedlings. Weeds 14:136-140.

Morton, H. L., F. S. Davis, and M. G.
Merkle. 1968. Radioisotopic and gas chro-
matographic methods for measuring
absorption and translocation of 2,4,5-T by
mesquite. Weed Sci. 16:88-91.

Radosevich, S. R., and D. E. Boyer. 1979.
Effect of temperature and photoperiod on
triclopyr, picloram, and 2,4,5-T transloca-
tions. Weed Sci. 27:22-27.

Reynolds, H. G., and F. H. Tschirley. 1957.
Mesquite control on southwestern range-
lands. USDA Leafl. No. 421. 8 p.

Robison, E. D. 1967 . Response of mesquite
to 2,4,5-T, picloram, and 2,4,5-T/picloram
combinations. Proc. South. Weed Conf.
20:199 (Abstract).

Scifres, C. J., R. W Bovey, and M. G.
Merkle. 1972. Variation in biossay attribut-
es as quantitative indices of picloram in
soils. Weed Res. 12:58-64.

Scifres, C. J., J. R. Baur, and R. W Bovey.
1973. Absorption of 2,4,5-T applied in vari-
ous carriers to honey mesquite. Weed Sci.
21:94-96.

Scifres, C. J., R. W Bovey, C. E. Fisher, and
J. R, Baur. 1973. Chemical control of
mesquite. pp. 24-32 in C. J. Scifres (ed).
Mesquite. Tex. Agric. Exp. Stn. Res.
Monograph 1.

96.

9'7.

98.

99.

100.

101.

102.

Scifres, C. ]., C. R. Kienast, and D. j.
Elrod. 1973. Honey mesquite seedling
growth and 2,4,5-T susceptibility as influ-
enced by shading. ]. Range Manage.
26:58-60.

Scifres, C. ]., H. G. McCall, and D. W.
Fryrear. 1974. Foam systems as herbicide
carriers for range improvement. Tex.
Agric. Exp. Stn. MP-1156. 19 p.

Scifres, C. ]., J. L. Mutz, and C. H.

Meadors. 1978. Response of range vegeta-
tion to grid placement and aerial applica-
tion of karbutilate. Weed Sci. 26:139-144.

Smith, H. N ., and C. A. Rechenthen.
1964. Grassland restoration. Part I. The
Texas brush problem. USDA, Soil Conserv.
Serv. Temple, TX. 4-19114. 16 p.

Swanson, C. R., and]. R. Baur. 1969.
Absorption and penetration of picloram in
potato tuber discs. Weed Sci. 97:311-314.

Tschirley, F. H., and H. M. Hull. 1959.
Susceptibility of velvet mesquite to an
amine and an ester of 2,4,5-T as related to

various biological and meteorological fac-
tors. Weed 7 1427-435.

Valentine, K. A., and]. ]. Norris. 1960.
Mesquite control with 2,4,5-T by ground
spray application. New Mexico State
Univ. Agric. Exp. Stn. Bull. 451. 24 p.

23

103.

104.

105.

106.

107.

108.

109.

Welch, T. G. 1990. Acres of Texas range-
land treated for brush and weed control.
A compilation of acreage data from 1940-
1988. Tex. Agric. Ext. Serv., College
Station, Texas. 16 p.

Whisenant, S. G., L. F. Bouse, R. A.
Crane, and R. W Bovey. 1993. Droplet
size and spray volume effects on honey
mesquite mortality with clopyralid. J.
Range Manage. 46:257-261.

Wilkinson, R. E., and H. S. Mayeux, Jr.
1987. Composition of epicuticular wax on
Isocoma leaves. Bot Gaz. 148:12-16.

Wilkinson, R. E., and H. S. Mayeux, ]r.,
1990. Composition of epicuticular wax on

Opuntia engelmanii. Bot. Gaz. 1512342-347.

Young. D. W, and C. E. Fisher 1949.
Shield tests on mesquite (Prosopis juliflo-
ra). North central weed control Conf.,
Res. Rept. 6:200 (Abstract).

Young, D. W, and C. E. Fisher. 1949.
Treatments to the foliage of mesquite

(Prosopis juliflora) with ground equipment.

North Central Weed Control Conf. Res.
Rept. 6:147 (Abstract).

Young, D. W, and C. E. Fisher. 1950.
Toxicity and translocation of herbicides in
mesquite. Proc. North Central weed
Control Conf. 7:95-99.

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