ArticlePDF Available

Abstract and Figures

Glyphosate has been widely used to control annual, perennial, and biennial weeds including Conyza species. Conyza sumatrensis (Sumatran fleabane) is considered a highly invasive and troublesome weed worldwide, including in European and Mediterranean regions. In Turkey, the use of glyphosate in orchards has recently increased; however, extensive use of glyphosate has resulted in poor control of C. sumatrensis in several peach orchards. The objectives of this research were to determine if C. sumatrensis is resistant to glyphosate and identify alternative herbicides with different modes of action that can be used instead of glyphosate. Two dose response studies were conducted in the greenhouse to evaluate the response of four C. sumatrensis populations to glyphosate, chlorsulfuron, and metribuzin. Glyphosate isopropyl amine and glyphosate potassium was applied at 0, 0.25, 0.5, 1, 2, 4, and 8 times the use rate of 1080 g a.e./ha (a.e. indicates acid equivalent) when the plants were at rosette (5–6 true leaves) and vegetative (20–22 cm tall) stages. Effects of both glyphosate formulations were combined. The resistant populations showed higher resistance 3.8 to 6.6 and 5.3 to 7.8 times at rosette stage and vegetative stage, respectively, compared with the susceptible population. Furthermore, glyphosate-resistant populations were treated with chlorsulfuron and metribuzin at 0, 0.25, 0.5, 1, 2, 4, and 8 times use rate of 7.5 and 350 g a.i./ha, respectively at the rosette stage. The glyphosate-resistant populations exhibited 2.4 to 3.8 times more resistance to chlorsulfuron, but were adequately controlled with metribuzin.
Content may be subject to copyright.
HORTSCIENCE 54(5):873–879. 2019. https://doi.org/10.21273/HORTSCI13749-18
Sumatran Fleabane (Conyza
sumatrensis) Resistance to Glyphosate
in Peach Orchards in Turkey
Deniz
_
Inci
1
Faculty of Agriculture and Natural Sciences, D
uzce University, D
uzce
81620, Turkey
Liberty Galvin and Kassim Al-Khatib
2
Plant Sciences Department, University of California, Davis, One Shields
Avenue, Davis, CA 95616
Ahmet Uluda
g
Faculty of Agriculture, Cxanakkale Onsekiz Mart University, Cxanakkale
17100, Turkey
Additional index words. glyphosate isopropyl amin, glyphosate potassium, chlorsulfuron,
metribuzin, Conyza sumatrensis (Retz.) E. H. Walker, Prunus persica Batsch, herbicide
resistance, dose response
Abstract. Glyphosate has been widely used to control annual, perennial, and biennial
weeds including Conyza species. Conyza sumatrensis (Sumatran fleabane) is considered a
highly invasive and troublesome weed worldwide, including in European and Mediter-
ranean regions. In Turkey, the use of glyphosate in orchards has recently increased;
however, extensive use of glyphosate has resulted in poor control of C. sumatrensis in
several peach orchards. The objectives of this research were to determine if C.
sumatrensis is resistant to glyphosate and identify alternative herbicides with different
modes of action that can be used instead of glyphosate. Two dose response studies were
conducted in the greenhouse to evaluate the response of four C. sumatrensis populations
to glyphosate, chlorsulfuron, and metribuzin. Glyphosate isopropyl amine and glyph-
osate potassium was applied at 0, 0.25, 0.5, 1, 2, 4, and 8 times the use rate of 1080 g a.e./ha
(a.e. indicates acid equivalent) when the plants were at rosette (5–6 true leaves) and
vegetative (20–22 cm tall) stages. Effects of both glyphosate formulations were combined.
The resistant populations showed higher resistance 3.8 to 6.6 and 5.3 to 7.8 times at
rosette stage and vegetative stage, respectively, compared with the susceptible popula-
tion. Furthermore, glyphosate-resistant populations were treated with chlorsulfuron and
metribuzin at 0, 0.25, 0.5, 1, 2, 4, and 8 times use rate of 7.5 and 350 g a.i./ha, respectively
at the rosette stage. The glyphosate-resistant populations exhibited 2.4 to 3.8 times more
resistance to chlorsulfuron, but were adequately controlled with metribuzin.
Glyphosate [N-(phosphonomethyl)-glycine]
is a systemic, nonselective, postemergence
herbicide that controls more weed species than
any other herbicide (Duke, 2018; Heap and
Duke, 2018). It has been used to control
annual, perennial, and biennial species of
grasses, sedges, and broadleaf weeds (Dinelli
et al., 2006). Glyphosate inhibits the enzyme
5-enolpyruvlshikimate-3-phosphate synthase
(EPSPS), which catalyzes the reaction of
shikimate-3-phosphate and phosphoenolpyruvate
to form 5-enolpyruvil-shikimate-3-phosphate
(Fernandez et al., 2015; Gonz
alez-Torralva
et al., 2012). Inhibition of EPSPS prevents
the biosynthesis of phenylalanine, trypto-
phan, tyrosine, and other aromatic com-
pounds in sensitive plants (Amaro-Blanco
et al., 2018; Tahmasebi et al., 2018). In
Turkey, glyphosate is the most widely used
herbicide and is registered on more than 70
crops, including peach (Torun, 2017). In the
past 5 years, the total amount of glyphosate
sold in Turkey was 1.1 million kg of acid
equivalent (Ministry of Agriculture and For-
estry, 2018).
The application of glyphosate in crop and
noncrop areas has resulted in decreased
efficacy on several populations of three
widespread species of the genus Conyza
(Amaro-Blanco et al., 2018). These species
include C. bonariensis (hairy fleabane), C.
canadensis (horseweed), and C. sumatrensis
[Sumatran fleabane (Syn. C. albida)]; there
are at least 13 hairy fleabane, 42 horseweed,
and 8 Sumatran fleabane cases of resistance
reported in field crops, orchards, forests,
pastures, urban areas, and nurseries around
the world (Heap, 2018; Mylonas et al., 2014).
Several glyphosate-resistant Conyza species
have been reported in European and Mediter-
ranean countries including France (Fernandez
et al., 2015), Spain (Amaro-Blanco et al.,
2018), Greece (Margaritopoulou et al., 2018),
and Israel (Matzrafi et al., 2015). These
species are native to the Americas (Amaro-
Blanco et al., 2018) and considered as in-
vasive and troublesome species in many parts
of the world (Matzrafi et al., 2015). They are
common weeds in orchards, row crops, road-
sides, abandoned fields, and wasteland
(Amaro-Blanco et al., 2018; Sansom et al.,
2013) and occur in more than 70 countries
(Holm et al., 1997). Currently, these Conyza
species have become established in new
territories including the Mediterranean basin
(Amaro-Blanco et al., 2018) and are invading
a variety of cropping systems (Tahmasebi
et al., 2018).
In 2015, peach growers in Cxanakkale
Province of Turkey complained about a lack
of glyphosate control of Conyza species. To
date the only report of poor Conyza species
control with glyphosate in Turkey was re-
ported in citrus orchards in Adana, Mersin,
and Hatay of Mediterranean region (Dogan
et al., 2016). No research has been conducted
to confirm and determine the level of re-
sistance in these populations.
There are 56,000 ha of cherry, apple,
pear, peach, and nectarine orchards in the
Cxanakkale Province in northwestern Tur-
key, which is considered one of the most
important fruit and vegetable production
areas in Turkey (TUIK, 2018). Currently,
C. sumatrensis is considered as the most
common troublesome weed in these or-
chards. Because of the poor control of C.
sumatrensis with glyphosate, the objectives
of this study were to confirm and identify the
level of glyphosate resistance in C. suma-
trensis and to determine the effect of chlor-
sulfuron (an acetolactate inhibitor) and
metribuzin (a photosynthetic inhibitor) on
glyphosate-resistant populations, which
some farmers use to solve the problem
despite their not being registered for use in
orchards.
Materials and Methods
Plant material. Conyza seeds were col-
lected from peach orchards where farmers
reported a lack of control with glyphosate and
from noncrop areas in the Cxanakkale Prov-
ince in northwestern Turkey. Herbicide ap-
plication records were obtained from farmers
(Table 1). Seeds were collected from three
peach orchards that had been established for
at least 10 years and from noncrop areas
where glyphosate was not used at Cxanakkale.
Before the experiments commenced, plant
species were identified by the D
uzce Univer-
sity Herbarium (Table 1). The populations
EYSAL-1, EYSAL-2, and EYYAP-3 were
selected for this study because they were
under the highest glyphosate selection pre ssure
according to growers’ records and herbicide use
history. The susceptible population, KEPKO-1
was taken from a noncrop area with no recorded
glyphosate use.
Received for publication 16 Nov. 2018. Accepted
for publication 2 Feb. 2019.
We thank the Plant Sciences Department of Uni-
versity of California, Davis for their support.
1
The first author conducted this study for an MS
thesis under the guidance of the third and fourth
authors.
2
Corresponding author. E-mail: kalkhatib@ucdavis.
edu.
HORTSCIENCE VOL. 54(5) MAY 2019 873
DISEASE AND PEST MANAGEMENT
Styrofoam seedling trays of 228 individ-
ual cells were filled with a sterilized mixture
of 1:1:2 parts by volume of white sod peat,
black peat, and white peat, then covered with
a layer of vermiculite to preserve soil mois-
ture. Each cell was seeded with 100 C.
sumatrensis seeds, and trays were placed in a
germination chamber under conditions of
25 ± 1 °C and 90 ± 3% relative humidity for
72 h. Three days after planting, the trays were
transferred to the greenhouse under the follow-
ing conditions: temperature 35/30 ± 3 °Cday/
night with 16/8-hour day/night periods; relative
humidity was 65 ± 5% during the day and 70 ±
3% during the night. Seedling emergence was
35% to 45% for all populations; once the
cotyledons reached 1 cm in height, plants were
thinned to one plant per cell and uniform plants
were selected for the dose response study.
Plants were irrigated daily to maintain adequate
soil moisture and fertilized weekly 0.8 L/m
2
with a solution containing 0.40 mg·L
–1
nitro-
gen, 0.20 mg·L
–1
phosphorus, and 0.40 mg·L
–1
potassium.
Glyphosate dose–response study. EYSAL-
1, EYSAL-2, EYYAP-3, and KEPKO-1 pop-
ulations were treated with glyphosate at the
rosette stage when plants had five or six true
leaves and at the vegetative stage when plants
were 20 to 22 cm in height. Glyphosate rates
were 0, 0.25, 0.5, 1, 2, 4, and 8 times a typical
use rate of 1,080 g a.e./ha (Table 2). Each
population was separately treated with two
formulations of glyphosate either isopropyl
amine salt or potassium salt. Treatments were
applied with a motorized backpack sprayer
(SP126; Oleo-Mac Inc., Piano, Italy), cali-
brated to deliver 250 L·ha
–1
at 166 kPa
pressure using a Lechler ST-110-02 standard
flat spray nozzle (Lechler Inc., Charles, IL).
Injury ratings were recorded at 7, 14, and 21 d
after treatment (DAT) based on a scale of 0 =
no injury and 100 = mortality. Aboveground
biomass were harvested at 21 DAT and dried
at 65 °C for 72 h and weighed.
Chlorsulfuron and metribuzin dose–response
study. EYSAL-1, EYSAL-2, EYYAP-3, and
KEPKO-1 populations were treated with chlor-
sulfuron and metribuzin to determine whether
these herbicides could be used to control
glyphosate-resistant C. sumatrensis populations.
Chlorsulfuron inhibits acetolactate synthase
(ALS), and metribuzin inhibits photosynthesis
at site A of Photosystem II (PSII). Plants were
treated at the rosette stage with 0, 0.25, 0.5, 1, 2,
4, and 8 times a typical use rate of chlorsulfuron
and metribuzin, 7.5 and 350 g a.i./ha, respec-
tively. Experiments were conducted and data
collected as described in the previous study.
Experimental Design and Data Analysis.
All dose–response experiments were repli-
cated 10 times, each experimental unit had
10 individuals, and studies were conducted
twice. Data from glyphosate isopropyl amine
and glyphosate potassium were combined
because of their insignificant difference in
variance analysis, but each application time
regarding glyphosate growing level was an-
alyzed separately. Data were analyzed using
analysis of variance and nonlinear regression
analysis to determine the herbicide rate re-
quired to cause 50% visible injury (GR
50
) and
50% dry weight reduction (GD
50
) as de-
scribed by Seefeldt et al. (1995). Dose–
response curves of the visible injury and dry
weight for different populations were plotted
as a percentage of the untreated control. GR
50
and GD
50
values were calculated, using the
following [sigmoidal logistic, three parame-
ters; SigmaPlot (ver. 11.0) software (Systat
Software Inc., San Jose, CA] equation:
y¼a
1þx
x0

b
In the model, if b>0,thenadescribes
the upper limit of y.X
0
=GR
50
or GD
50
(depending on visible injury or dry weight)
and bdescribes the slope of the curve in
GR
50
,andGD
50
(Seefeldt et al., 1995).
Resistance index (RI) levels of glyphosate-
resistance of all resistant C. sumatrensis
populations were calculated by dividing of
the GR
50
and GD
50
of the resistant popula-
tions by GR
50
and GD
50
of the susceptible
control (Matzrafi et al., 2015; Mylonas et al.,
2014). The results were considered as low
(2 #RI < 4), medium (4 #RI < 10), and high
(10 #RI) resistance levels to glyphosate
(Mei et al., 2018).
Results and Discussion
Glyphosate dose–response study. Glyph-
osate injury symptoms were apparent on all
C. sumatrensis populations, and visible in-
jury increased as glyphosate rates increased
across all treatments; however, the severity
of symptoms was more visible in the
KEPKO-1 population. Additionally, the du-
ration to develop symptoms was shorter
with KEPKO-1 population. Initial glypho-
sate injury symptoms were chlorosis and
leafcurlingfollowedbynecrosisandstunt-
ing, but injured plants showed some recov-
ery with slow growth within 14 DAT. The
recovery was more apparent in EYYAP-3,
EYSAL-1, and EYSAL-2 populations, re-
spectively, with no observed recovery in the
KEPKO-1 population. Symptoms were
more severe when plants were treated at
the rosette stage compared with the vegeta-
tive stage. C. sumatrensis visual injury and
dry weight data were similar for isopropyl
amine salt or potassium salt formulations of
glyphosate; therefore, the data were com-
bined (Figs. 1 and 2). When EYSAL-1,
EYSAL-2, and EYYAP-3 populations were
treated with glyphosate at rosette stage
(smaller plants), GR
50
rates based on visual
injury symptoms were 4401, 3046, and 5346
g a.e./ha, respectively, whereas KEPKO-1
was800ga.e./ha.WhenEYSAL-1,
EYSAL-2, and EYYAP-3 populations were
treated with glyphosate at the vegetative
stage (larger plants), GR
50
rates were
6277, 5060, and 7460 g a.e./ha, respectively,
whereas KEPKO-1 was 950 g a.e./ha
(Fig. 1). The GR
50
values for EYSAL-1,
EYSAL-2, and EYYAP-3 clearly showed
that these populations are more resistant to
glyphosate compared with KEPKO-1. The
range of glyphosate RI for EYSAL-1,
EYSAL-2, and EYYAP-3 populations was
3.8 to 6.6 (low to medium) for rosette stage
plants and 5.3 to 7.8 (medium) for vegeta-
tive stage plants (Table 3).
Table 1. Collection dates, geographical coordinates, location details, and herbicide use history for the four populations of Conyza sumatrensis used in this study.
Population Collection date Coordinate Habitat Herbicide use
z
EYSAL-1 23 Aug. 2016 40°12#02.7$N; 26°32#49.2$E Peach orchard Glyphosate >5 years
EYSAL-2 25 Aug. 2016 40°11#59.5$N; 26°32#47.4$E Peach orchard Glyphosate >5 years
EYYAP-3 5 Sept. 2016 40°11#59.3$N; 26°32#34.1$E Peach orchard Glyphosate >8 years
KEPKO-1 25 Aug. 2016 40°06#45.5$N; 26°24#14.2$E Empty area None
z
Glyphosate has been used in the orchard sites multiple times per year at over recommended doses.
Table 2. Glyphosate, chlorsulfuron, and metribuzin: main characteristics, use rate, and application period.
Herbicide Group
z
MOA
y
Rate
x
Application period
Glyphosate potassium salt 9/G EPSPS 1,323 g a.i./ha = 1,080 g a.e./ha Postemergence
Glyphosate isopropyl amin salt 9/G EPSPS 1,440 g a.i./ha = 1,080 g a.e./ha Postemergence
Chlorsulfuron 2/B ALS 7.5 g a.i./ha Postemergence
Metribuzin 5/C PSII 350 g a.i./ha Postemergence
z
Herbicide group according to Weed Science Society of America and the Herbicide Resistance Action Committee.
y
MOA: inhibitors of 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS), acetolactate synthase (ALS), and inhibitors of photosynthesis at photosystem II site
A (PSII).
x
Recommended herbicide use rate in Turkey, a.i. = active ingredient, a.e. = acid equivalent.
MOA = mode of action.
874 HORTSCIENCE VOL. 54(5) MAY 2019
The reduction in C. sumatrensis dry
weight in all populations after treatment with
glyphosate showed similar patterns to visual
injury ratings. When EYSAL-1, EYSAL-2,
and EYYAP-3were treatedwith glyphosate at
the rosette stage, GD
50
rates were 1502, 1821,
and 1570 g a.e./ha, respectively and 1099 g
a.e./ha in the KEPKO-1. When EYSAL-1,
EYSAL-2, and EYYAP-3 were treated with
glyphosate at the vegetative stage, GD
50
rates
were 4923, 5519, and 7925 g a.e./ha, re-
spectively, whereas KEPKO-1 was 1,660 g
a.e./ha (Fig. 2). The glyphosate resistance
index range was 1.36 to 1.65 (low) for the
rosette stage plants and 2.96 to 4.77 (low to
medium) for the vegetative stage plants
(Table 3).
Dose–response studies confirmed resis-
tance of C. sumatrensis to glyphosate, and
observed RI was similar to some earlier
literature that reported the RI ranging be-
tween 6.1, and 8.38 (Gonz
alez-Torralva
et al., 2012, 2014; Mei et al., 2018), but was
less than some other earlier findings that the
RI ranging 19.8 and 37.3 (Mylonas et al.,
2014; Tahmasebi et al., 2018).
Regardless of formulation and rates, glyph-
osate injury symptoms were more severe in
smaller (i.e., younger plants; rosette stage)
than in larger (i.e., older plants; vegetative
stage). The increase in glyphosate injury for
younger plants was not surprising and similar
to other previous reports (Hennigh et al.,
2005; Schuster et al., 2007; Waite et al.,
2013) because younger plants are metaboli-
cally more active, making them generally
more susceptible to glyphosate (Waite et al.,
2013). Similarly, the decrease in glyphosate
injury at larger size may be due to the
morphological and anatomical properties,
such as a thicker cuticle, characterizing more
mature plants (Waite et al., 2013; Wanamarta
Fig. 1. Percent of control by visual injury at 21 d after treatment with glyphosate applied to four Conyza sumatrensis populations at rosette and vegetative stages.
Resistance index (RI) was calculated by the ratio of the GR
50
value of the resistant population (EYSAL-1, EYSAL-2, and EYYAP-3) to the GR
50
of the
susceptible population (KEPKO-1).
HORTSCIENCE VOL. 54(5) MAY 2019 875
Table 3. Glyphosate required to cause 50% visual injury (GR
50
) and 50% dry weight reduction (GD
50
) for the four Conyza sumatrensis populations at 21 d after
treatment at two growth stages.
Population
Rosette stage Vegetative stage
GR
50
z
GD
50
z
Resistance index
y
GR
50
z
GD
50
z
Resistance index
GR50 GD50 GR50 GD50
EYSAL-1 4,401 (g a.e./ha) 1,502 5.50 1.36 6,277 (g a.e./ha) 4,923 6.60 2.96
EYSAL-2 3,046 (g a.e./ha) 1,821 3.80 1.65 5,060 (g a.e./ha) 5,519 5.32 3.32
EYYAP-3 5,346 (g a.e./ha) 1,570 6.68 1.42 7,460 (g a.e./ha) 7,925 7.85 4.77
KEPKO-1 800.0 (g a.e./ha) 1,099 1.00 1.00 950.0 (g a.e./ha) 1,660 1.00 1.00
z
GR
50
(glyphosate rate required to cause 50% visual injury) and GD
50
(glyphosate rate required to cause 50% dry weight reduction) values were calculated from
dose–response study. Glyphosate was applied at 0, 270, 540, 1080, 2160, 4320, and 8640 g a.e./ha (a.e. = acid equivalent).
y
Resistance index was calculated as the ratio of the GR
50
or GD
50
value of the resistant population to the GR
50
or GD
50
of the susceptible population (KEPKO-1).
Fig. 2. Percent of control by dry weight at 21 d after treatment with glyphosate applied to four Conyza sumatrensis populations at rosette and vegetative stages.
Resistance index (RI) was calculated by the ratio of the GD
50
value of the resistant population (EYSAL-1, EYSAL-2, EYYAP-3) to the GD
50
of the
susceptible population (KEPKO-1).
876 HORTSCIENCE VOL. 54(5) MAY 2019
and Penner, 1989). This phenomenon has
been confirmed in Conyza bonariensis and
C. canadensis, which was most likely
achieved via sequestration of the herbicide
molecule (Shaner et al., 2012). The mecha-
nisms of glyphosate resistance include re-
duced uptake and/or translocation, enhanced
detoxification of the glyphosate molecule,
expression of an insensitive form of EPSPS,
amplification of the EPSPS gene, or two
codon changes in EPSPS (Dill, 2005; Sam-
mons et al., 2018; Shaner, 2014).
Chlorsulfuron and metribuzin dose–
response study. Overall, chlorsulfuron visual
injury increased as rates increased; injury
symptoms were apparent on all populations,
but the severity of symptoms was greater on
KEPKO-1, the susceptible population. Chlor-
sulfuron symptoms were chlorosis and leaf
malformation followed by necrosis. When
EYSAL-1, EYSAL-2, and EYYAP-3 popula-
tions were treated with chlorsulfuron at the
rosette stage, GR
50
rates were 11.9, 9.1, and
14.1 g a.i./ha, respectively, whereas KEPKO-1
was 3.7 g a.i./ha (Fig. 3). The GR
50
values for
EYSAL-1, EYSAL-2, and EYYAP-3 illus-
trated that these populations are more resistant
to chlorsulfuron compared with the susceptible
KEPKO-1 population. The range of chlorsul-
furon resistance index (RI) for EYSAL-1,
EYSAL-2, and EYYAP-3 populations was
2.4 to 3.8 for rosette stage plants (Table 4).
The reduction in C. sumatrensis dry
weight for all populations after treatment
with chlorsulfuron showed response patterns
similar to visual injury ratings. When
EYSAL-1, EYSAL-2, and EYYAP-3 at the
rosette stage were treated with chlorsulfuron,
GD
50
rates were 112.5, 93.3, and 23.8 g a.i./
ha, respectively, and 8.8 g a.i./ha in the
KEPKO-1 (Fig. 3). The chlorsulfuron resis-
tance index range was 2.6 to 12.7 for rosette
stage plants (Table 4). RI, based on dry
weight reduction (GD
50
), clearly showed that
the glyphosate-resistant populations were not
effectively controlled by chlorsulfuron at
tested rates; however, visual symptoms by
chlorsulfuron application were more severe
than glyphosate symptoms. Injured plants did
not show same recovery as glyphosate-treated
plants did. In similar studies conducted with
Table 4. Chlorsulfuron required to cause 50% visual injury (GR
50
) and 50% dry weight reduction (GD
50
) for the four Conyza sumatrensis populations at 21 DAT
at rosette stage.
Population
Chlorsulfuron
GR
50
z
GD
50
z
Resistance index
y
GR
50
GD
50
EYSAL-1 11.86 (g a.i./ha) 112.5 3.20 12.7
EYSAL-2 9.088 (g a.i./ha) 93.35 2.45 10.5
EYYAP-3 14.13 (g a.i./ha) 23.77 3.81 2.69
KEPKO-1 3.706 (g a.i./ha) 8.820 1.00 1.00
z
GR
50
(herbicide rate required to cause 50% visual injury) and GD
50
(herbicide rate required to cause 50% dry weight reduction) values were calculated from
dose–response study. Chlorsulfuron was applied at 0, 1.875, 3.75, 7.5, 15, 30, and 60 g a.i./ha. KEPKO-1 was the most susceptible population in the dose–response
studies.
y
Resistance index was calculated as the ratio of the GR
50
or GD
50
value of the resistant population to the GR
50
or GD
50
of the susceptible population.
Fig. 3. Percent of control by injury at 21 d after treatment with chlorsulfuron applied to four Conyza sumatrensis populations at rosette stage. Resistance index (RI)
was calculated by the ratio of the GR
50
or GD
50
value of the resistant population (EYSAL-1, EYSAL-2, EYYAP-3) to the GR
50
or GD
50
of the susceptible
population (KEPKO-1).
HORTSCIENCE VOL. 54(5) MAY 2019 877
ALS inhibitors, C. canadensis populations
were resistant to cloransulam, chlorimuron,
imazethapyr, and bispyribac with the ranging
70, 40, 9.1, and 580, respectively (Zheng et al.,
2011). In addition, C. sumatrensis populations
are resistant to imazapyr, imazethapyr, and
amidosulfuron with the ranging 4, 3.7, and 2,
respectively, but not to chlorsulfuron (RI =
1.2) (Osuna and Prado, 2003).
Metribuzin visual injury increased as
rates increased, and injury symptoms were
apparent in all populations. Symptoms were
chlorosis and leaf distortion followed by
necrosis and full plant desiccation; visual
injury from metribuzin developed rapidly
within 1 to 7 DAT depending on the rate.
Plants showed no recovery at observations.
When EYSAL-1, EYSAL-2, and EYYAP-3
populations were treated with metribuzin
at rosette stage, GR
50
rates were 9.5, 12.3,
and 10.3 g a.i./ha, respectively, whereas
KEPKO-1 was 5.5 g a.i./ha (Fig. 4). These
rates represent 2.7%, 3.5%, 2.9%, and 1.5%
of the use rate; the GR
50
values for all
populations showed that these populations
are not resistant to metribuzin.
The reduction in C. sumatrensis dry
weight in all populations after treatment
with metribuzin was similar to visible injury
ratings. When EYSAL-1, EYSAL-2, EYYAP-3,
andKEPKO-1attherosettestagewere
treated with metribuzin, GD
50
rates were
0.042, 0.011, 0.161, and 0.033 g a.i./ha,
respectively (Fig. 4). Regardless of the
population or application rate, metribuzin
provided > 99% control on rosette stage C.
sumatrensis plants.
Conclusions
Our findings demonstrate that C. suma-
trensis populations collected from several
peach orchards from the Cxanakkale prov-
ince of Turkey are resistant to glyphosate.
The study also shows that younger plants
were more sensitive to glyphosate than
older plants. With this in mind, chemical
management practices should focus on
early stages of C. sumatrensis when glyph-
osate is the only option. Results illustrate
that C. sumatrensis populations in north-
western Turkey have resistance to glyph-
osate and chlorsulfuron but are still
susceptible to metribuzin. Consequently,
metribuzin, which has a photosynthetic
inhibitor mode of action, can be effectively
used as an alternative herbicide to control
glyphosate-resistant Conyza sumatrensis in
peach orchards but needs to be registered
and tested for fruit quantity and quality.
Literature Cited
Amaro-Blanco, I., P.T. Fern
andez-Moreno, M.D.
Osuna-Ruiz, F. Bastida, and R.D. Prado. 2018.
Mechanisms of glyphosate resistance and re-
sponse to alternative herbicide-based manage-
ment in populations of the three Conyza species
introduced in southern Spain. Pest Mgt. Sci.
74:1925–1937.
Dill, G.M. 2005. Glyphosate-resistant crops: His-
tory, status and future. Pest Mgt. Sci. 61:219–
224.
Dinelli, G., I. Marotti, A. Bonetti, M. Minelli, P.
Catizone, and J. Barnes. 2006. Physiological
and molecular insight on the mechanisms of
resistance to glyphosate in Conyza canadensis
(L.) Cronq. biotypes. Pestic. Biochem. Physiol.
86:30–41.
Dogan, M.N., K.A. Emine, T. Suleyman, and
A.T. Serim. 2016. Determination of glypho-
sate resistance of horseweed species (Conyza
spp.) occuring in citrus and vineyards from
Mediterranean and Aegean regions. Proc. of
Turkey 6th Plant Protection Congr. with Intl.
Part. p 836.
Duke, S.O. 2018. The history and current status of
glyphosate. Pest Manag. Sci. 74:1027–1034.
Fernandez, P., C. Gauvrit, F. Barro, J. Menendez,
and R.D. Prado. 2015. First case of glyphosate
resistance in France. Agron. Sustain. Dev.
35:1469–1476.
Gonz
alez-Torralva, F., A.M. Rojano-Delgado,
M.D. Luque de Castro, N. M
ulleder, and R.D.
Prado. 2012. Two non-target mechanisms are
involved in glyphosate-resistant horseweed
(Conyza canadensis L. Cronq.) biotypes. J.
Plant Physiol. 169:1673–1679.
Gonz
alez-Torralva, F., J. Gil-Humanes, F.
Barro, J.A. Domínguez-Valenzuela, and
R.D. Prado. 2014. First evidence for a tar-
get site mutation in the EPSPS2 gene in
glyphosate-resistant Sumatran fleabane
from citrus orchards. Agron. Sustain. Dev.
34:553–560.
Heap, I. and S.O. Duke. 2018. Overview of
glyphosate-resistant weeds worldwide. Pest
Manag. Sci. 74:1040–1049.
Heap, I. 2018. The International Survey of Herbi-
cide Resistant Weeds. 5 Oct. 2018. <http://
www.weedscience.org/Summary/Species.aspx>.
Hennigh, D.S., K. Al-Khatib, P.W. Stahlman, and
D.E. Shoup. 2005. Prairie cupgrass (Eriochloa
contract) and windmillgrass (Chloris verticil-
lata) response to glyphosate and acetyl-CoA
carboxylase-inhibiting herbicides. Weed Sci.
51:110–117.
Holm, L.G., J. Doll, E. Holm, J.V. Pancho, and J.P.
Herberger. 1997. World weeds: Natural histo-
ries and distribution. Wiley, NY.
Margaritopoulou, T., E. Tani, D. Chachalis, and
I. Travlos. 2018. Involvement of epigenetic
mechanisms in herbicide resistance: The
case of Conyza canadensis. Agr. 8(1):17.
Matzrafi, M., T.W. Lazar, M. Sibony, and B.
Rubin. 2015. Conyza species: Distribution
and evolution of multiple target-site herbicide
resistances. Planta 242:259–267.
Mei, Y., Y. Xu, S. Wang, L. Qiu, and M. Zheng.
2018. Investigation of glyphosate resistance
levels and target-site based resistance (TSR)
mechanisms in Conyza canadensis (L.) from
apple orchards around areas of Bohai seas and
Loess Plateau in China. Pestic. Biochem. Phys-
iol. 146:7–12.
Ministry of Agriculture and Forestry. 2018.
Republic of Turkey Ministry of Agriculture
and Forestry. 18 Oct. 2018. <https://arastirma.
tarimorman.gov.tr/zmmae/Belgeler/Sol%20Menu/
Yayınlar/
Ulkemizde%20Zirai%20M
ucadele%
20Girdilerinin%20De
gerlendirilmesi.pdf>.
Mylonas, P.N., C.N. Giannopolitis, P.G. Efthimiadis,
G.C. Menexes, P.B. Madesis, and I.G. Elefther-
ohorinos. 2014. Glyphosate resistance of mo-
lecularly identified Conyza albida and Conyza
bonariensis populations. Crop Prot. 65:207–
215.
Osuna, M.D. and R.D. Prado. 2003. Conyza albida:
A new biotype with ALS inhibitor resistance.
Weed Res. 43:221–226.
Fig. 4. Percent of control by injury at 21 d after treatment with metribuzin applied to four Conyza sumatrensis populations at rosette stage. Plants showed no
resistance, thus no RI was calculated for metribuzin.
878 HORTSCIENCE VOL. 54(5) MAY 2019
Sammons, R.D., S.O. Duke, and S.B. Powles.
2018. Glyphosate—how it became a once in a
hundred year herbicide and its future. Outlooks
Pest Mgt. 29:6.
Sansom, M., A.A. Saborido, and M. Dubois. 2013.
Control of Conyza spp. with glyphosate—a
review of the situation in Europe. Plant Prot.
Sci. 49(1):44–53.
Schuster, C.L., D.E. Shoup, and K. Al-Khatib.
2007. Response of Common Lambsquarters
(Chenopodium album) to glyphosate as af-
fected by growth stage. Weed Sci. 55:147–151.
Seefeldt, S.S., J.E. Jensen, and E.P. Fuerst. 1995.
Log-logistic analysis of herbicide dose-response
relationships. Weed Technol. 9:218–227.
Shaner, D.L., R.B. Lindenmeyer, and M.H. Ostlie.
2012. What have the mechanisms of resistance
to glyphosate taught us? Pest Mgt. Sci. 68:3–9.
Shaner, D.L. 2014. Herbicide handbook. 10th ed.
Weed Science Society of America, Champaign,
IL.
Tahmasebi, B.K., M.T. Alebrahim, R.A. Rold
an-
G
omez, H.M.D. Silveira, L.B.D. Carvalho,
R.A.D.L. Cruz, and R.D. Prado. 2018. Effec-
tiveness of alternative herbicides on three
Conyza species from Europe with and without
glyphosate resistance. Crop Prot. 112:350–355.
Torun, H. 2017. Current status of herbicides and
licensed herbicides in Turkey. Turkish J. of
Weed Sci. 20(2):61–68.
TUIK. 2018. Turkish Statistical Institute. 16 Sept.
2018. <http://www.turkstat.gov.tr/PreTablo.do?
alt_id=1001>.
Waite, J., C.R. Thompson, D.E. Peterson, R.S.
Currie, B.L.S. Olson, P.W. Stahlman, and K.
Al-Khatib. 2013. Differential kochia (Kochia
scoparia) populations response to glyphosate.
Weed Sci. 61:193–200.
Wanamarta, G. and D. Penner. 1989. Foliar absorp-
tion of herbicides. Rev. of Weed Sci. 4:215–231.
Zheng, D., G.R. Kruger, S. Singh, V.M. Davis, P.J.
Tranel, S.C. Weller, and W.G. Johnson. 2011.
Cross-resistance of horseweed (Conyza cana-
densis) populations with three different ALS
mutations. Pest Mgt. Sci. 67:1486–1492.
HORTSCIENCE VOL. 54(5) MAY 2019 879
... kat, vejetatif dönemde uygulandığında ise 5.3-7.8 dayanıklı olduğu olduğunu belirlemişlerdir [13]. Araştırmacılar dayanıklı popülasyonların chlorsulfuron'ada 2.4-3.8 ...
Article
Isparta is one of the most important apples producing areas of Turkey. Disease, pests, and weeds that result in problems in apple orchards may restrict apple production. Although the direct impact of the weeds on apples is limited, they can be significant, especially at an early stage due to competition for water, nutrients, and light. The most preferable method to prevent crop losses is herbicide use. If the herbicides were used in the same place without a rotation, herbicide resistant populations may become apparent. Implementation of resistance management following herbicide-resistant population covers more long-term and extensive studies. This study was conducted to determine Glyphosate resistance horseweed (Conyza canadensis) population in apple orchards of Isparta from 2015 to 2019. Bioassay techniques were employed to determine the resistance. In the screen test, the recommended rate of glyphosate was applied to the horseweed populations that were grown in the growth chamber and their resistances were determined. In the dose-response experiments, logarithmic rates of glyphosate were applied to horseweed populations and the impact was identified by non-linear regression analysis. I50 values of suspected glyphosate resistant populations were 96.087 and 83.126ml commercial ingredient/da and 106.48 and 98.82ml commercial ingredient/da for F1 and F2 populations, respectively. The populations separated as suspected glyphosate resistant horseweed have been considered as high-level herbicide tolerant.
... In the European Union, glyphosate has been approved until 2022, and reevaluation procedures are ongoing 8 . While glyphosate was 300 tons in Turkey in 2001, it is estimated to reach 8,000 tons in 2019 [9][10][11][12] . ...
Article
Full-text available
Purpose: The aim of this study was to investigate in vitro effect of glyphosate on Glucose 6-phosphate dehydrogenase (G6PD) enzyme activity. Materials and Methods: In terms of G6PD enzyme deficiency, samples taken from healthy and enzyme deficient male individuals were studied. After the hemolysates were prepared from blood sample, G6PD enyzme activities were determined by the modified Beutler method. Then, the effects of different concentrations (5.3x10-3, 5.3x10-4, 5.3x10-5, 5.3x10-6 mmol/mL) of glyphosate on G6PD activity were evaluated in normal and mutant enzymes. In addition, the in vitro effect of the antioxidant N-acetylcysteine (NAC) on the enzyme was investigated in the presence of glyphosate and without glyphosate. Results: While the result of normal erythrocyte G6PD activity was 12U/g for the individual, the result for the individual with enzyme deficiency was 2.5U/g Hb. The glyphosate’s maximum activity loss in the G6PD enzyme was observed in the 60th minute incubation. The highest inhibition was observed at 5.3x10-3 mmol/mL glyphosate. 4.7x10-7 mmol/mL N-Acetylcysteine partially increased the inhibition of glyphosate in the G6PD enzyme in healthy individuals, but had no effect on mutant G6PD. Conclusion: In humans, it is predicted that glyphosate affects G6PD enzyme activity in vitro and is an interference agent in the experimental process. In case of contamination, studies on limits of glyphosate that will not cause harmful effects in humans should be continued.
... The proper use of adjuvants is imperative in cases of glyphosate applications, since they reduce the surface tension of the spray liquid and may improve the efficacy of the treatments [32]. Sumatran fleabane has been reported to be more sensitive to glyphosate in earlier rather than more advanced growth stages, due to altered morphological characteristics of the leaf tissues and subsequently lower deposition of the herbicide [13,31,32]. The dose-response assays in the present study revealed that the susceptibility of C. sumatrensis to herbicidal treatments at the rosette stage (BBCH 16-18) varied among populations and depended on the glyphosate formulation and the addition of adjuvants. ...
Article
Full-text available
In this work, we studied the effect of three glyphosate formulations (isopropylamine, ammonium and potassium salts) and two non-ionic adjuvants on the resistance response of two resistant (R1, R2) and one susceptible population of the highly invasive Asteraceae, Conyza sumatrensis, from Southern France vineyards. Only in R1, an amino acid substitution (Pro106Thr) was found in the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). The two adjuvants, in a similar fashion, significantly reduced GR50 values for every population and glyphosate formulation. Without adjuvants, glyphosate as potassium salt was the only formulation able to significantly reduce the GR50 values of every population. For every population, the two adjuvants improved, indistinguishably, leaf retention of the herbicidal solution and the potassium salt formulation led to the highest retention, both with and without the adjuvant added. Uptake responses paralleled those of retention and adjuvant addition was more effective in increasing foliar uptake of the lower performing formulations (isopropylamine and ammonium salts). The allocation pattern of glyphosate among plant compartments was only dependent on population, with R2 retaining most glyphosate in the treated leaf, clearly suggesting the occurrence of a Non-Target Site Resistance (NTSR) mechanism. Results indicate that control of weed populations possessing NTSR mechanisms of resistance to glyphosate may be improved through adequate selection of formulation and adjuvant use.
Article
Full-text available
Tall fleabane is emerging as a problematic weed species in the eastern cropping region of Australia. Recently, growers indicated poor control of tall fleabane in fallow fields to the field rate of glyphosate. Pot studies were conducted in an open field at the Gatton farm of the University of Queensland, Queensland, Australia, to confirm the level of glyphosate resistance in a putative glyphosate-resistant (GR) tall fleabane population and to evaluate the performance of alternative postemergence (POST) herbicides to control GR tall fleabane. Compared with a glyphosate-susceptible (GS) population, the level of resistance in the GR population was 4- and 3.5-fold based on plant survival and biomass, respectively. The target-site resistance mechanism was not present as both the GR and GS populations had the same gene sequence. There were several effective alternative herbicides for the control of small (4-leaf stage) plants of tall fleabane, but to control large (12-14 leaf stage) plants, the sole application of saflufenacil + trifludimoxazin or its mixtures with glyphosate, glufosinate, or paraquat were the best herbicide treatments. This is the first published report on the occurrence of GR tall fleabane in Australia. Growers need to use integrated management strategies to mitigate the further spread of GR tall fleabane in fallow fields as well as glyphosate-resistant crops.
Article
Full-text available
Conyza spp. are among the most problematic broadleaf weeds in citrus orchards and grape fields in Turkey. Glyphosate is used to control weeds, but Conyza spp. can escape the treatment and grow as a monoculture in these fields. To investigate whether glyphosate-resistant biotypes of Conyza spp. exist in Turkey, seeds of Conyza spp. were collected from 131 citrus fields and 121 vineyards with heavy Conyza infestations in the Mediterranean and Aegean regions of the country. Seeds were classified by species, and initial susceptibility screenings were conducted by applying glyphosate potassium salt at 1.323 kg a.i. ha⁻¹ to seedlings at the five- to six-leaf stage. Forty-five biotypes showed less than 80% susceptibility in the screenings and were subsequently used in dose–response experiments. Assays were also conducted to measure shikimic acid accumulation in resistant and susceptible biotypes after glyphosate treatment, and molecular studies were undertaken to investigate the mechanism of resistance. Among 252 populations collected from fields, 32 biotypes showed resistance to glyphosate. Molecular studies showed that target site mechanisms including mutations or expression of the EPSPS gene did not contribute to the mechanism of glyphosate resistance in Conyza biotypes from Turkey.
Conference Paper
Full-text available
Olive has been considered a divine tree in the Mediterranean region since ancient times. The tree is vulnerable to weed presence on the early growth stage, and they cause many adverse impacts on the olive tree, including wildfire, but it was ignored by growers during the youth infertility in many times. Edremit district provides the most suitable growing conditions to olive tree; therefore, with 11 million olive trees the district is a prominent location in Turkey. This study was conducted to determine the attitude of olive growers to the weeds in the Edremit district of the Balıkesir Province, Turkey. For this aim, a questionnaire form consisted of 29 questions was prepared and applied to 20 olive orchard growers in Edremit. The results showed that age of producers were 30 to 73. Interestingly, one-third of the growers was the only considered themselves farmers, and most farmers (%65) had less than 2 ha olive orchards. The weeds were Cynodon dactylon, Sorghum halepense, Tifolium pratense, Xanthium spinosum, Tribulus terrestris, Cyperus rotundus. The growers mainly controlled them with ploughing, cutting, and herbicides. One-quarter of them only used glyphosate in the spring months to control weeds, but most of these growers applied the herbicide using knapsack sprayer. Even if the growers have general information about the loss of herbicide efficacy, half of them had any info or no action if loss of herbicide efficacy occurred. There was no relationship between age, experience, occupation, education, and size of field and methods applied for olive cultivation. It was concluded that research, training and outreach activities are necessary to increase yield and quality of olive and olive oil.
Chapter
Full-text available
Amaçlar (i) İstilacı yabancı bitkiler konusunda temel kavramlar ve bu bitkilerin etkileri (Ör.; insan sağlığı, ekonomik kayıp vb.) konularında Türkiye’de sınırlı olan Türkçe kaynaklara bir katkı sunarak ilgili konuda çalışan, eğitim alan veya ilgilenen tüm paydaşların yararlanabileceği bir kaynak oluşturmak, (ii) İstilacı yabancı bitkilerin yayılımında antropojenik faktörler konusunda farkındalıkları arttırmak, (iii) İstilacı yabancı bitkilerin yönetimine yönelik ulusal çapta alınabilecek tedbirlerin ve kontrol müdahalelerinin planlanmasına katkı sağlamaktır. Kapsam (i) İstila kapsamındaki kavramların kullanımı konusunda öneriler, ilgili konuda rehberlik eden bazı literatürlerden (Ör.; Richardson ve ark., 2000, Pyšek ve ark., 2004) faydalanılarak sunulmuştur. (ii) yabancı bitki türlerinin yeni alanlara tanıtımı / giriş yolları ve bitki istilaları ile ilgili mekanizmalar konusu tartışılmıştır. (iii) Yabancı bitki taksonlarından kaynaklanabilecek etkiler çevresel ve sosyo-ekonomik boyutları ile ele alınmış ve istilacı yabancı bitkiler ile bu bitkilerin etkilerini önlemeye yönelik alınabilecek önlemler konusunda bazı temel öneriler paylaşılmıştır. Purposes (i) To create a resource that can be used by all stakeholders who work, receive training or are interested in the subject by contributing to the limited Turkish resources in Turkey on the basic concepts of invasive alien plants and their impacts (e.g. human health, economic loss, etc.). (ii) To raise awareness of anthropogenic factors in the spread of invasive alien plants. (iii) To contribute to the planning of national measures and control interventions for the management of invasive alien plants. Scope (i) Suggestions on the use of concepts within the scope of invasion were presented by making use of some guiding literature (e.g. Richardson et al., 2000, Pyšek et al., 2004). (ii) The introduction of alien plant species into new areas/entry routes and mechanisms for plant invasion was discussed. (iii) The impacts that may arise from alien plant taxa were discussed with their environmental and socio-economic dimensions, and some basic recommendations were shared about invasive alien plants and the measures that can be taken to prevent the impacts of these plants.
Article
Full-text available
Glyphosate is the most important herbicide globally, and horseweed (Conyza canadensis) has been one of the most commonly encountered weed species that has developed resistance to it in various parts of the world, including Greece. After glyphosate application, horseweed populations show a wide range of phenotypic plasticity in response to selection pressure. In previous work, we have proposed a herbicide resistance mechanism that is not due to a point mutation at the codon 106 of EPSP synthase but most likely due to a synchronized overexpression of EPSPS and the ABC transporter genes. In the current study, it is hypothesized that the observed phenotypic alterations and differential expression of the EPSPS gene could be attributed to epigenetic changes. DNA methylation plays a pivotal role in many biological procedures such as gene expression, differentiation, and cellular proliferation. Sodium bisulfite sequencing was used to detect epigenetic changes that occur at the C5 position of cytosine residues within CpGdi nucleotides in two horseweed populations (resistant vs. susceptible). Results show differential methylation pattern between the two populations. This work will elucidate the naturally increased resistance of C. Canadensis to glyphosate and set the bases for future development of techniques that restrict weed resistance to herbicides.
Article
Full-text available
ÖZET Kimyasal mücadele dünyada yabancı otlarla mücadelede en çok tercih edilen yöntemdir. Kimyasal mücadelenin kolay uygulanması, etkisinin kısa sürede görülmesi ve ekonomik olması herbisitleri ön plana çıkarmıştır. Herbisitler farklı şekilde sınıflandırılabilmelerine rağmen, dünyada olduğu gibi Türkiye'de de etki mekanizmalarına göre sınıflandırılma tercih edilmektedir. Bu derlemede HRAC (Herbicide Resistance Action Committee) sınıflandırma sistemi ile Türkiye'de 2016 yılında ruhsatlı olan aktif maddeli ruhsatlı herbisitlerin etki mekanizması sayısı, kimyasal sınıf sayısı ve aktif madde sayıları karşılaştırılmıştır. Türkiye'de 2016 yılında 98 farklı aktif madde saptanmış, bunun yanında 45 kimyasal sınıf altında 12 farklı etki mekanizması olduğu belirlenmiştir. Türkiye'de ruhsatlı herbisitler içerisinde ilk üç sırada HRAC çerçevesinde A, B ve C gruplarına ait etki mekanizlarının sırasıyla %16, %27 ve %15 oranlarında olduğu görülmüştür. 2016 yılına göre kültür bitkisi gruplarına bakıldığında tahıllar ve endüstri bitkilerinde ruhsatlı herbisitlerin mevcut herbisitlerin %57'sini oluşturduğu, yabancı otların mücadelesinde en çok ruhsatlandırılan aktif maddenin %7,2 ile glyphosate isopropylamin tuzu ve türevlerinin (bağ, fındık, meyve bahçeleri, turunçgiller, kültür bitkisi yetiştirilmeyen alanlar) olduğu saptanmıştır. ABSTRACT The most preferred control method to manage weeds in the world is use of chemicals. Herbicides are the foreground for chemical control as they are feasible and economical. Some chemical classes and active ingredients of herbicides are classified according to their action mechanisms in Turkey as done in the world. HRAC (Herbicide Resistance Action Committee) classification system and licensed active ingredients in Turkey compared for number of licensed active ingredients, chemical classes and action mechanisms in 2016. In 2016, 98 different active substances were identified in Turkey and it was determined that there were 12 different action mechanisms under 45 chemical classes. It was seen that the action mechanisms belonging to groups A, B and C in first three ranks of licensed herbicides in Turkey are 16%, 27% and 15%, respectively. When the crop groups compared to 2016, grains and industrial plants in which form the sum of 57% of licensed herbicides to control weeds, also most licensed plant protection product of active ingredient permits against glyphosate isopropylamine salt and derivatized glyphosate with percentage of 7.2% (used in grapes, nuts, fruit orchards, citrus, non-cultivated areas).
Article
Full-text available
Glyphosate is the only herbicide to target the enzyme 5-enolpyruvyl-3-shikimate phosphate synthase (EPSPS). It is a high use rate, non-selective herbicide that translocates primarily to metabolic sinks, killing meristematic tissues away from the application site. Its phloem-mobile properties and slow action in killing weeds allows the herbicide to move throughout the plant to kill all meristems, making it effective for perennial weed control. Since commercialization in 1974, its use has grown to dominate the herbicide market. Much of its use is on transgenic, glyphosate-resistant crops (GRCs), which have been the dominant transgenic crops worldwide. GRCs with glyphosate provided the most effective and inexpensive weed management technology in history for a decade or more. However, due to the rapid increase in GR weeds, the effectiveness of glyphosate use in GRCs is declining. Critics have claimed that glyphosate-treated GRCs have altered mineral nutrition and increased susceptibility to plant pathogens because of glyphosate's ability to chelate divalent metal cations, but the complete resistance of GRCs to glyphosate indicates that chelating metal cations does not contribute to the herbicidal activity or significantly affect mineral nutrition. The rates of increases in yields of maize, soybean, and cotton in the USA have been unchanged after high adoption rates of GRCs. Glyphosate is toxic to some plant pathogens, and thereby can act as a fungicide in GR crops. Ultra-low doses of glyphosate stimulate plant growth in glyphosate-susceptible plants by unknown mechanisms. Despite rapid and widespread increases in GR weeds, glyphosate use has not decreased. However, as GR weeds increase, adoption of alternative technologies will eventually lead to decreased use.
Article
Full-text available
In Europe, glyphosate resistant populations have developed in some weed species in perennial crops, including three species of the genus Conyza documented by the International Survey of Herbicide Resistant Weeds. Conyza spp. biology is reviewed in this paper and related to population dynamics and the development of resistant populations. Suboptimal growth stage at application, improper agricultural practices such as overreliance on glyphosate and long-term use of sublethal doses are identified as the most important factors of resistance development. Current control methods in perennial crops including mixtures of glyphosate with other active ingredients are discussed and effective weed management strategies are described to manage the development and spread of glyphosate resistant Conyza spp. in Europe.
Article
Glyphosate has been applied in European countries for over a decade between rows in olive groves and grape vineyards to control Conyza species [hairy fleabane (C. bonariensis), horseweed (C. canadensis) and Sumatran fleabane (C. sumatrensis)], however poor control has been observed in recent years. Glyphosate susceptible (GS) or resistant (GR) populations were assayed in each species. In addition, Conyza spp. control with alternative herbicides (alone or in mixture with glyphosate) over two years was also assessed. The GS populations of the three species were controlled with glyphosate field doses (1080 g ae ha −1). The GR hairy fleabane, horseweed and Sumatran fleabane populations were 15.0, 15.7 and 19.8 times more resistant, respectively, than their respective GS population. The shikimic accumulation of GS populations was 4-6 times higher compared with the GR Conyza populations, confirming the glyphosate resistance of the latter ones. The increase in the glyphosate dose did not control the GR Conyza populations, despite providing a higher dry growth reduction. Glufosinate and flazasulfuron, alone or mixed with glyphosate, were the effective options to control GR and GS populations of hairy fleabane and Sumatran fleabane. However, the GR horseweed population might have evolved multiple resistance to glyphosate and flazasulfuron in Hungary. The other herbicides (PSI, auxinic and PPO) showed an additive effect together with the control provided by glyphosate in the GS and GR populations; however generally , these herbicides could be applied alone at the rosette stage. Effective herbicides with modes of action different from glyphosate, except flazasulfuron for controlling horseweed, should be used to delay the selection of herbicide resistance in perennial crops in Europe.
Article
Background: In perennial crops, the most common method of weed control is to spray herbicides, and glyphosate has long been the first choice of farmers. Three species of the genus Conyza are among the most problematic weeds for farmers, exhibiting resistance to glyphosate. The objectives of this work were to evaluate resistance levels and mechanisms, and to test chemical control alternatives in putative resistant (R) populations of Conyza bonariensis, Conyza canadensis and Conyza sumatrensis. Results: Plants of the three R-populations of Conyza spp. survived high doses of glyphosate compared to plants of susceptible (S) populations. The rate of movement of14C glyphosate out of treated leaves in plants of S-populations was higher than in plants of R-populations. Only in plants of the R-population of C. sumatrensis contained the known target-site 5-enolpyruvylshikimate-3-phosphate synthase mutation Pro-106-Thr. Field responses to the different alternative herbicide treatments tested indicated injury and high effectiveness in most cases. Conclusions: The results indicate that non-target-site resistant (NTSR) mechanisms explain resistance in C. bonariensis and C. canadensis, whereas both NTSR and target-site resistant (TSR) mechanisms contribute to resistance in C. sumatrensis. The results obtained in the field trials suggest that the resistance problem can be solved through Integrated Weed Management.
Article
s The resistance levels to glyphosate and target-site based resistance mechanisms in susceptible (S) and resistant (R) Conyza canadensis (L.) populations, which were collected from apple orchards around areas of Bohai seas and Loess Plateau in China, were investigated. Among forty C. canadensis populations, eighteen populations (45%) were still susceptible; fourteen populations (35%) evolved low resistance levels resistance to glyphosate with resistance index (RI) of 2.02 to 3.90. In contrast, eight populations (20%) evolved medium resistance levels with RI of 4.35 to 8.38. The shikimic acid concentrations in R populations were highly negative relative with the glyphosate resistance levels in C. canadensis, the Pearson correlation coefficient was − 0.82 treated by glyphosate at 1.8 mg/L. Three 5-enoylpyruvylshikimate 3′-phosphate synthase genes (EPSPS1, EPSPS2 and EPSPS3) were cloned in all S and glyphosate-resistant C. canadensis populations. No amino acid substitution was identified at site of 102 and 106 in three EPSPS genes, which were reported to confer glyphosate resistance in other weed species. The relative expression level of EPSPS mRNA in R populations (SD07, LN05, SHX06 and SD09) was 4.5 to 13.2 times higher than in S biotype. The Pearson correlation coefficient between EPSPS expression levels and RI was 0.79, which indicated the over expression of EPSPS mRNA may cause these R populations evolve higher resistance level to glyphosate.
Article
Glyphosate is the most widely used and successful herbicide discovered to date, but its utility is now threatened by the occurrence of several glyphosate-resistant weed species. Glyphosate resistance first appeared in Lolium rigidum in an apple orchard in Australia in 1996, ironically the year that the first glyphosate-resistant crop (soybean) was introduced in the USA. Thirty-eight weed species have now evolved resistance to glyphosate, distributed across 37 countries and in 34 different crops and six non-crop situations. Although glyphosate-resistant weeds have been identified in orchards, vineyards, plantations, cereals, fallow and non-crop situations, it is the glyphosate-resistant weeds in glyphosate-resistant crop systems that dominate the area infested and growing economic impact. Glyphosate-resistant weeds present the greatest threat to sustained weed control in major agronomic crops because this herbicide is used to control weeds with resistance to herbicides with other sites of action, and no new herbicide sites of action have been introduced for over 30 years. Industry has responded by developing herbicide resistance traits in major crops that allow existing herbicides to be used in a new way. However, over reliance on these traits will result in multiple-resistance in weeds. Weed control in major crops is at a precarious point, where we must maintain the utility of the herbicides we have until we can transition to new weed management technologies.