chemical weed control in saffron fields of iran s. norouzzadeh, m. abbaspoor, m. delghandi agricultural and natural resources research cen
Chemical Weed Control in Saffron Fields of Iran
S. Norouzzadeh, M. Abbaspoor, M. Delghandi
Agricultural and Natural Resources Research Center
Keywords: ethalfluralin, ioxynil, metribuzin, tribenuron-methyl,
Field experiments were conducted to assess the efficacy of herbicides
applied pre- (pre-forking) and post-emergence (after harvest) in
spring and autumn during 2000-2002 in saffron fields of Mashhad and
Gonabad located in north-eastern and eastern parts of Iran,
respectively. In spring trials, ioxynil (750 g a.i. ha-1) and
tribenoronmethyl (18.75 g a.i. ha-1) when sprayed at 6-8 leafy stage
of weeds after saffron harvest were more potent than metribuzin. In
autumn trials, weed control by ethalfloralin (1320 g a.i. ha-1) and
trifloralin (960 g a.i. ha-1) when applied pre-emergence and before
saffron flowering was promising but caused also some damages on
saffron, leading to yield loss. Application of metribuzin (560 g a.i.
ha-1) whether in spring or autumn, controlled weeds without any
saffron injury. Tribenuron-methyl and metribuzin were the best
treatments for weed control in saffron fields of Mashhad and Gonabad,
Saffron is derived from the stigmas of the saffron (Crocus sativus L).
It is the world’s most expensive spice and has been widely used in
many countries (Bolhasani et al., 2005). It is also increasingly used
for drugs purposes (Behnia et al., 1999; Bolhasani et al., 2005). Weed
control in this perennial, small and low growing crop, needs a lot of
labor work. It has been reported that glyphosate and/or 2, 4-D / 2,
4-DP are used to clean up the beds prior to the new season’s flowering
and growth of saffron in New Zealand (McGimpsey et al., 1997).
The choice of herbicide(s) depends on the kind of weeds present (McGimpsey
et al., 1997). Metribuzin inhibits photosynthesis of susceptible plant
species by inhibiting the electron transfer from primary to the
secondary quinones (QA to QB) in the electron transfer chain in
photosynthesis. It is selectively used for control of annual grasses
and numerous broad-leaved weeds (Arregui et al., 2006).
Tribenuron-methyl is a post emergence herbicide rapidly absorbed by
foliage and roots and translocated through the plant and inhibiting
biosynthesis of the essential amino acids valine and isoleucine
(Dixonand and Clay 2004). Ioxynil is inhibitor of photosynthesis at
Photosystem II and it’s recently discovered mode of action is the
inhibition of cell wall synthesis primarily. Foliar application of
ioxynil to broad-leaved weeds causes growth inhibition and swelling of
the stems (Thiel and Böger, 1986; Argese et al., 2005). Trifluralin is
a selective pre-emergence herbicide used for the control of annual
grasses and certain broadleaf weeds on some crops like Cotton and
soybean. This herbicide interfering with synthesis of microtubular
protein or metabolism of endoplasmic reticulum membranes involved in
microtubule assembly (Wang et al., 1995). Ethalfluralin which is a
member of so-called bleaching herbicides can influence the plant
growth by either inhibiting biosynthesis of chlorophyll or carotenoids
and by causing destruction of pigments already formed (Grichar et al.,
The objective of this study was the evaluation of the efficacy of
herbicides with different mode of actions, selected on the basis of
dominant weed flora, on weeds grown in saffron fields of Iran in
different times of season.
Materials and Methods
The layout was completely randomized block design with four
replications. The plot dimension was 3×6 m (18 m2). The weed density
was calculated in 1 m2-quadrate, 15 days after herbicide application.
The treatments in Mashhad were included: weed free and weed infested
controls plus metribuzin (560 g a.i. ha-1), tribenuron-methyl (18.75 g
a.i. ha-1) and ioxynil (750 g a.i. ha-1) were sprayed in spring after
harvest and in early stage of weeds growth (6-8 true-leaf stage). The
treatments in Gonabad were: weed free and weed infested controls plus
trifluralin (960 g a.i. ha-1) and ethalfluralin (1320 g a.i. ha-1)
both applied as soil-incorporated (pre-forking) and foliar application
of metribuzin (560 g a.i. ha-1) were applied before saffron flowering
in autumn. Treatments in Mashhad and Gonabad were the same in the
second year. In the third experiment in Gonabad (2002) the treatments
were consisted of: weed free and weed infested controls plus
metribuzin (560 g a.i. ha-1) applied before flowering in autumn or
after harvest in spring, tribenuron-methyl (18.75 g a.i. ha-1) and
ioxynil (750 g a.i. ha-1) both were applied in spring after harvest
and in early stage of weeds growth (6-8 true-leaf stage).
Results and Discussion
Weed flora of the experimental fields in Mashhad and Gonabad is shown
in table 1. The visual dominant weed species were Achillea millefolium
and Malcolmia africana in Mashhad and Gonabad, respectively. Cardaria
draba was the second dominant weed in both fields.
In spring application in Mashhad, ioxynil and tribenuron-methyl were
more effective than metribuzin against weeds (Fig. 1-1). Ioxynil,
however, decreased the saffron yield significantly (Fig. 1-2).
Tribenuron-methyl was the best treatment for weed control in Mashhad.
In autumn trials in Gonabad, trifluralin, ethalfluralin and metribuzin
had the same effect on weed density (Fig. 1-3). Trifluralin and
ethalfluralin, however, made significant damage on saffron leading to
yield loss remarkably (Fig. 1-4). Weeds efficiently were controlled by
metribuzin (Fig. 1-3) and this herbicide caused the much less damage
on saffron comparing to the trifluralin and ethalfluralin (Fig. 1-4).
In Gonabad in 2002 the application of herbicides, chosen from the
promising results of the previous experiments, again showed good
effects of metribuzin (when sprayed before flowering in autumn or
after harvest in spring) and tribenuron-methyl (Figs. 1-5 and 1-6).
Tribenuron-methyl in Mashhad caused no damage on saffron yield (Fig.
1-2) while in Gonabad it made significant damage comparing to the hand
weeding control (Fig. 1-6). It is mainly because younger and stronger
saffron plants were growing in Mashhad than in Gonabad. This is why
the saffron yield for hand weeding controls in Mashhad (Fig. 1-2) is
almost two-fold of that in Gonabad (Figs. 1-4 and 1-6). This
difference could also partially be refered to the better field
situation and environmental conditions as well as weed flora growing
in each place.
In summary, tribenuron-methyl (18.75 g a.i. ha-1) and metribuzin (560
g a.i. ha-1) were the best choices for weed control in saffron fields
of Mashhad and Gonabad, respectively. The results also showed
application of soil-incorporated herbicides i.e. trifluralin and
ethalfluralin, not only needs to special equipments be involved, but
also leading to significant damage on saffron yield as well,
especially when it comes to the coming years yield and profits.
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Table 1: Alphabetically ordered weed flora in experimental fields.
Coix lacryma jobi
Fig. 1. Effect of metribuzin (560 g a.i. ha-1), tribenuron-methyl
(18.75 g a.i. ha-1), ioxynil (750 g a.i. ha-1), trifluralin (960 g
a.i. ha-1) and ethalfluralin (1320 g a.i. ha-1) on weed density (1, 3,
5) and saffron yield (2, 4, 6), applied after harvest in spring or
before flowering in autumn in Mashhad and Gonabad. Trifluralin and
ethalfluralin were applied as soil-incorporated and the rest of the
herbicides were sprayed on foliage.